Neonatal airway colonization with gram-negative bacilli: association with severity of bronchopulmonary dysplasia

Incidence, Risk Factors, Short-term Outcomes, and Microbiome of Ventilator-associated Pneumonia in Very-low-birth-weight Infants: Experience at a Single Level III Neonatal Intensive Care Unit

BACKGROUND

Ventilator-associated pneumonia (VAP) is a common hospital-acquired infection in neonates on invasive mechanical ventilation, resulting in high morbidity and mortality. The objective of this study is to determine the incidence, risk factors, short-term outcomes and microbiome associated with VAP in very-low-birth-weight (VLBW) infants born at <32 weeks of gestational age (GA).

METHODS

Retrospective study of intubated VLBW infants born at <32 weeks of GA admitted to the Los Angeles General Medical Center neonatal intensive care unit from July 2015 to July 2021 who had routine tracheal aspirate cultures obtained. Neonates were retrospectively classified into 3 groups, confirmed VAP, suspected VAP and no VAP, for comparison of risk factors, outcomes and airway microbial colonization.

RESULTS

Eighty-seven infants met inclusion criteria with a mean GA of 26.1 ± 1 weeks and mean birth weight of 812 ± 281 g. The incidence of VAP was 7.8 per 1000 ventilator days, and the most common causative organisms were Gram-positive organisms (39%), predominantly coagulase-negative Staphylococcus . Duration of postnatal dexamethasone exposure predicted VAP compared to no VAP (coefficient, 0.31; 95% CI 0.03-0.59; P = 0.03) after adjusting for duration of intubation, surfactant use and antenatal steroid exposure. Infants with VAP had higher rate of grade 2/3 bronchopulmonary dysplasia ( P = 0.03) and longer hospital stay ( P = 0.04).

CONCLUSIONS

VAP occurs at a high rate in VLBW infants who are exposed to prolonged dexamethasone use. It is predominantly caused by Gram-positive organisms.

IL-17a-producing γδT cells and NKG2D signaling mediate bacterial endotoxin-induced neonatal lung injury: implications for bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in preterm birth survivors characterized by inflammation, impaired alveolarization and dysmorphic vasculature. Activated IL-17A+ lymphocytes are key drivers of inflammation in preterm infants. We have shown that in immature mice chronic airway exposure to lipopolysaccharide (LPS) induces pulmonary inflammation, increased IL-17a expression, and hypoalveolarization, a BPD-like phenotype. The source of IL-17a and contribution to lung pathology is unknown. The natural-killer group 2, member D (NKG2D) receptor mediates activation and IL-17a production in γδ T cells by binding to stress molecules. LPS induces NKG2D ligand expression, including Rae-1 and MULT1. We hypothesized that IL-17a+ γδ T cells and NKG2D signaling mediate neonatal LPS-induced lung injury. Immature C57BL/6J (wild type), Nkg2d-/- or Tcrd-/- (lacking γδ T cells) mice were inoculated with 3ug/10ul of LPS from E. coli O26:B6 or 10ul of PBS intranasally on day of life 3, 5, 7, and 10. Selected mice were treated with neutralizing antibodies against IL-17a, or NKG2D intraperitoneally. Lung immune cells were assessed by flow cytometry and gene expression was analyzed by qPCR. Alveolar growth was assessed by lung morphometry. We established that anti-IL-17a antibody treatment attenuated LPS-induced hypoalveolarization. We found that LPS induced the fraction of IL-17a+NKG2D+ γδ T cells, a major source of IL-17a in the neonatal lung. LPS also induced lung mRNA expression of NKG2D, Rae-1, MULT1, and the DNA damage regulator p53. Anti-NKG2D treatment attenuated the effect of LPS on γδ T cell IL-17a expression, immune cell infiltration and hypoalveolarization. LPS-induced hypoalveolarization was also attenuated in Nkg2d-/- and Tcrd-/- mice. In tracheal aspirates of preterm infants IL-17A and its upstream regulator IL-23 were higher in infants who later developed BPD. Also, human ligands of NKG2D, MICA and MICB were present in the aspirates and MICA correlated with median FiO2. Our novel findings demonstrate a central role for activated IL-17a+ γδ T cells and NKG2D signaling in neonatal LPS-induced lung injury. Future studies will determine the role of NKG2D ligands and effectors, other NKG2D+ cells in early-life endotoxin-induced lung injury and inflammation with a long-term goal to understand how inflammation contributes to BPD pathogenesis.

The Association between Early Gram-Negative Bacteria in Tracheal Aspirate Cultures and Severe Bronchopulmonary Dysplasia among Extremely Preterm Infants Requiring Prolonged Ventilation

OBJECTIVE

The study aimed to evaluate the association between bronchopulmonary dysplasia (BPD) development at 36 weeks' postmenstrual age (PMA) and Gram-negative bacteria in tracheal aspirate cultures among extremely preterm infants.

STUDY DESIGN

This study has a retrospective cohort. Patients were 155 infants aged less than or equal to 26 gestational weeks who were admitted to the neonatal intensive care unit of Osaka Women's and Children's Hospital from 2009 to 2018. Primary outcome was respiratory outcomes expressed as BPD development.Multivariable logistic regression analysis was used to identify neonatal and bacterial factors associated with BPD.

RESULTS

After adjusting for gestational age, birth weight, sex, chorioamnionitis, Gram-positive cocci (GPC) and Gram-negative rods (GNRs) in tracheal aspirate cultures within 28 days after birth, GNRs were significantly associated with BPD development (odds ratio [OR]: 3.88, 95% confidence interval [CI]: 1.68-8.94). In contrast, GPCs were not associated with BPD development (OR: 0.47, 95% CI: 0.05-1.61).

CONCLUSION

Gram-negative bacteria in tracheal cultures within 28 days of birth are associated with BPD development in infants aged less than or equal to 26 gestational weeks.

KEY POINTS

· BPD is a factor for morbidity in extremely preterm infants.. · Respiratory infection is an adverse outcome of BPD.. · GNRs in tracheal cultures soon after birth disturb BPD development.. · GPC was not associated with BPD development..

Moving bronchopulmonary dysplasia research from the bedside to the bench

Although advances in the respiratory management of extremely preterm infants have led to improvements in survival, this progress has not yet extended to a reduction in the incidence of bronchopulmonary dysplasia (BPD). BPD is a complex multifactorial condition that primarily occurs due to disturbances in the regulation of normal pulmonary airspace and vascular development. Preterm birth and exposure to invasive mechanical ventilation also compromises large airway development, leading to significant morbidity and mortality. Although both predisposing and protective genetic and environmental factors have been frequently described in the clinical literature, these findings have had limited impact on the development of effective therapeutic strategies. This gap is likely because the molecular pathways that underlie these observations are yet not fully understood, limiting the ability of researchers to identify novel treatments that can preserve normal lung development and/or enhance cellular repair mechanisms. In this review article, we will outline various well-established clinical observations while identifying key knowledge gaps that need to be filled with carefully designed preclinical experiments. We will address these issues by discussing controversial topics in the pathophysiology, the pathology, and the treatment of BPD, including an evaluation of existing animal models that have been used to answer important questions.

Interventions for the management of transient tachypnoea of the newborn - an overview of systematic reviews

BACKGROUND

Transient tachypnoea of the newborn (TTN) is characterised by tachypnoea and signs of respiratory distress. It is caused by delayed clearance of lung fluid at birth. TTN typically appears within the first two hours of life in term and late preterm newborns. Although it is usually a self-limited condition, admission to a neonatal unit is frequently required for monitoring, the provision of respiratory support, and drugs administration. These interventions might reduce respiratory distress during TTN and enhance the clearance of lung liquid. The goals are reducing the effort required to breathe, improving respiratory distress, and potentially shortening the duration of tachypnoea. However, these interventions might be associated with harm in the infant.

OBJECTIVES

The aim of this overview was to evaluate the benefits and harms of different interventions used in the management of TTN.

METHODS

We searched the Cochrane Database of Systematic Reviews on 14 July 2021 for ongoing and published Cochrane Reviews on the management of TTN in term (> 37 weeks' gestation) or late preterm (34 to 36 weeks' gestation) infants. We included all published Cochrane Reviews assessing the following categories of interventions administered within the first 48 hours of life: beta-agonists (e.g. salbutamol and epinephrine), corticosteroids, diuretics, fluid restriction, and non-invasive respiratory support. The reviews compared the above-mentioned interventions to placebo, no treatment, or other interventions for the management of TTN. The primary outcomes of this overview were duration of tachypnoea and the need for mechanical ventilation. Two overview authors independently checked the eligibility of the reviews retrieved by the search and extracted data from the included reviews using a predefined data extraction form. Any disagreements were resolved by discussion with a third overview author. Two overview authors independently assessed the methodological quality of the included reviews using the AMSTAR 2 (A MeaSurement Tool to Assess systematic Reviews) tool. We used the GRADE approach to assess the certainty of evidence for effects of interventions for TTN management. As all of the included reviews reported summary of findings tables, we extracted the information already available and re-graded the certainty of evidence of the two primary outcomes to ensure a homogeneous assessment. We provided a narrative summary of the methods and results of each of the included reviews and summarised this information using tables and figures.

MAIN RESULTS

We included six Cochrane Reviews, corresponding to 1134 infants enrolled in 18 trials, on the management of TTN in term and late preterm infants, assessing salbutamol (seven trials), epinephrine (one trial), budesonide (one trial), diuretics (two trials), fluid restriction (four trials), and non-invasive respiratory support (three trials). The quality of the included reviews was high, with all of them fulfilling the critical domains of the AMSTAR 2. The certainty of the evidence was very low for the primary outcomes, due to the imprecision of the estimates (few, small included studies) and unclear or high risk of bias. Salbutamol may reduce the duration of tachypnoea compared to placebo (mean difference (MD) -16.83 hours, 95% confidence interval (CI) -22.42 to -11.23, 2 studies, 120 infants, low certainty evidence). We did not identify any review that compared epinephrine or corticosteroids to placebo and reported on the duration of tachypnoea. However, one review reported on "trend of normalisation of respiratory rate", a similar outcome, and found no differences between epinephrine and placebo (effect size not reported). The evidence is very uncertain regarding the effect of diuretics compared to placebo (MD -1.28 hours, 95% CI -13.0 to 10.45, 2 studies, 100 infants, very low certainty evidence). We did not identify any review that compared fluid restriction to standard fluid rates and reported on the duration of tachypnoea. The evidence is very uncertain regarding the effect of continuous positive airway pressure (CPAP) compared to free-flow oxygen therapy (MD -21.1 hours, 95% CI -22.9 to -19.3, 1 study, 64 infants, very low certainty evidence); the effect of nasal high-frequency (oscillation) ventilation (NHFV) compared to CPAP (MD -4.53 hours, 95% CI -5.64 to -3.42, 1 study, 40 infants, very low certainty evidence); and the effect of nasal intermittent positive pressure ventilation (NIPPV) compared to CPAP on duration of tachypnoea (MD 4.30 hours, 95% CI -19.14 to 27.74, 1 study, 40 infants, very low certainty evidence). Regarding the need for mechanical ventilation, the evidence is very uncertain for the effect of salbutamol compared to placebo (risk ratio (RR) 0.60, 95% CI 0.13 to 2.86, risk difference (RD) 10 fewer, 95% CI 50 fewer to 30 more per 1000, 3 studies, 254 infants, very low certainty evidence); the effect of epinephrine compared to placebo (RR 0.67, 95% CI 0.08 to 5.88, RD 70 fewer, 95% CI 460 fewer to 320 more per 1000, 1 study, 20 infants, very low certainty evidence); and the effect of corticosteroids compared to placebo (RR 0.52, 95% CI 0.05 to 5.38, RD 40 fewer, 95% CI 170 fewer to 90 more per 1000, 1 study, 49 infants, very low certainty evidence). We did not identify a review that compared diuretics to placebo and reported on the need for mechanical ventilation. The evidence is very uncertain regarding the effect of fluid restriction compared to standard fluid administration (RR 0.73, 95% CI 0.24 to 2.23, RD 20 fewer, 95% CI 70 fewer to 40 more per 1000, 3 studies, 242 infants, very low certainty evidence); the effect of CPAP compared to free-flow oxygen (RR 0.30, 95% CI 0.01 to 6.99, RD 30 fewer, 95% CI 120 fewer to 50 more per 1000, 1 study, 64 infants, very low certainty evidence); the effect of NIPPV compared to CPAP (RR 4.00, 95% CI 0.49 to 32.72, RD 150 more, 95% CI 50 fewer to 350 more per 1000, 1 study, 40 infants, very low certainty evidence); and the effect of NHFV versus CPAP (effect not estimable, 1 study, 40 infants, very low certainty evidence). Regarding our secondary outcomes, duration of hospital stay was the only outcome reported in all of the included reviews. One trial on fluid restriction reported a lower duration of hospitalisation in the restricted-fluids group, but with very low certainty of evidence. The evidence was very uncertain for the effects on secondary outcomes for the other five reviews. Data on potential harms were scarce, as all of the trials were underpowered to detect possible increases in adverse events such as pneumothorax, arrhythmias, and electrolyte imbalances. No adverse effects were reported for salbutamol; however, this medication is known to carry a risk of tachycardia, tremor, and hypokalaemia in other settings.

AUTHORS' CONCLUSIONS

This overview summarises the evidence from six Cochrane Reviews of randomised trials regarding the effects of postnatal interventions in the management of TTN. Salbutamol may reduce the duration of tachypnoea slightly. We are uncertain as to whether salbutamol reduces the need for mechanical ventilation. We are uncertain whether epinephrine, corticosteroids, diuretics, fluid restriction, or non-invasive respiratory support reduces the duration of tachypnoea and the need for mechanical ventilation, due to the extremely limited evidence available. Data on harms were lacking.

Bronchopulmonary dysplasia as a determinant of respiratory outcomes in adult life

Respiratory disease is unfortunately common in preterm infants with the archetype being bronchopulmonary dysplasia (BPD). BPD affects approximately 50,000 preterm infants in the U.S. annually with substantial morbidity and mortality related to its pathology (alveolar, airway, and pulmonary vasculature maldevelopment). Predicting the likelihood and severity of chronic respiratory disease in these children as they age is difficult and compounded by the lack of consistent phenotyping. Barriers to understanding the actual scope of this problem include few longitudinal studies, information limited by small retrospective studies and the ever-changing landscape of therapies in the NICU that affect long-term respiratory outcomes. Thus, the true burden of adult respiratory disease caused by premature birth is currently unknown. Nevertheless, limited data suggest that a substantial percentage of children with a history of BPD have long-term respiratory symptoms and persistent airflow obstruction associated with altered lung function trajectories into adult life. Small airway disease with variable bronchodilator responsiveness, is the most common manifestation of lung dysfunction in adults with a history of BPD. The etiology of this is unclear however, developmental dysanapsis may underlie the airflow obstruction in some adults with a history of BPD. This type of flow limitation resembles that of aging adults with chronic obstructive lung disease with no history of smoking. It is also unclear whether lung function abnormalities in people with a history of BPD are static or if these individuals with BPD have a more accelerated decline in lung function as they age compared to controls. While some of the more significant mediators of lung function, such as tobacco smoke and respiratory infections have been identified, more work is necessary to identify the best means of preserving lung function for individuals born prematurely throughout their lifespan.

CCR2 Mediates Chronic LPS-Induced Pulmonary Inflammation and Hypoalveolarization in a Murine Model of Bronchopulmonary Dysplasia

The histopathology of bronchopulmonary dysplasia (BPD) includes hypoalveolarization and interstitial thickening due to abnormal myofibroblast accumulation. Chorioamnionitis and sepsis are major risk factors for BPD development. The cellular mechanisms leading to these lung structural abnormalities are poorly understood. We used an animal model with repeated lipopolysaccharide (LPS) administration into the airways of immature mice to simulate prolonged airway exposure to gram-negative bacteria, focusing on the role of C-C chemokine receptor type 2-positive (CCR2+) exudative macrophages (ExMf). Repetitive LPS exposure of immature mice induced persistent hypoalveolarization observed at 4 and 18 days after the last LPS administration. LPS upregulated the expression of lung pro-inflammatory cytokines (TNF-α, IL-17a, IL-6, IL-1β) and chemokines (CCL2, CCL7, CXCL1, and CXCL2), while the expression of genes involved in lung alveolar and mesenchymal cell development (PDGFR-α, FGF7, FGF10, and SPRY1) was decreased. LPS induced recruitment of ExMf, including CCR2+ ExMf, as well as other myeloid cells like DCs and neutrophils. Lungs of LPS-exposed CCR2−/− mice showed preserved alveolar structure and normal patterns of α-actin and PDGFRα expression at the tips of the secondary alveolar crests. Compared to wild type mice, a significantly lower number of ExMf, including TNF-α+ ExMf were recruited to the lungs of CCR2−/− mice following repetitive LPS exposure. Further, pharmacological inhibition of TLR4 with TAK-242 also blocked the effect of LPS on alveolarization, α-SMA and PDGFRα expression. TNF-α and IL-17a induced α-smooth muscle actin expression in the distal airspaces of E16 fetal mouse lung explants. In human preterm lung mesenchymal stromal cells, TNF-α reduced mRNA and protein expression of PDGFR-α and decreased mRNA expression of WNT2, FOXF2, and SPRY1. Collectively, our findings demonstrate that in immature mice repetitive LPS exposure, through TLR4 signaling increases lung inflammation and impairs lung alveolar growth in a CCR2-dependent manner.

FOSL1 is a novel mediator of endotoxin/lipopolysaccharide-induced pulmonary angiogenic signaling

Systemic sepsis is a known risk factor for bronchopulmonary dysplasia (BPD) in premature infants, a disease characterized by dysregulated angiogenesis and impaired vascular and alveolar development. We have previoulsy reported that systemic endotoxin dysregulates pulmonary angiogenesis resulting in alveolar simplification mimicking BPD in neonatal mice, but the underlying mechanisms remain unclear. We undertook an unbiased discovery approach to identify novel signaling pathways programming sepsis-induced deviant lung angiogenesis. Pulmonary endothelial cells (EC) were isolated for RNA-Seq from newborn C57BL/6 mice treated with intraperitoneal lipopolysaccharide (LPS) to mimic systemic sepsis. LPS significantly differentially-regulated 269 genes after 6 h, and 1,934 genes after 24 h. Using bioinformatics, we linked 6 h genes previously unknown to be modulated by LPS to 24 h genes known to regulate angiogenesis/vasculogenesis to identify pathways programming deviant angiogenesis. An immortalized primary human lung EC (HPMEC-im) line was generated by SV40 transduction to facilitate mechanistic studies. RT-PCR and transcription factor binding analysis identified FOSL1 (FOS like 1) as a transcriptional regulator of LPS-induced downstream angiogenic or vasculogenic genes. Over-expression and silencing studies of FOSL1 in immortalized and primary HPMEC demonstrated that baseline and LPS-induced expression of ADAM8, CXCR2, HPX, LRG1, PROK2, and RNF213 was regulated by FOSL1. FOSL1 silencing impaired LPS-induced in vitro HPMEC angiogenesis. In conclusion, we identified FOSL1 as a novel regulator of sepsis-induced deviant angiogenic signaling in mouse lung EC and human fetal HPMEC.

The association between the microbes in the tracheobronchial aspirate fluid and bronchopulmonary dysplasia in preterm infants

OBJECTIVE

The study aimed to evaluate the association between microbes in the lower respiratory tract (LRT) and the srisk for severe bronchopulmonary dysplasia (sBPD) in premature infants.

METHODS

We conducted a retrospective, single-center study of preterm infants who were admitted to the neonatal intensive care unit (NICU) of Southern Medical University Affiliated Maternal & Child Health Hospital of Foshan, China, between January 2015 and December 2017. The microbes in the LRT were screened by using tracheobronchial aspirate fluid (TAF) culture.

RESULTS

One hundred and fifty-five infants were included in the analysis. Among 155 infants, 41 were diagnosed with sBPD, and 114 were diagnosed without sBPD. There were significant differences between infants with and without sBPD in regard to birth weight (BW), gestational age (GA), the duration of endotracheal ventilation and supplemental oxygen. The incidence of retinopathy (ROP) and sepsis was higher in the sBPD infants than in the infants without sBPD. There was a difference in the detection rate of Gram-negative bacteria (GNB) between the two groups. Stenotrophomonas maltophilia and Klebsiella pneumoniae were mainly detected in TAF.

CONCLUSIONS

The LRT microbes were different between infants with and without sBPD, and GNB is more frequently detected in sBPD infants.

Neonate Bloodstream Infections in Organization for Economic Cooperation and Development Countries: An Update on Epidemiology and Prevention

The term neonatal sepsis is used to describe a generalized bloodstream infection of bacterial, viral, or fungal origin which is associated with hemodynamic changes and other clinical symptoms and signs, however, there is no unified definition. There are no basic criteria regarding differentiation of early-onset sepsis (EOS) versus late-onset sepsis (LOS). Stratification used in studies on neonatal sepsis also rarely includes the general condition of the newborn according to unambiguous assessment at birth, which hampers the establishment of a clear, uniform epidemiological description of neonatal sepsis. We aim to review the published data about the epidemiology and microbiology of sepsis in Organization for Economic Cooperation and Development (OECD) countries. Data was also collected on sepsis prevention programs that can be implemented in neonatal units. The outcomes of interest were incidence or incidence density of EOS and LOS, microbiology of EOS and LOS, and data on the methodology of the research, in particular the criteria for inclusion and exclusion of newborns from the study. Pubmed, EMBASE, LILACS Embase, Scopus, and Google Scholar were used. For the preselection step, inclusion criteria included: "bloodstream infection" or "neonatal sepsis" (MesH), "very low birth weight", and "country" full-text studies, human, and English language. Exclusion criteria included: studies published in languages other than English and studies available only as an abstracts. For proper selection, inclusion criteria included: information about epidemiology or microbiology bloodstream infection (BSI), study population and case definitions, exclusion criteria, narrative reviews, commentaries, case studies, pilot studies, study protocols, pediatric studies, and only clinical data (without microbiology or epidemiology) or studies with only one etiological factor analysis. The data review indicated the lack of an unequivocal, unified definition and no unambiguous basic criteria with regard to differentiation of EOS versus LOS. Among infants <1500 g, studies reported an EOS rate from 7% to 2%. For studies using other definitions (mostly all inborn babies), the rate of EOS ranged from 1% to 3%. The LOS incidences were much more varied among countries; the highest rates were in the multicenter studies focused on very low birth weight (VLBW) infants. The main pathogens in EOS are GBS and Gram-negative bacteria in LOS. Our review data shows that LOS microbiology is very diverse and that Gram-positive cocci, especially staphylococci, predominate versus Gram-negative rods. Unfortunately, the lack of uniform, international prevention programs results in high newborn morbidity and insufficient postnatal prevention of late-onset infections.

Respiratory morbidity in children with cerebral palsy: an overview

Respiratory problems have a significant impact on morbidity and mortality in patients with cerebral palsy (CP). In particular, recurrent aspiration, impaired airway clearance, spinal and thoracic deformity, impaired lung function, poor nutritional status, and recurrent respiratory infections negatively affect respiratory status. Bronchopulmonary dysplasia may contribute to pulmonary problems, but asthma is not more common in CP than in the general population. We discuss treatment options for each of these factors. Multiple coexisting and interacting factors that influence the respiratory status of patients with CP should be recognized and effectively addressed to reduce respiratory morbidity and mortality. WHAT THIS PAPER ADDS: Respiratory problems are a significant cause of morbidity in patients with cerebral palsy (CP). Respiratory status in patients with CP is influenced by recurrent aspiration and impaired airway clearance. Spinal and thoracic deformity, impaired lung function, poor nutrition, and respiratory infections also negatively affect respiratory status. These factors should all be addressed to reduce respiratory problems in patients with CP.

Control of Acinetobacter baumannii outbreak in the neonatal intensive care unit in Latvia: whole-genome sequencing powered investigation and closure of the ward

Background

Acinetobacter baumannii is an emerging pathogen capable of causing hospital-acquired infections (HAIs). It has the ability to survive on environmental surfaces for months, making transmission difficult to control. Our report describes the investigation and restriction of an outbreak of A.baumannii in the Neonatal Intensive Care Unit (NICU) using whole-genome sequencing (WGS) and multi-modal infection control measures.

Methods

A prospective surveillance of HAIs was initiated in the NICU at the Pauls Stradins Clinical University Hospital (PSCUH) in Latvia on 1/9/2012 and identified an outbreak of A.baumannii. Case definitions for A.baumannii bloodstream infection (BSI) and colonization were implemented; surveillance cultures were obtained from all admitted patients to monitor the rate of colonization; an infection prevention and control team was formed and infection control interventions implemented. Environmental sampling of the NICU and Labour ward was performed. We employed WGS to differentiate phenotypically identical multidrug-resistant A.baumannii (MDRAB) strains from simultaneous intrahospital outbreaks in the adult Intensive Care Unit and NICU.

Results

Between 1/9/2012 and 31/12/2017 the surveillance included 2157 neonates. A total of 17 neonates had A.baumannii BSI, with the highest rate of 30.0 cases per 1000 bed-days in November 2012. Rectal screening samples were positive for A.baumannii-complex in 182 neonates reaching 119.6 per 1000 bed-days in July 2015. All 298 environmental cultures were negative. Two phenotypically identical MDRAB isolates from the simultaneous intrahospital outbreaks were differentiated using WGS, ruling out an inter-ward transmission. Adherence to stringent infection control measures decreased BSI cases but colonization remained persistent. With several relapses, the outbreak was ongoing for four years. No new A.baumannii BSI cases were registered after total environmental decontamination in the NICU in July 2015. Colonization reappeared and persisted until in November 2016 when the ward was temporarily closed, relocated and renovated. No A.baumannii cases were registered after the renovation.

Conclusion

The HAI surveillance system successfully detected and facilitated the control of the A.baumannii outbreak. Whole-genome sequencing was found to be a useful method for differentiation of phenotypically identical A.baumannii strains from the intrahospital outbreak. Only multi-modal infection control program, including closure, temporary relocation, and renovation of the ward, restricted the outbreak.

Interpretation and Relevance of Advanced Technique Results

Advanced techniques in the field of diagnostic microbiology have made amazing progress over the past 25 years due largely to a technological revolution in the molecular aspects of microbiology [1, 2]. In particular, rapid molecular methods for nucleic acid amplification and characterization combined with automation in the clinical microbiology laboratory as well as user-friendly software and robust laboratory informatics systems have significantly broadened the diagnostic capabilities of modern clinical microbiology laboratories. Molecular methods such as nucleic acid amplification tests (NAATs) rapidly are being developed and introduced in the clinical laboratory setting [3, 4]. Indeed, every section of the clinical microbiology laboratory, including bacteriology, mycology, mycobacteriology, parasitology, and virology, has benefited from these advanced techniques. Because of the rapid development and adaptation of these molecular techniques, the interpretation and relevance of the results produced by such molecular methods continues to lag behind. The purpose of this chapter is to review, update, and discuss the interpretation and relevance of results produced by these advanced molecular techniques.

Pilot study of dornase alfa (Pulmozyme) therapy for acquired ventilator-associated infection in preterm infants

OBJECTIVE

Evaluate the feasibility, safety, and efficacy of adjunctive treatment with dornase alfa in preterm patients with ventilator-associated pulmonary infection (VAPI) compared to standard care.

WORKING HYPOTHESIS

We hypothesize that therapy with dornase alfa will be safe and well tolerated in the preterm population with no worsening of symptoms, oxygen requirement, or need for respiratory support.

STUDY DESIGN

Prospective, randomized, blinded, pilot study comparing adjunctive treatment with dornase alfa to sham therapy. In addition to standard care, infants were randomized to receive dornase alfa 2.5 mg nebulized via endotracheal tube (ETT) every 12 hr for 7 days or sham therapy. ETT secretion gram stain and culture and chest X-ray (CXR) findings were evaluated. Respiratory support data were downloaded from the ventilator.

RESULTS

Fourteen infants developed VAPI between 2012 and 2014; 11 enrolled in the study. Six received dornase alfa and five received sham therapy. Average gestational age at birth was 25 weeks and age at study entry was 31 days. There were no differences in demographics, ETT white blood cell count (WBC), CXR, or mean airway pressure (MAP) between the two groups. There was a trend towards decreased oxygen requirement (FiO2) in the treatment group that did not reach statistical significance. No side effects were observed in the treatment group.

CONCLUSION

Treatment with dornase alfa is safe and treated infants had some improvement in FiO₂ requirement but no improvement in MAP. A larger randomized trial is needed to evaluate the efficacy of this therapy. Pediatr Pulmonol. 2017; 52:787-791. © 2017 Wiley Periodicals, Inc.

Association of TLR polymorphisms with bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) remains a leading cause of morbidity and mortality during infancy. Evidence suggests that the Toll-like receptor (TLR) signaling pathway plays an integral role in lung inflammation and injury. This study aimed to detect single nucleotide polymorphisms (SNPs) in TLR pathway genes [TLR5 and Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP)] among preterm neonates and to determine their association with the development and severity of bronchopulmonary dysplasia.

Physiology of non-invasive respiratory support

Non-invasive ventilation (NIV) is used in neonates to treat extrathoracic and intrathoracic airway obstruction, parenchymal lung disease and disorders of control of breathing. Avoidance of airway intubation is associated with a reduction in the incidence of chronic lung disease among preterm infants with respiratory distress syndrome. Use of nasal continuous positive airway pressure (nCPAP) may help establish and maintain functional residual capacity (FRC), decrease respiratory work, and improve gas exchange. Other modes of non-invasive ventilation, which include heated humidified high-flow nasal cannula therapy (HHHFNC), nasal intermittent mandatory ventilation (NIMV), non-invasive pressure support ventilation (NI-PSV), and bi-level CPAP (SiPAP™), have also been shown to provide additional benefit in improving breathing patterns, reducing work of breathing, and increasing gas exchange when compared with nCPAP. Newer modes, such as neurally adjusted ventilatory assist (NAVA), hold the promise of improving patient-ventilator synchrony and so might ultimately improve outcomes for preterm infants with respiratory distress.

Lipopolysaccharide (LPS)-mediated angiopoietin-2-dependent autocrine angiogenesis is regulated by NADPH oxidase 2 (Nox2) in human pulmonary microvascular endothelial cells

Sepsis-mediated endothelial Angiopoeitin-2 (Ang2) signaling may contribute to microvascular remodeling in the developing lung. The mechanisms by which bacterial cell wall components such as LPS mediate Ang2 signaling in human pulmonary microvascular endothelial cells (HPMECs) remain understudied. In HPMEC, LPS-induced Ang2, Tie2, and VEGF-A protein expression was preceded by increased superoxide formation. NADPH oxidase 2 (Nox2) inhibition, but not Nox4 or Nox1 inhibition, attenuated LPS-induced superoxide formation and Ang2, Tie2, and VEGF-A expression. Nox2 silencing, but not Nox4 or Nox1 silencing, inhibited LPS-mediated inhibitor of κ-B kinase β (IKKβ) and p38 phosphorylation and nuclear translocation of NF-κB and AP-1. In HPMECs, LPS increased the number of angiogenic tube and network formations in Matrigel by >3-fold. Conditioned media from LPS-treated cells also induced angiogenic tube and network formation in the presence of Toll-like receptor 4 blockade but not in the presence of Ang2 and VEGF blockade. Nox2 inhibition or conditioned media from Nox2-silenced cells attenuated LPS-induced tube and network formation. Ang2 and VEGF-A treatment rescued angiogenesis in Nox2-silenced cells. We propose that Nox2 regulates LPS-mediated Ang2-dependent autocrine angiogenesis in HPMECs through the IKKβ/NF-κB and MAPK/AP-1 pathways.

The airway microbiome of intubated premature infants: characteristics and changes that predict the development of bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is associated with perinatal inflammatory triggers. Methods targeting bacterial rRNA may improve detection of microbial colonization in premature infants. We hypothesize that respiratory microbiota differs between preterm infants who develop BPD and those unaffected and correlates with inflammatory mediator concentrations.

METHODS

Twenty-five infants, born at ≤32 wk of gestation and intubated in the first 24 h, were enrolled. Tracheal aspirates were obtained at intubation and on days 3, 7, and 28. Bacterial DNA was extracted, and 16S rRNA genes were amplified and sequenced. Concentrations of interleukins (IL-1β, IL-6, IL-8, IL-10, and IL-12), tumor necrosis factor-α, interferon-γ, lipopolysaccharide (LPS), and lipoteichoic acid (LTA) were measured. Chorioamnionitis was diagnosed by histology. BPD was defined as an oxygen requirement at 36 wk postmenstrual age.

RESULTS

Acinetobacter was the predominant genus in the airways of all infants at birth. Ten infants developed BPD and showed reduced bacterial diversity at birth. No differences were detected in bacterial diversity, cytokines, LPS, and LTA from infants with and without exposure to chorioamnionitis.

CONCLUSION

The airways of premature infants are not sterile at birth. Reduced diversity of the microbiome may be an important factor in the development of BPD and is not associated with differences in inflammatory mediators.

Interpretation and Relevance of Advanced Technique Results

Advanced techniques in the field of diagnostic microbiology have made amazing progress over the past two decades due largely to a technological revolution in the molecular aspects of microbiology [1, 2]. In particular, rapid molecular methods for nucleic acid amplification and characterization combined with automation and user-friendly software have significantly broadened the diagnostic capabilities of modern clinical microbiology laboratories. Molecular methods such as nucleic acid amplification tests (NAATs) rapidly are being developed and introduced in the clinical laboratory setting. Indeed, every section of the clinical microbiology laboratory, including bacteriology, mycology, mycobacteriology, parasitology, and virology, have benefited from these advanced techniques. Because of the rapid development and adaptation of these molecular techniques, the interpretation and relevance of the results produced by such molecular methods has lagged somewhat behind. The purpose of this chapter is to review and discuss the interpretation and relevance of results produced by these advanced molecular techniques. Moreover, this chapter will address the “myths” of NAATs, as these myths can markedly influence the interpretation and relevance of these results.

Endotracheal tube: friend or foe? Bacteria, the endotracheal tube, and the impact of colonization and infection

The microbiology of the endotracheal tube culture plays a role in diagnosing a variety of diseases in the newborn intensive care unit, including subglottic stenosis, bronchopulmonary dysplasia, and ventilator-associated pneumonia. Bacterial production of a biofilm that coats the endotracheal tube acts as a reservoir for infection, prevents eradication, and may play a role in the development of subglottic stenosis. The diagnosis of ventilator-associated pneumonia is limited by the CDC definition as well as currently available diagnostic methods. Biomarkers could aid in differentiating colonization from infection, but are not available to most clinicians. The etiology of ventilator-associated pneumonia is often polymicrobial. Failure to differentiate colonization from infection results in unnecessary prescription of antibiotics, which could contribute to antimicrobial resistance. Measures to prevent ventilator-associated pneumonia have been described, primarily in the adult population.

A TLR5 (g.1174C > T) variant that encodes a stop codon (R392X) is associated with bronchopulmonary dysplasia

Current evidence supports a major role for inherited factors in determining bronchopulmonary dysplasia (BPD) susceptibility. The Toll-like receptor (TLR) family of proteins maintain pulmonary homeostasis in the developing lung by aiding pathogen recognition and clearance, regulating inflammation, and facilitating reparative tissue growth. We hypothesized that sequence variation in the TLR pathway genes would alter the susceptibility/severity of BPD in preterm infants. Very low birth-weight infants were recruited prospectively in a multi-center study involving collection of blood samples and clinical information. Nine TLR pathway single-nucleotide polymorphisms were genotyped using a multiplexed single-base extension assay. BPD outcomes were compared among infants with and without the variant allele using Chi-square or Fisher's exact tests. In our cohort (n = 289), 66 (23.6%) infants developed BPD, out of which 32 (11.2%) developed severe BPD. The TLR5 (g.1174C > T) variant was associated with BPD (P = 0.03) and severe BPD (P = 0.004). The TIRAP (g.2054C > T) variant was associated with BPD (P = 0.04). Infants heterozygous for the X-linked IRAK1 (g.6435T > C) variant had a lower incidence of BPD compared to infants homozygous for either the reference or variant allele (P = 0.03). In regression models that controlled for potential epidemiological confounders, the TIRAP variant was associated with BPD, and the TLR5 variant was associated with severe BPD. Our data support the hypothesis that aberrant pathogen recognition in premature infants arising from TLR pathway genetic variation can contribute to BPD pathogenesis.

Antenatal exposure to Ureaplasma species exacerbates bronchopulmonary dysplasia synergistically with subsequent prolonged mechanical ventilation in preterm infants

INTRODUCTION

The presence of microorganisms in gastric fluid in neonates at birth is postulated to reflect antenatal infection and also to be associated with the development of bronchopulmonary dysplasia (BPD).

RESULTS

A logistic regression analysis, after controlling for other risk factors, indicated that Ureaplasma-positive infants were not at increased risk for moderate/severe BPD (adjusted odds ratio (OR): 2.58, 95% confidence interval (CI): 0.57-6.89, P = 0.12). However, the association between the presence of Ureaplasma species and the risk for moderate/severe BPD increased significantly in infants on mechanical ventilation (MV) ≥2 wk (adjusted OR: 4.17, 95% CI: 1.62-44.1, P = 0.009). An analysis using a lung injury marker indicated that Ureaplasma-positive infants with MV ≥2 wk, but not other infants, showed higher serum KL-6 levels in samples taken from cord blood, and that KL-6 levels increased time-dependently up to 4 wk of age.

DISCUSSION

Antenatal exposure to Ureaplasma species induces lung injury prior to birth and synergistically contributes to the development of BPD in infants requiring prolonged MV (≥2 wk).

METHODS

We recovered gastric fluid specimens from 122 infants with gestational age (GA) <29 wk or birth weight <1,000 g to investigate whether these microorganisms influence respiratory outcome of BPD. A PCR analysis was used to detect urease and 16S ribosomal RNA (rRNA) genes to classify neonates into Ureaplasma-positive or Ureaplasma-negative infants.

Interpreting positive cultures of endotracheal aspirates: factors associated with treatment decisions in ventilated neonates

AIMS

Diagnosis of ventilator-associated pneumonia in newborns is challenging because of ease of colonisation, non-specific chest radiograph changes and lack of a consensus definition. The aims of this study were to review treatment decisions in neonates with culture-positive endotracheal aspirate and to assess impact on respiratory outcomes using blinded review of radiological studies.

METHODS

Charts from all very low birthweight neonates ventilated for >48 h and with positive culture were assessed. Chest radiographs were reviewed by a radiologist masked to the grouping of the episode (treated/not treated). Clinical, investigational and radiological features used in practice were assessed on impact on treatment decisions. Association between treatment and outcomes was assessed.

RESULTS

Seventy-four episodes of culture-positive endotracheal aspirate were analysed in 38 babies. Fifty-eight episodes were treated with antibiotics. Gestational age at birth and birthweight in both groups (treated vs. non-treated) were statistically comparable (25.5 ± 3.1 vs. 27.2 ± 2.3 weeks and 809 ± 302 vs. 870 ± 262 g). Comparative chest radiographs were available in 51 of 58 treated episodes; deterioration was noted in 42 (82.3%). Ventilatory parameters were significantly higher in the treatment group and showed a significant improvement after antibiotics. Twenty-three babies developed chronic lung disease. Odds ratio (of having chronic lung disease when treatment is initiated) was 4.5 (95% confidence interval = 0.97-20.8, P= 0.06).

CONCLUSIONS

Treated culture-positive aspirate episodes were accompanied by higher ventilatory requirements, increased symptoms and elevated septic markers. Need for treatment was associated with greater likelihood of developing chronic lung disease.

Biomarkers of neutrophil-mediated glutathione and protein oxidation in tracheal aspirates from preterm infants: association with bacterial infection

Bronchopulmonary dysplasia is associated with neutrophil infiltration into the lungs and oxidative injury. However, the pathological importance of neutrophil oxidants is still not clear. Nosocomial pneumonia is also implicated, but the evidence is limited, in part because of the difficulty of distinguishing genuine infection from bacterial colonization. Good biomarkers of neutrophil oxidant activity and lung infection are needed. We tested whether glutathione sulfonamide, a product of glutathione oxidation by myeloperoxidase-derived hypochlorous acid (HOCl) and a potential new neutrophil oxidant biomarker, is detectable in endotracheal aspirates from ventilated preterm infants. As infectious organisms stimulate neutrophils to generate HOCl, we determined whether levels of HOCl-specific biomarkers were increased in samples that were bacterial culture positive. Glutathione sulfonamide was detected in 66 of 87 endotracheal aspirate samples. Levels correlated with myeloperoxidase activity and another HOCl-specific marker, chlorotyrosine. Median levels of glutathione sulfonamide (4-fold) and other biomarkers (2-fold) were significantly higher in culture positive aspirates. Staphylococcus epidermidis, a frequent colonizer, was associated with glutathione sulfonamide levels no different from those in negative samples. Glutathione sulfonamide showed good sensitivity and specificity for detecting bacterial growth and has promise for detecting lung infection.

Attenuation of lipopolysaccharide-induced oxidative stress and apoptosis in fetal pulmonary artery endothelial cells by hypoxia

Pulmonary vascular endothelial injury resulting from lipopolysaccharide (LPS) and oxygen toxicity contributes to vascular simplification seen in the lungs of premature infants with bronchopulmonary dysplasia. Whether the severity of endotoxin-induced endothelial injury is modulated by ambient oxygen tension (hypoxic intrauterine environment vs. hyperoxic postnatal environment) remains unknown. We posited that ovine fetal pulmonary artery endothelial cells (FPAEC) will be more resistant to LPS toxicity under hypoxic conditions (20-25 Torr) mimicking the fetal milieu. LPS (10 microg/ml) inhibited FPAEC proliferation and induced apoptosis under normoxic conditions (21% O(2)) in vitro. LPS-induced FPAEC apoptosis was attenuated in hypoxia (5% O(2)) and exacerbated by hyperoxia (55% O(2)). LPS increased intracellular superoxide formation, as measured by 2-hydroxyethidium (2-HE) formation, in FPAEC in normoxia and hypoxia. 2-HE formation in LPS-treated FPAEC increased in parallel with the severity of LPS-induced apoptosis in FPAEC, increasing from hypoxia to normoxia to hyperoxia. Differences in LPS-induced apoptosis between hypoxia and normoxia were abolished when LPS-treated FPAEC incubated in hypoxia were pretreated with menadione to increase superoxide production. Apocynin decreased 2-HE formation, and attenuated LPS-induced FPAEC apoptosis under normoxic conditions. We conclude that ambient oxygen concentration modulates the severity of LPS-mediated injury in FPAEC by regulating superoxide levels produced in response to LPS.

The role of inflammation and infection in the development of chronic lung disease of prematurity

CLD is a significant cause of infant morbidity and mortality. The lung injury is multifactorial in origin with supplemental oxygen and ventilatory damage being only part of the picture. Antenatal and postnatal infection and inflammation are also important in the development of CLD, although their precise role has still to be fully ascertained. In the future, therapeutic strategies need to be considered to decrease the incidence and severity of CLD. In particular a definitive trial investigating the role of antibiotics against Ureaplasma urealyticum in preventing CLD needs to be performed. Increased use of newer microbiological methods will also improve our understanding of the role of infection in CLD and further guide research and clinical management.

High levels of CXCL8 in tracheal aspirate samples taken at birth are associated with adverse respiratory outcome only in preterm infants younger than 28 weeks gestation

We investigated the relation between perinatal endotracheal colonization, the associated cytokine response and respiratory outcome in ventilated preterm neonates. Between September 1999 and March 2002, a cohort of 141 neonates with a gestational age <31 weeks requiring ventilation directly after birth, were followed prospectively. All were admitted to the Neonatal Intensive Care Unit, University Hospital of Antwerp, Belgium. A tracheal aspirate (TA) sample was collected soon after birth and was processed for microbiological examination, leukocyte count, and cytokine analysis (interleukins [IL] IL-1beta, IL-6, CXCL8 (formerly called IL-8), IL-10, IL-12p70 and tumor necrosis factor alpha [TNF-alpha]). Together with the prospectively registered patient's comorbidities and severity of disease, these inflammatory parameters were analyzed in a multivariate Cox proportional hazards model with time of extubation and duration of oxygen therapy as main outcome measures. Of the 141 patients included, 31 (22%) died before discharge from the unit and 37 (26%) had a positive TA culture. Independent predictors of duration of mechanical ventilation were: gestational age <28 weeks, degree of respiratory distress syndrome (RDS) at birth, significant patent ductus arteriosus (PDA), the SNAP-score, and high levels of CXCL8 (>4,153 pg/ml) in TA only in neonates with a gestational age <28 weeks. Variables associated with extended duration of oxygen therapy were gestational age <28 weeks, birth weight <1,000 g, degree of RDS at birth, and duration of mechanical ventilation.

Altered postnatal lung development in C3H/HeJ mice

C3H/HeJ mice develop an increase in terminal air space area detectable by postnatal d 14 that persists into adulthood compared with strain-matched controls (C3H/SnJ, C3H/OuJ). Morphometric quantification revealed a 50% increase in terminal air space area by postnatal d 14 and a 2.3-fold increase by 2 mo of age in C3H/HeJ mice. Bacteriologic cultures obtained from the left lung on postnatal d 7 revealed > 100 colony-forming units (CFU)/left lung of predominantly Gram-negative bacteria (GNB) (Escherichia coli and Proteus mirabilis) in 13 of the 14 C3H/HeJ mice compared with 0 of 12 controls demonstrating colonization of the developing lung in C3H/HeJ mice. An approximately threefold increase in macrophages from bronchoalveolar lavage, threefold increases in matrix metalloproteinase 12 (MMP-12) mRNA and protein levels and elevated levels of proinflammatory cytokines monocyte chemoattractant protein (MCP-1) and keratinocyte-derived cytokine (KC) were also found. P. mirabilis obtained from lung cultures in C3H/HeJ mice induced nuclear factor-kappaB (NF-kappaB) activation in human embryonic kidney 293 (HEK 293) cells transfected with TLR5. In C3H/HeJ mice lacking TLR4 signaling, bacterial colonization is associated with chronic inflammation and permanent changes in lung morphology.

Inflammation and bronchopulmonary dysplasia: a continuing story

Increasing evidence indicates that bronchopulmonary dysplasia (BPD) results, at least in part, from an imbalance between pro-inflammatory and anti-inflammatory mechanisms, with a persistent imbalance that favours pro-inflammatory mechanisms. The inflammatory response is characterised by an accumulation of neutrophils and macrophages in the airways and pulmonary tissue of preterm infants and, moreover, by an arsenal of pro-inflammatory mediators which affect the alveolar capillary unit and tissue integrity. As well as pro-inflammatory cytokines and toxic oxygen radicals, various lipid mediators as well as potent proteases may be responsible for acute lung injury. During the last decade it has become evident that multiple pre- and postnatal events contribute to the development of BPD in preterm infants. Chorioamnionitis and cytokine exposure in utero, plus sequential lung injury caused by postnatal resuscitation, oxygen toxicity, volu-, barotrauma and infection all lead to a pulmonary inflammatory response which is most probably associated with aberrant wound healing and an inhibition of alveolarisation as well as vascular development in the immature lungs of very preterm infants, causing the 'new BPD'.

Nebulized pentoxifylline for prevention of bronchopulmonary dysplasia in very low birth weight infants: a pilot clinical study

OBJECTIVE

To evaluate the effectiveness of nebulized pentoxifylline (PTXF) compared to intravenous dexamethasone (DX) or placebo (nebulized distilled water) for the prevention of bronchopulmonary dysplasia (BPD).

METHODS

One hundred and fifty very low birth weight infants were randomly assigned to three groups. Entry criteria were the need for oxygen administration on the fourth day of life, irrespective of whether ventilatory support was required. PTXF was administered with a nebulizer every 6 hours on three consecutive days (a single course) in a dose of 20 mg/kg when infants were breathing spontaneously or 10 mg/kg when they needed ventilatory support. DX was given every 12 hours on three consecutive days in a dose of 0.25 mg/kg. Nebulized distilled water was administered with the schedule of inhalation as in the PTXF group. When the need for ventilatory support or oxygen dependency persisted, the course of both drugs and placebo administration was repeated every seven days until the diagnosis of BPD was established.

RESULTS

Both PTXF and DX reduced the incidence of disease when compared with placebo. The respective data obtained for the PTXF-group versus the placebo group were as follows: difference in risk, 27%; OR: 0.32; CI: 0.11-0.94; p = 0.039; whereas the results for the DX-group versus the placebo group were: difference in risk, - 23%; OR: 0.39; CI: 0.14-1.14; p = 0.07.

CONCLUSION

Our data show that nebulized PTXF reduces the risk of BPD and may be a potential alternative to steroids in the prevention of this disease.

Pulmonary inflammation and bronchopulmonary dysplasia

Various pre- and postnatal risk factors, which act additively or synergistically induce an injurious inflammatory response in the airways and the pulmonary interstitium of preterm infants with bronchopulmonary dysplasia. This inflammatory response is characterized by an accumulation of neutrophils and macrophages as well as an arsenal of proinflammatory mediators that affect the endothelium and alveolar-capillary integrity. Besides proinflammatory cytokines and toxic oxygen radicals, lipid mediators as well as potent proteases may be responsible for acute lung injury. There is increasing evidence that an imbalance between pro- and anti-inflammatory factors, which should protect the alveoli and lung tissue, are key features in the pathogenesis of bronchopulmonary dysplasia. In addition, a subnormal generation of growth factors may affect alveolarization and vascular development in preterm infants with bronchopulmonary dysplasia. In this condensed review article, the current concepts on the possible role of inflammation in the evolution of bronchopulmonary dysplasia will be summarized.

Disordered pulmonary myofibroblast distribution and elastin expression in preterm infants with Ureaplasma urealyticum pneumonitis

Respiratory colonization of preterm infants with Ureaplasma urealyticum is a significant risk factor for bronchopulmonary dysplasia, a chronic lung disease characterized by arrest of alveolar development, variable interstitial fibrosis, and disordered elastic fibers in the distal airspaces. As indicated in previous studies, moderate to severe fibrosis is a hallmark of pathology in the Ureaplasma-infected preterm lung. To further characterize the preterm lung's response to Ureaplasma, lung specimens from 4 gestational controls (GC), 12 other pneumonia and 5 Ureaplasma-infected infants were analyzed by immunohistochemistry for alpha-smooth muscle actin (alphaSMA) and transforming growth factor beta1 (TGFbeta1), Hart's elastin staining, and in situ hybridization for tropoelastin (TE) expression. Cells positive for alphaSMA were observed in thickened, extensive bundles surrounding terminal airspaces in Ureaplasma and other pneumonia cases compared to individual myofibroblasts in GC. The myofibroblast pattern correlated with the severity of fibrosis, but not duration of ventilation. Transforming growth factor beta1 immunostaining was primarily localized to alveolar macrophages and was increased in Ureaplasma more than in other pneumonia cases. Elastic fibers and TE-expressing cells were spatially limited to emerging septal tips in GC. In pneumonia cases, increased deposition of elastic fibers was observed surrounding terminal airspaces, but TE expression was similar to GC. In Ureaplasma specimens, accumulation of elastic fibers correlated with duration of ventilation, and TE expression was extensive throughout the walls of terminal airspaces. These findings suggest that Ureaplasma is associated with alveolar macrophage TGFbeta1 immunostaining and myofibroblast proliferation contributing to abnormal septation, interstitial fibrosis, and a prolonged and strong elastogenic response in the preterm lung.

Critical appraisal of the role of Ureaplasma in the development of bronchopulmonary dysplasia with metaanalytic techniques

BACKGROUND

Controversy exists over whether or not Ureaplasma colonization or infection of the respiratory tract contributes to the development of bronchopulmonary dysplasia (BPD). Because BPD is a major cause of morbidity and mortality in preterm infants and a potential therapeutic intervention with antimicrobials is possible, we sought to evaluate and critique the current medical literature and to document the reported association between Ureaplasma and BPD.

METHODS

We analyzed all peer-reviewed articles and previous reviews including cross-references that reported Ureaplasma respiratory tract colonization or infection and development of BPD in neonates published from January 1966 to December 2004. Inclusion criteria included a cohort limited to all neonatal intensive care unit admissions or all colonized infants, articles that did not define a numerator and a denominator for BPD and Ureaplasma or that included patients from other reports were excluded from the analysis. We evaluated BPD at 28 postnatal days (BPD28) or 36 weeks post-menstrual age (BPD36).

RESULTS

Twenty-three studies with an aggregate of 2216 infants reported BPD28, and 8 studies with 751 infants reported BPD36. Although there was significant association between Ureaplasma colonization and both BPD28 and BPD36, there was substantial heterogeneity (Q test statistic, P < 0.01). We therefore focused on describing the study characteristics associated with an increased relative proportion of BPD. The greatest contribution to effect was from the studies enrolling fewer than 100 infants.

CONCLUSION

Ureaplasma colonization is associated with higher reported rates of BPD, but the greatest reported effect is seen in small studies; reporting bias may be partially responsible for this effect.

Septicemia in the first week of life in a Norwegian national cohort of extremely premature infants

OBJECTIVES

To investigate the incidence, causes, predictors, and outcomes of septicemia in the first week of life in a national cohort of extremely premature infants.

METHODS

A prospective study of survival of all infants with gestational age of <28 weeks or birth weight of <1000 g who were born in Norway in 1999-2000 was performed. Data on the maternal prenatal history, delivery, and neonatal course, including detailed information on episodes of microbiologically verified septicemia, were collected on predefined forms. Septicemia was reported in 2 groups, ie, episodes diagnosed on the day of delivery (ie, very early-onset septicemia [VEOS]) and episodes diagnosed from day 2 to day 7 of life (ie, early-onset septicemia [EOS]). Logistic regression models were used for the selection of variables for predictor analysis in each group.

RESULTS

Of 462 included infants, VEOS occurred for 15 (32.5 per 1000 population) and EOS for 15 (35.5 per 1000 population). The most prevalent bacteria were Escherichia coli in VEOS (n = 9) and staphylococci (coagulase-negative staphylococci and Staphylococcus aureus) (n = 15) in EOS. Case fatality rates were 40% and 13%, respectively. Independent predictive factors for VEOS were clinical chorioamnionitis (odds ratio [OR]: 10.5; 95% confidence interval [CI]: 3.3-33.4) and high maternal age (OR: 1.2; 95% CI: 1.0-1.3), whereas not receiving systemic antibiotic therapy within 2 days of age (OR: 13.6; 95% CI: 3.7-50.2) and receiving nasal continuous positive airway pressure (n-CPAP) support at 24 hours of age (OR: 9.8; 95% CI: 2.5-38.4) independently predicted septicemia after the first day of life.

CONCLUSIONS

Whereas vertically transmitted septicemia was dominated by Gram-negative bacteria, with predictors being exclusively of maternal origin, EOS was dominated by typically nosocomial flora, with n-CPAP treatment at 24 hours of age being a powerful predictor. Early n-CPAP treatment, as opposed to mechanical ventilation, as a powerful predictor of septicemia in the early neonatal period, even with adjustment for early systemic antibiotic treatment, is a new observation among extremely premature infants that warrants additional study.

The periplasmic serine protease inhibitor ecotin protects bacteria against neutrophil elastase

Ecotin is a dimeric periplasmic protein from Escherichia coli that has been shown to inhibit potently many trypsin-fold serine proteases of widely varying substrate specificity. To help elucidate the physiological function of ecotin, we examined the family of ecotin orthologues, which are present in a subset of Gram-negative bacteria. Phylogenetic analysis suggested that ecotin has an exogenous target, possibly neutrophil elastase. Recombinant protein was expressed and purified from E. coli, Yersinia pestis and Pseudomonas aeruginosa, all species that encounter the mammalian immune system, and also from the plant pathogen Pantoea citrea. Notably, the Pa. citrea variant inhibits neutrophil elastase 1000-fold less potently than the other orthologues. All four orthologues are dimeric proteins that potently inhibit (<10 pM) the pancreatic digestive proteases trypsin and chymotrypsin, while showing more variable inhibition (5 pM to 24 microM) of the blood proteases Factor Xa, thrombin and urokinase-type plasminogen activator. To test whether ecotin does, in fact, protect bacteria from neutrophil elastase, an ecotin-deficient strain was generated in E. coli. This strain is significantly more sensitive in cell-killing assays to human neutrophil elastase, which causes increased permeability of the outer membrane that persists even during renewed bacterial growth. Ecotin affects primarily the ability of E. coli to recover and grow following treatment with neutrophil elastase, rather than the actual rate of killing. This suggests that an important part of the antimicrobial mechanism of neutrophil elastase may be a periplasmic bacteriostatic effect of protease that has translocated across the damaged outer membrane.

Spread of Stenotrophomonas maltophilia colonization in a pediatric intensive care unit detected by monitoring tracheal bacterial carriage and molecular typing

In our pediatric intensive care unit in Tours (France), intubated and ventilated inpatients are systematically monitored for tracheal bacterial colonization twice a week. This led us to detect five patients colonized with Stenotrophomonas maltophilia over a 4-month period. Molecular typing of the isolates using random amplified polymorphism DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) confirmed that four of the five isolates were genetically related. The strict isolation of carriers and improvements in hygiene measures stopped the spread. This systematic strategy prevented pulmonary nosocomial infections or allowed their early detection. Moreover, it has made it possible to assess the efficiency of care practices continuously.

Pathology of new bronchopulmonary dysplasia

Technological advances, improved ventilatory strategies and better nursing techniques, coupled with the use of prenatal steroids and postnatal surfactant, have resulted in the survival of smaller and more immature infants. Preterm infants likely to develop bronchopulmonary dysplasia (BPD) are born during the canalicular phase of lung development at 24-26 weeks, a time when alveolar and distal vascular development commences. The histopathologic lesions of severe airway injury and alternating sites of overinflation and fibrosis in 'old' BPD have been replaced in 'new' BPD with the pathologic changes of large, simplified alveolar structures, a dysmorphic capillary configuration and variable interstitial cellularity and/or fibroproliferation. Airway and vascular lesions, when present, tend to occur in infants who over time develop more severe disease. The alveolar and capillary hypoplasia of new BPD will require the development of specific therapies, but avoiding volutrauma, oxidant injury and inflammation/infection will improve lung morphology.

Inflammation and bronchopulmonary dysplasia

Pulmonary inflammation is a key feature in the pathogenesis of bronchopulmonary dysplasia (BPD). This inflammatory process, induced by multiple risk factors, is characterized by the presence of inflammatory cells, cytokines and an arsenal of additional humoral mediators in the airways and pulmonary tissue of preterm infants with the condition. Several mediators have a direct detrimental effect on pulmonary structures by affecting cell integrity and inducing apoptosis. An imbalance between pro-inflammatory and anti-inflammatory factors can generally be considered to be a hallmark of lung injury. Intrauterine exposure to pro-inflammatory cytokines or antenatal infection may prime the fetal lung such that minimally injurious postnatal events provoke an excessive pulmonary inflammatory response that most certainly affects normal alveolization and pulmonary vascular development in preterm infants with BPD.

Microbial infection and inflammation in the development of chronic lung disease of prematurity

Bronchopulmonary dysplasia or chronic lung disease of prematurity is a prolonged respiratory failure with multifactorial etiology in very low birth-weight neonates. This review summarizes current knowledge about the molecular mechanisms of different infections and inflammatory responses that are involved in the development of chronic lung disease of prematurity.

Surveillance of ventilator-associated pneumonia in very-low-birth-weight infants

BACKGROUND

Surveillance of ventilator-associated pneumonia (VAP) is an essential part of quality patient care. Very-low-birth-weight (VLBW) infants, many with tracheal microbial colonization and bronchopulmonary dysplasia (BPD), comprise a difficult group in whom to make a diagnosis of pneumonia with the Centers for Disease Control and Prevention (CDC) criteria for infants younger than 1 year.

OBJECTIVE

Our objective was to retrospectively compare VAP surveillance diagnoses made by the hospital infection control practitioner (ICP) with those made by a panel of experts with the same clinical and laboratory evidence and supportive radiologic data. A secondary objective was to compare radiologic diagnosis of pneumonia made by the general hospital radiologists, by the panel of experts, and by a pediatric radiologist from another hospital.

STUDY POPULATION

Thirty-seven VLBW infants identified as at risk for VAP by the ICP on the basis of a positive bacterial tracheal culture and the application of CDC criteria for the definition of pneumonia were studied.

METHODS

Clinical and laboratory evidence and routine radiologic reports made by the general radiologist were reviewed independently by a panel of experts composed of 3 experienced neonatologists. Chest x-rays from the day before, day of, and day after the surveillance date were reviewed separately by the 3 neonatologists and also by a pediatric radiologist.

RESULTS

After inter-reader reliability was found satisfactory (kappa's coefficient, 0.47-0.75; P <.05), the panel of neonatologists determined that the 37 VLBW infants represented 4 distinct clinical categories. Group 1 comprised 12 airway-colonized infants, aged 14 to 30 days, who on the surveillance date, albeit intubated, were asymptomatic, not treated with antibiotics, and survived. Group 2 comprised 11 airway-colonized infants, aged 7 to 42 days, who presented with equivocal clinical, laboratory, or radiologic signs of VAP and survived. Group 3 comprised 7 airway-colonized infants, aged 14 to 21 days, who were acutely ill (3 died) and had clinical and laboratory evidence of nosocomial bloodstream infection (BSI) but no radiologic signs of pneumonia. Group 4 comprised 7 infants, aged 14 to 28 days, who were acutely ill (4 died) and had clinical and laboratory evidence of infection and radiologic changes consistent with VAP. Radiologic Findings: General radiologists, neonatologists, and the pediatric radiologist agreed that none of the asymptomatic airway-colonized infants (Group 1) had VAP. General radiologists reported signs suggestive of pneumonia in 8 of 11 infants (Group 2), a finding not corroborated by the others. Everybody agreed on the absence of radiologic pneumonia in 6 of 7 patients with nosocomial BSI (Group 3) and on the presence of signs consistent with pneumonia in the remaining 7 infants (Group 4).

CONCLUSION

Surveillance diagnosis of VAP in VLBW infants is difficult because current CDC definitions are not specific for this population. Isolated positive tracheal culture alone does not distinguish between bacterial colonization and respiratory infection. Clinical and laboratory signs of VAP, mostly nonspecific, can be found in other conditions such as bronchopulmonary dysplasia and nosocomial BSI. Routine radiologic reports suggestive of pneumonia in airway-colonized infants without definitive clinical and laboratory evidence of infection could be misleading. To improve accuracy, surveillance diagnosis of VAP in special populations such as VLBW infants should be reformulated; meanwhile, ICPs should seek consultation with experienced clinicians for interpretation of data.

Purulence and gram-negative bacilli in tracheal aspirates of mechanically ventilated very low birth weight infants

OBJECTIVE

Tracheal aspirates (TAs) from mechanically ventilated very low birth weight (VLBW) infants are frequently obtained during the evaluation of suspected sepsis, tracheitis, or ventilator-associated pneumonia (VAP). Purulence and bacteria in Gram stain of bronchopulmonary secretions are considered signs of respiratory infection, and medical decisions are made on the assumption that they are predictors of positive bacterial tracheal cultures (TCs). The purpose of this retrospective investigation was to establish the relationship of purulence and bacteria in TA from ventilated VLBW infants with positive TC and to identify its clinical significance.

STUDY DESIGN

One hundred and seventy consecutively born VLBW infants (1996 to 1998) who remained on mechanical ventilation longer than 1 week were studied. Demographic, laboratory, and clinical data were obtained from hospital medical records. Purulence, defined by the number of polymorphonuclear leukocytes (PMNs) per low power field (LPF), was reported as light (<25 PMNs/LPF) or moderate/heavy (>or=25 PMNs/LPF) for every TA.

RESULTS

Purulence was absent in 469 of 646 (72%) TA taken from 170 infants. Light purulence was present in 17% and moderate/heavy purulence in 11%. TCs were positive in 58% of non-purulent, 94% of light, and 100% of moderate/heavy purulent TA. Bacteria on Gram stain were present in 12% of non-purulent, 70% of light purulent, and 83% of moderate/heavy purulent TA. Moderate/heavy purulence in TA was predictive of a positive TC with Gram-negative bacilli (GNB) with 70% sensitivity, 100% specificity, 100% positive predictive value, and 67% negative predictive value. Purulence in TA, as well as GNB airway colonization, became more frequent as mechanical ventilation progressed and was not associated with a particular GNB species. There were 79 infants who never had purulent TA and 91 who, at some time during the hospitalization, did. At the time of first purulent TA, 65 (71%) of 91 infants were asymptomatic. Twenty-six infants (29%) had clinical deterioration for which they underwent sepsis work-up. Three had blood stream infection, 5 VAP, 5 tracheitis, and 13 respiratory complications of non-infectious etiology. Four of five VAP infants died; all others survived.

CONCLUSION

In VLBW infants, purulence in TA is associated with prolonged endotracheal intubation and is temporally related to GNB airway colonization. At the time of the first purulent TA, the majority of mechanically ventilated VLBW infants are asymptomatic. Only a few symptomatic VLBW infants had nosocomial respiratory infection. Understanding the clinical significance of purulence and GNB in TA from this unique patient population is important for management and prognosis, and it may decrease concern for infection and the associated use of antibiotics.

New insights into the pathogenesis of pulmonary inflammation in preterm infants

Chronic lung disease (CLD) and bronchopulmonary dysplasia are associated with a significant inflammatory response of the airways and the interstitium of the lungs. Besides inflammatory cells, various cytokines, lipid mediators, proteolytic enzymes and toxic oxygen radicals may play an essential role in the pathogenesis of this disease. Intrauterine exposure to chorioamnionitis or proinflammatory cytokines has been shown to induce a pulmonary and systemic inflammatory response in the fetus. In this subgroup, antenatal infection may prime the lung such that minimally injurious postnatal events provoke an excessive inflammatory response in the airways and the pulmonary tissue. Inflammation and lung injury most certainly affect normal alveolization and pulmonary vascular development in preterm infants with CLD.

Molecular epidemiology of methicillin resistant Staphylococcus aureus isolated from newborns in a hospital in Rio de Janeiro, Brazil

Methicillin resistant Staphylococcus aureus (MRSA) is an organism that is frequently transmitted in hospitals and perinatal units. The MRSA is considered a public health problem in neonatology because of its strong potential for dissemination in the wards associated with high rates of morbidity and mortality. In this study we describe the bacteriological, epidemiological and molecular characteristics of MRSA isolated from anterior nares and blood cultures of newborns hospitalized in a public maternity hospital in the city of Rio de Janeiro, Brazil. The frequency of MRSA isolated from nasal swabs of newborns was 47.8% (43/90). The genetic analysis of MRSA strains from anterior nares, showed 8 different pulsed field gel electrophoresis patterns (PFGE). Upon analysis of PFGE patterns of the 12 MRSA strains isolated from blood cultures, 8 different patterns were observed, 9 (75%) strains were genetic related to nasal secretion isolates patterns. In conclusion, our data demonstrate the importance of screening of newborns for the presence of MRSA in Brazilian hospitals and the usefulness of genetic typing of these pathogen during epidemiologic studies. This should lead to a better knowledge on the significancy and spreading of MRSA in the hospitals.

Ventilator-associated pneumonia in very low-birth-weight infants at the time of nosocomial bloodstream infection and during airway colonization with Pseudomonas aeruginosa

PURPOSE

To study retrospectively the incidence of ventilator-associated pneumonia (VAP) at the time of Pseudomonas aeruginosa nosocomial bloodstream infection (BSI) and at the time of P aeruginosa airway colonization.

MATERIALS AND METHODS

Fifteen very low-birth-weight infants who had P aeruginosa BSI and 33 others who did not but who had P aeruginosa airway-colonization were studied. We correlated clinical data, blood cultures (BCs), and tracheal cultures (TCs) with radiologic findings from radio-graphs taken within 2 days before, the day of, and 1 day after BCs or TCs were first positive for P aeruginosa. Chest radiographs were graded by using semiquantitative scores for bronchopulmonary dysplasia and for pneumonia.

RESULTS

Mean birth weight, gestational age, and age when BC or TC became positive were similar for patients with BSI and colonization. At the time of BSI, 2 infants had airway colonization with P aeruginosa; the TCs of the remaining 13 grew P aeruginosa as a new pathogen. Thirteen of 15 patients with BSI, but none of 33 infants with colonization, died within 2 days of positive BC. VAP was diagnosed in 13 of 15 patients with BSI and in 3 of 33 infants with colonization.

CONCLUSION

Mechanically ventilated very low-birth-weight infants whose TCs yield P aeruginosa but whose BCs remain negative infrequently have VAP are presumed airway-colonized and are expected to survive. Conversely, VAP is likely to be found when BCs and TCs simultaneously grow P aeruginosa, and high mortality is anticipated.