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

Infection, neutrophils, and hematopoietic growth factors in the pathogenesis of neonatal chronic lung disease

Continued definition of the biochemical and molecular mechanisms underlying the development of chronic lung disease (CLD) has persuaded investigators that inflammatory cells and mediators are key factors in the pathophysiology of the disease. High numbers of inflammatory cells and their products are present in the airways of ventilated neonates with respiratory distress syndrome and precede the development of CLD. This article reviews the mechanisms underlying neutrophil recruitment in the lungs of ventilated preterm infants with respiratory distress syndrome and the injurious effects that these cells can produce on lung parenchyma with special emphasis on the development of CLD. The role of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor is stressed as a pivotal mechanism of neutrophil recruitment and activation.

Failure of systemic antibiotics to eradicate gram-negative bacilli from the airway of mechanically ventilated very low-birth-weight infants

BACKGROUND

Gram-negative bacillary (GNB) airway colonization in mechanically ventilated newborns is associated with morbidity and mortality, which may be reduced if systemic antimicrobial therapy eradicates GNB from the airway. Efforts to do so in adults have met with variable success; similar experiences in newborns have not been reported.

METHODS

From 1991 through 1998, 531 very low-birth-weight infants were mechanically ventilated longer than 2 weeks. The study group was 106 infants with GNB airway colonization. Sixty-four other neonates in whom GNB nosocomial bloodstream infections developed served as antibiotic treatment outcome control.

RESULTS

Isolated from the airway were enteric (70 cases) and environmental (36 cases) GNB. Gentamicin alone or with ceftazidime (79), ceftazidime (11), piperacillin in combination with tazobactam or tobramycin (8), and tobramycin, in combination with ampicillin/sulbactam or mezlocillin (8) were the antimicrobials selected. Systemic antibiotics failed to eradicate GNB colonization in 97% of the cases. Six of the 106 infants with airway colonization died for reasons unrelated to infection. Sixty-four infants experienced 67 bloodstream infections as a result of enteric (53) and environmental (14) GNB. Gentamicin alone (23), with ceftazidime (26), or with clindamycin or ampicillin/sulbactam (9), piperacillin with tazobactam or tobramycin (3) and ceftazidime alone (6) were the antimicrobials selected. Survival occurred in 84% of the 67 nosocomial bloodstream infections.

CONCLUSIONS

Systemic antibiotics do not consistently eradicate GNB from the airway of mechanically ventilated newborns, therefore its empirical use for prophylaxis or treatment of airway colonization should be discouraged.

An outbreak of influenza A in a neonatal intensive care unit

OBJECTIVES

Investigation of an outbreak of influenza A in a neonatal intensive care unit (NICU) with examination of risk factors for infection and outcomes.

DESIGN

Retrospective cohort study of infants admitted to the unit during the outbreak period. Prospective survey of NICU staff and mothers of infants in the cohort study.

SETTING

Level III nursery in a university-affiliated tertiary referral center.

RESULTS

Nineteen infants in the NICU were infected with influenza A There were six symptomatic cases and one death who had evidence of virus-associated hemophagocytic syndrome at autopsy. Amantadine prophylaxis was offered to the NICU staff, and amantadine therapy was given to five of the six symptomatic infants. Mechanical ventilation, gestational age, birth weight, Clinical Risk Index for Babies score, and twin pregnancy were associated with acquisition of influenza A on univariate analysis. Mechanical ventilation (odds ratio [OR], 6.2; P=.02) and twin pregnancy (OR, 7.0; P=.04) remained as significant risk factors for infection on multiple logistic regression analysis. Only 15% of respondents to the NICU staff survey were vaccinated against influenza. There was no association between a history of an influenza-like illness during pregnancy and acquisition of influenza A by infants of mothers who responded to the maternal survey (OR, 0.91; P=1.0).

CONCLUSIONS

Influenza A is an important pathogen in the neonatal population and is readily transmissible in the NICU setting.

Enterobacter cloacae outbreak in the NICU related to disinfected thermometers

In the first week ot December 1997, an increasing incidence of neonates colonized with multi-drug resistant Enterobacter cloacae (MR-E. cloacae) was observed in the neonatal Intensive care unit of our 950-bed university hospital. Initially, re-enforcement of infection control practices including hand disinfection and cohort isolation seemed to be sufficient to control the outbreak. Nevertheless, an increasing number of newly admitted patients was paralleled by another rise in the incidence of colonized neonates. Since E. cloacae was initially found in urine specimens of the patients, surveillance and environmental cultures were aimed at procedures and instruments that might colonize the gastro-intestinal and/or urinary tract. E, cloacae was isolated from a single cap of an electronic digital thermometer. Despite banning of this possible source, newly admitted neonates still became colonized. The unit was closed for further admissions and a second round of extensive screening was started; this time including all available thermometers and continuous rectal temperature probes. Ready-to-use 'disinfected thermometers and probes were found to be colonized with MR-E. cloacae. Observation of disinfection procedures and a laboratory investigation revealed that 'rushed disinfection with alcohol 80% led to a 1 in 10 chance of thermometers still being contaminated. Furthermore, alcoholic hand rub used for convenience disinfection failed to disinfect thermometers in 40% and 20% of the cases when done in a 'rushed' or 'careful' fashion, respectively. Adequate disinfection of the thermometers led to the control of the outbreak, with no new occurrence of MR-E. cloacae in the following months.

Prophylaxis against early adrenal insufficiency to prevent chronic lung disease in premature infants

BACKGROUND. Many extremely low birth weight infants (<1000 g) show biochemical evidence of adrenal insufficiency in the first week of life, correlating with subsequent development of chronic lung disease (CLD).

METHODS

We conducted a randomized, double-masked, placebo-controlled pilot study to test whether early treatment with low-dose hydrocortisone for 12 days (1 mg/kg/day for 9 days followed by.5 mg/kg/day for 3 days), begun before 48 hours of life, would increase the likelihood of survival without CLD.

RESULTS

Forty patients were enrolled at two centers. Birth weight and gestation were similar for treatment and placebo groups: 732 +/- 135 g versus 770 +/- 135 g and 25.2 +/- 1.3 weeks versus 25.4 +/- 1.5 weeks. More infants treated with hydrocortisone achieved study success, defined as survival without supplemental oxygen at 36 weeks' postconception (12/20 [60%] vs 7/20 [35%]). Lower birth weight, histologic chorioamnionitis, and preeclampsia were significant risk factors, whereas study center, prenatal steroids, sex, and ethnicity were not significant. Hydrocortisone treatment decreased days on >40% oxygen, days on >25% oxygen, days on ventilator, and oxygen at discharge. Among infants exposed to chorioamnionitis, hydrocortisone treatment also was associated with increased enteral intake during the first month of life and with increased weight at 36 weeks' postconception. Five treated infants and 6 placebo infants developed sepsis; 3 in each group died.

CONCLUSIONS

First, early treatment with low-dose hydrocortisone in this population of extremely low birth weight infants increased the likelihood of survival without CLD. Second, the benefit was particularly apparent in infants with chorioamnionitis. Third, a larger multicenter trial is needed to verify the primary outcome and to better evaluate risks and benefits.

Surfactant proteins A and D in premature baboons with chronic lung injury (Bronchopulmonary dysplasia). Evidence for an inhibition of secretion

Surfactant proteins A and D (SP-A and SP-D) are believed to participate in the pulmonary host defense and the response to lung injury. In order to understand the effects of prematurity and lung injury on these proteins, we measured the amounts of SP-A and SP-D and their mRNAs in three groups of animals: (1) nonventilated premature baboon fetuses; (2) neonatal baboons delivered prematurely at 140 d gestation age (ga) and ventilated with PRN O(2); (3) animals of the same age ventilated with 100% O(2) to induce chronic lung injury. In nonventilated fetuses, tissue and lavage SP-A were barely detectable in baboons of 125 and 140 d ga, but they equaled or exceeded adult SP-A concentrations (g/g lung dry wt) at 175 d (term gestation, 185 d). In contrast, SP-D was readily detectable in tissue and lavage at 125 and 140 d ga. When the baboons of 140 d ga were ventilated for 10 d with 100% oxygen to produce chronic lung injury, the tissue concentration of SP-A was five times greater than that of normal adults; SP-D 16-times greater. Despite the sizable tissue pools of SP-A and SP-D, however, lavage SP-A was only 7% of that of normal adults and lavage SP-D just equaled the amount in normal adults. Nevertheless, because SP-D is normally in much lower concentration than is SP-A, their total comprised less than 12% of the SP-A and SP-D found in the lavage of a healthy adult. The results indicate that in chronic lung injury, SP-A is significantly reduced in the alveolar space. SP-D concentration in lavage is about equal to that in normal adults, possibly because of the 16-fold excess in tissue, but the total collectin pool in lavage is still significantly reduced. Because these collectins may bind and opsonize bacteria and viruses, decrements in their amounts may present additional risk to those premature infants who require prolonged periods of ventilatory support.

Striking differences in the nasopharyngeal flora of healthy Angolan, Brazilian and Dutch children less than 5 years old

Community-acquired pneumonia from enteric gram-negative bacilli is more common in developing than in industrialized countries. We investigated the nasopharyngeal flora in healthy children from Angola, Brazil and The Netherlands to see whether enteric gram-negative bacilli are more often part of the commensal flora in developing countries. Nasopharyngeal specimens were collected from children aged between 4 months and 5 years in day-care centres and immunization clinics. Children who had received antibiotics or were malnourished were excluded. Brazilian and Angolan children had a higher number of household members than Dutch children (5.5 and 7 vs 3.9 mean number of household members, respectively) (p < 0.0001). Enteric and non-fermentative gram-negative bacilli were much more prevalent in Brazilian (50%) and Angolan (57%) children than in Dutch (4%) children (p < 0.0001). By univariate analysis, carriage of enteric gram-negative bacilli was associated with the number of household members (r = 0.26; p < 0.001). The high carriage rate of enteric gram-negative bacilli in children from Angola and Brazil may explain why enteric gram-negative bacilli are a common cause of pneumonia in developing countries.

Bloodstream infections in a neonatal intensive-care unit: 12 years' experience with an antibiotic control program

OBJECTIVE

To assess the prevalence of gram-positive coccal (GPC), gram-negative bacillary (GNB), and fungal blood-stream infections (BSIs) during a 12-year period in which a consistent antibiotic treatment protocol was in place; to evaluate the efficacy of these antibiotic policies in relation to treatment, to the emergence of bacterial or fungal resistance, and to the occurrence of infection outbreaks or epidemics.

STUDY DESIGN

Case series.

METHODS

Demographic, clinical, and bacteriological information from 363 infants born during 1986 through 1991 and 1992 through 1997 who developed 433 blood-culture-proven BSIs was analyzed. Early-onset BSIs were defined as those infections discovered within 48 hours of birth, and late-onset BSIs as those that occurred thereafter. Suspected early-onset BSIs were treated with ampicillin and gentamicin, and suspected late-onset BSIs with vancomycin and gentamicin. Antibiotics were changed on the basis of organism antimicrobial susceptibility.

RESULTS

Early-onset BSIs were noted in 52 of 21,336 live births and 40 of 20,402 live births during 1986 through 1991 and 1992 through 1997, respectively. GPC (83% due to group B streptococcus [GBS]) accounted for approximately one half of early-onset BSI cases and GNB (68% Enterobacteriaceae) for the remainder. Early-onset GBS declined from 24 to 11 cases (P=.04) and late-onset BSI increased from 111 to 230 cases (P<.01) from the first to the last study period. Sixty-eight percent of late-onset BSIs were due to GPC (primarily coagulase-negative Staphylococcus), 18% to GNB, and 14% to fungus. Over the study period, Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa isolated from the newborn intensivecare unit (unlike those strains from other hospital units) remained fully susceptible to ceftazidime and gentamicin. Although the hospitalwide prevalence of methicillin-resistant Staphylococcus aureus increased, all 17 newborn BSI cases were due to methicillin-sensitive strains. Prevalence of methicillin-resistant coagulase-negative Staphylococcus increased, although all strains remained vancomycin-susceptible, as did the 16 Enterococcus faecalis isolates. All fungi recovered (from 48 patients) were susceptible to amphotericin.

CONCLUSION

We observed a decrease in the prevalence of early-onset BSIs due to GBS and an increase in late-onset BSIs due to GPC, GNB, and fungi. The combination of ampicillin and gentamicin for suspected early-onset BSIs and vancomycin and gentamicin for late-onset BSIs has been successful for treatment of individual patients without the occurrence of infection outbreaks or the emergence of resistance. Controlled antibiotic programs and periodic evaluations based on individual unit and not on hospitalwide antibiograms are advisable.