Unusually High Incidences of Staphylococcus aureus Infection within Studies of Ventilator Associated Pneumonia Prevention Using Topical Antibiotics: Benchmarking the Evidence Base

Prevalence of virulence- and antibiotic resistance-associated genotypes and phenotypes in Staphylococcus aureus strains from the food sector compared to clinical and cow mastitis isolates

Background

Infections by the pathogen Staphylococcus aureus currently represent one of the most serious threats to human health worldwide, especially due to the production of enterotoxins and the ability to form biofilms. These structures and the acquisition of antibiotic resistance limit the action of antibiotics and disinfectants used to combat this microorganism in the industry and the clinic.

Methods

This work reports a comparative phenotypic and genotypic study of 18 S. aureus strains from different origins: clinical samples, milk from mastitic cows and food industry surfaces, most of which were isolated in Northern Spain.

Results

Genetically, the strains were very diverse but, in most cases, a closer proximity was observed for those from the same source. Notably, the average number of virulence genes was not significantly different in strains from the food sector. Of the 18 strains, 10 coded for at least one enterotoxin, and four of them carried 6 or 7 enterotoxin genes. The latter were all veterinary or clinical isolates. Most strains carried prophages, plasmids and/or pathogenicity islands. Regarding antibiotic resistance, although phenotypically all strains showed resistance to at least one antibiotic, resistance genes were only identified in 44.5% of strains, being mastitis isolates those with the lowest prevalence. Virulence-related phenotypic properties such as haemolytic activity, staphyloxanthin production, biofilm-forming capacity and spreading ability were widely distributed amongst the isolates.

Conclusions

Our results indicate that production of virulence factors, antibiotic resistance and biofilm formation can be found in S. aureus isolates from diverse environments, including the food industry, although some of these traits are more prevalent in strains isolated from infections in cows or humans. This emphasizes on the importance of monitoring the spread of these determinants not only in samples from the clinical environment, but also along the food chain, a strategy that falls under the prism of a one-health approach.

Establishing the safety of selective digestive decontamination within the ICU population: a bridge too far?

BACKGROUND

Infection prevention interventions within the intensive care unit (ICU) setting, whether studied within quality improvement projects or cluster randomized trials (CRT), are seen as low risk and grounded in an ethical imperative. Selective digestive decontamination (SDD) appears highly effective at preventing ICU infections within randomized concurrent control trials (RCCTs) prompting mega-CRTs with mortality as the primary endpoint.

FINDINGS

Surprisingly, the summary results of RCCTs versus CRTs differ strikingly, being respectively, a 15-percentage-point versus a zero-percentage-point ICU mortality difference between control versus SDD intervention groups. Multiple other discrepancies are equally puzzling and contrary to both prior expectations and the experience within population-based studies of infection prevention interventions using vaccines. Could spillover effects from SDD conflate the RCCT control group event rate differences and represent population harm? Evidence that SDD is fundamentally safe to concurrent non-recipients in ICU populations is absent. A postulated CRT to realize this, the SDD Herd Effects Estimation Trial (SHEET), would require > 100 ICUs to achieve sufficient statistical power to find a two-percentage-point mortality spillover effect. Moreover, as a potentially harmful population-based intervention, SHEET would pose novel and insurmountable ethical issues including who is the research subject; whether informed consent is required and from whom; whether there is equipoise; the benefit versus the risk; considerations of vulnerable groups; and who should be the gatekeeper?

CONCLUSION

The basis for the mortality difference between control and intervention groups of SDD studies remains unclear. Several paradoxical results are consistent with a spillover effect that would conflate the inference of benefit originating from RCCTs. Moreover, this spillover effect would constitute to herd peril.

Staphylococcus aureus hitchhiking from colonization to bacteremia via Candida within ICU infection prevention studies: a proof of concept modelling

Whether Candida within the patient microbiome drives the pathogenesis of Staphylococcus aureus bacteremia, described as microbial hitchhiking, cannot be directly studied. Group-level observations from studies of various decontamination and non-decontamination-based ICU infection prevention interventions and studies without study interventions (observational groups) collectively enable tests of this interaction within causal models. Candidate models of the propensity for Staphylococcus aureus bacteremia to arise with versus without various antibiotic, anti-septic, and antifungal exposures, each identified as singleton exposures, were tested using generalized structural equation modelling (GSEM) techniques with Candida and Staphylococcus aureus colonization appearing as latent variables within the models. Each model was tested by confrontation against blood and respiratory isolate data, obtained from 467 groups within 284 infection prevention studies. Introducing an interaction term between Candida colonization and Staphylococcus aureus colonization substantially improved GSEM model fit. Model-derived coefficients for singular exposure to anti-septic agents (- 1.28; 95% confidence interval; - 2.05 to - 0.5), amphotericin (- 1.49; - 2.3 to - 0.67), and topical antibiotic prophylaxis (TAP; + 0.93; + 0.15 to + 1.71) as direct effects versus Candida colonization were similar in magnitude but contrary in direction. By contrast, the coefficients for singleton exposure to TAP, as with anti-septic agents, versus Staphylococcus colonization were weaker or non-significant. Topical amphotericin would be predicted to halve both candidemia and Staphylococcus aureus bacteremia incidences versus literature derived benchmarks for absolute differences of < 1 percentage point. Using ICU infection prevention data, GSEM modelling validates the postulated interaction between Candida and Staphylococcus colonization facilitating bacteremia.

Intermittent versus continuous control of tracheal cuff pressure in patients undergoing mechanical ventilation: A systematic review and meta-analysis

AIMS AND OBJECTIVES

To evaluate the effects and safety of intermittent versus continuous control of cuff pressure in patients with mechanical ventilation.

BACKGROUND

Tracheal cuff pressure management is vital to the prognosis of patients with mechanical ventilation.

DESIGN

A meta-analysis.

METHODS

This meta-analysis was conducted and reported according to the PRISMA checklist. We searched Pubmed, Embase, The Cochrane Library, BMJ Best Practice, Web of Science, ProQuest Dissertations, as well as the Chinese Biomedical Literature Database, Wanfang, and China national knowledge infrastructure databases up to 5 August 2022 for randomised controlled trials (RCTs) on the intermittent versus continuous control of cuff pressure. Review Manager 5.3 software was used for relevant data analysis.

RESULTS

A total of 18 RCTs involving 1998 patients with mechanical ventilation were included. The synthesised outcomes indicated that continuous control of cuff pressure is beneficial to reduce the incidence of ventilator-associated pneumonia (VAP) [RR = 0.41, 95%CI (0.35, 0.49)], aspiration [RR = 0.36, 95%CI (0.21, 0.63)], duration of mechanical ventilation [MD = -3.23, 95%CI (-4.66, -1.79)], length of ICU stay [MD = -4.12, 95%CI (-5.40, -2.83)], and increase the volume of subglottic drainage [MD = 18.54, 95%CI (16.50, 20.58)]. There was no significant difference in the mortality between two groups [RR = 1.01, 95%CI (0.84, 1.21)]. Egger regression analyses showed that there were no obvious publication biases in the synthesised results (all p > .05).

CONCLUSIONS

Existing evidence shows that compared with intermittent monitoring of cuff pressure, continuous monitoring of cuff pressure can reduce the occurrence of aspiration and VAP, shorten the patient's duration of mechanical ventilation and length of ICU stay.

RELEVANCE TO CLINICAL PRACTICE

Continuous monitoring of cuff pressure is more beneficial and should be promoted in clinical nursing care of patients undergoing mechanical ventilation.

Structural equation modelling the impact of antimicrobials on the human microbiome. Colonization resistance versus colonization susceptibility as case studies

The impact of antimicrobials on the human microbiome and its relationship to human health are of great interest. How antimicrobial exposure might drive change within specific constituents of the microbiome to effect clinically relevant endpoints is difficult to study. Clinical investigation of each step within a network of causation would be challenging if done 'step-by-step'. An analytic tool of great potential to clinical microbiome research is structural equation modelling (SEM), which has a long history of applications to research questions arising within subject areas as diverse as psychology and econometrics. SEM enables postulated models based on a network of causation to be tested en bloc by confrontation with data derived from the literature. Case studies for the potential application of SEM techniques are colonization resistance (CR) and its counterpart, colonization susceptibility (CS), wherein specific microbes within the microbiome are postulated to either impede (CR) or facilitate (CS) invasive infection with pathogenic bacteria. These postulated networks have three causation steps: exposure to specific antimicrobials are key drivers, clinically relevant infection endpoints are the measurable observables and the activity of key microbiome constituents mediating CR or CS, which may be unobservable, appear as latent variables in the model. SEM methods have potential application towards evaluating the activity of specific antimicrobial agents within postulated networks of causation using clinically derived data.

Asymmetric Effects of Decontamination Using Topical Antibiotics for the ICU Patient

There are several antiseptic, antibiotic and non-decontamination-based interventions for preventing intensive care unit (ICU) acquired infection. These have been evaluated in >200 studies. Infection prevention using topical antibiotic prophylaxis (TAP) appears to be the most effective. Whether antibiotic use in the ICU may influence the risk of infection among concurrent control patients within the same ICU and result in asymmetrical herd effects cannot be resolved with individual studies examined in isolation. The collective observations within control and intervention groups from numerous ICU infection prevention studies simulates a multi-center natural experiment enabling the herd effects of antibiotics to be evaluated. Among the TAP control groups, the incidences for both ventilator associated pneumonia (VAP) and mortality are unusually high in comparison to literature-derived benchmarks. Paradoxically, amongst the TAP intervention groups, the incidences of mortality are also unusually high and the VAP incidences are similar (i.e., not lower) compared to the incidences among studies of other interventions. By contrast, the mortality incidences among the intervention groups of other studies are similar to those among the intervention groups of TAP studies. Using topical antibiotics to prevent infections acquired within the ICU environment may result in profoundly asymmetrical effects.

Is selective decontamination (SDD/SOD) safe in the ICU context?

Multiple individual studies of selective digestive decontamination/selective oropharyngeal decontamination (SDD/SOD) among ICU patients appear to show potent infection prevention effects. Surprisingly, the event rates for multiple endpoints including ventilator-associated pneumonia, bacteraemia and candidaemia among concurrent control groups within SDD/SOD studies appear unusually high versus other rates in the literature. These paradoxical observations raise concern that the contextual effects of SDD/SOD, as postulated in the original SDD/SOD study, not only exist but also are strong. Until these effects are addressed within an optimally designed study, the safety of SDD/SOD within the 'whole of ICU' remains questionable.

Crosstalk Between Lung and Extrapulmonary Organs in Infection and Inflammation

Acute and chronic lung inflammation is a risk factor for various diseases involving lungs and extrapulmonary organs. Intercellular and interorgan networks, including crosstalk between lung and brain, intestine, heart, liver, and kidney, coordinate host immunity against infection, protect tissue, and maintain homeostasis. However, this interaction may be counterproductive and cause acute or chronic comorbidities due to dysregulated inflammation in the lung. In this chapter, we review the relationship of the lung with other key organs during normal cell processes and disease development. We focus on how pneumonia may lead to a systemic pathophysiological response to acute lung injury and chronic lung disease through organ interactions, which can facilitate the development of undesirable and even deleterious extrapulmonary sequelae.

Evaluation of pneumonia due to mechanical ventilation and its association with the severity of disease in patients admitted to intensive care unit

Among the hospital-acquired infections, ventilator-associated pneumonia (VAP) has the highest mortality and morbidity rates. The aim of this study was to identify VAP in the intensive care unit (ICU) and its association with the severity of the disease. This descriptive-analytic study was conducted in Golestan University of Medical Sciences (Northern Iran). In the present study, 239 patients undergoing mechanical ventilation hospitalized in ICU were selected through non-random sampling. Data were recorded by using APACHE II criteria and diagnosis of VAP was made based on clinical criterion and physician confirmation. Data were analyzed by independent t-test, Chi-square test, Mann-Whitney test, and single-variable logistic test. The incidence of VAP was 19.2% and it was significantly related to mean arterial pressure (P = 0.035) and male sex (P = 0.122). There was a significant and direct correlation between the incidence of VAP and the increase in the value of gastric residual volume > 200 ml (P = 0.001). The findings of this study showed that male sex, increased arterial pressure, and gastric residual volume were the risk factors for the development of of VAP.

Structural equation modeling the "control of gut overgrowth" in the prevention of ICU-acquired Gram-negative infection

BACKGROUND

Conceptually, the "control of gut overgrowth" (COGO) is key in mediating prevention against infection with Gram-negative bacilli by topical antibiotic prophylaxis, a common constituent of selective digestive decontamination (SDD) regimens. However, the relative importance of the other SDD components, enteral and protocolized parenteral antibiotic prophylaxis, versus other methods of infection prevention and versus other contextual exposures cannot be resolved within individual studies.

METHODS

Seven candidate generalized structural equation models founded on COGO concepts were confronted with Pseudomonas and Acinetobacter bacteremia as well as ventilator-associated pneumonia data derived from > 200 infection prevention studies. The following group-level exposures were included in the models: use and mode of antibiotic prophylaxis, anti-septic and non-decontamination methods of infection prevention; proportion receiving mechanical ventilation; trauma ICU; mean length of ICU stay; and concurrency versus non-concurrency of topical antibiotic prophylaxis study control groups.

RESULTS

In modeling Pseudomonas and Acinetobacter gut overgrowth as latent variables, anti-septic interventions had the strongest negative effect against Pseudomonas gut overgrowth but no intervention was significantly negative against Acinetobacter gut overgrowth. Strikingly, protocolized parenteral antibiotic prophylaxis and concurrency each have positive effects in the model, enteral antibiotic prophylaxis is neutral, and Acinetobacter bacteremia incidences are high within topical antibiotic prophylaxis studies, moreso with protocolized parenteral antibiotic prophylaxis exposure. Paradoxically, topical antibiotic prophylaxis (moreso with protocolized parenteral antibiotic prophylaxis) appears to provide the strongest summary prevention effects against overall bacteremia and overall VAP.

CONCLUSIONS

Structural equation modeling of published Gram-negative bacillus infection data enables a test of the COGO concept. Paradoxically, Acinetobacter and Pseudomonas bacteremia incidences are unusually high among studies of topical antibiotic prophylaxis.

Incidence of coagulase-negative staphylococcal bacteremia among ICU patients: decontamination studies as a natural experiment

The epidemiology of coagulase-negative staphylococcal (CNS) bacteremia among adult ICU patients remains unclear. Decontamination studies among ICU patients provide a unique opportunity to study the impacts of different diagnostic criteria, exposure to various decontamination interventions, and various other factors, on its incidence over three decades. Decontamination studies among ICU patients reporting CNS bacteremia incidence data were obtained mostly from recent systematic reviews. The CNS bacteremia incidence within component (control and intervention) groups of decontamination studies was benchmarked versus studies without intervention (observational groups). The impacts of antibiotic versus chlorhexidine decontamination interventions, control group concurrency, publication year, and diagnostic criteria were examined in meta-regression models. Among non-intervention (observational) studies which did versus did not specify stringent (≥ 2 positive blood cultures) diagnostic criteria, the mean CNS bacteremia incidence per 100 patients (and 95% CI; n) is 1.3 (0.9–2.0; n = 23) versus 3.6 (1.8–6.9; n = 8), respectively, giving an overall benchmark of 1.8 (1.2–2.4; n = 31). Versus the benchmark incidence, the mean incidence is high among concurrent control (5.7; 3.6–9.1%) and intervention (5.2; 3.6–6.9%), but not non-concurrent control (1.0; 0.4–3.9%) groups of 21 antibiotic studies, nor among eleven component groups of chlorhexidine studies. This high incidence remained apparent (p < 0.01) in meta-regression models adjusting for group wide factors such as diagnostic criteria and publication year. The incidence of CNS bacteremia within both intervention and concurrent (but not non-concurrent) control groups of antibiotic-based decontamination studies are unusually high even accounting for variable diagnostic criteria and other factors.

Infections after a traumatic brain injury: The complex interplay between the immune and neurological systems

Traumatic brain injury (TBI) is a serious global health issue, being the leading cause of death and disability for individuals under the age of 45, and one of the largest causes of global neurological disability. In addition to the brain injury itself, it is increasingly appreciated that a TBI may also alter the systemic immune response in a way that renders TBI patients more vulnerable to infections in the acute post-injury period. Such infections pose an additional challenge to the patient, increasing rates of mortality and morbidity, and worsening neurological outcomes. Hospitalization, surgical interventions, and a state of immunosuppression induced by injury to the central nervous system (CNS), may all contribute to the high rate of infections seen in the population with TBI. Ongoing research to better understand the immunomodulators that underlie TBI-induced immunosuppression may aid in the development of effective therapeutic strategies to improve the recovery trajectory for patients. This review first describes the clinical scenario, posing the question of whether TBI patients are more susceptible to infections such as pneumonia, and if so, why? We then consider how cross-talk between the injured brain and the systemic immune system occurs, and further, how the additional immune challenge of an acquired infection can contribute to ongoing neuroinflammation and neurodegeneration after a TBI. Experimental models combining TBI with infection are discussed, as well as current treatment options available for this double-barreled insult. The aims of this review are to summarize current understanding of the bidirectional relationship between the CNS and the immune system when faced with a mechanical trauma combined with a concomitant infection, and to highlight key outstanding questions that remain in the field.

Unusually High Incidences of Pseudomonas Bacteremias Within Topical Polymyxin-Based Decolonization Studies of Mechanically Ventilated Patients: Benchmarking the Literature

Background

Topical polymyxin (PM)–based regimens to decolonize patients receiving prolonged mechanical ventilation (MV) have been widely studied. However, paradoxical bacteremia incidences remain unexplained.

Methods

The literature was searched for studies of topical PM–based regimens used to decontaminate MV patients reporting incidences of overall and Pseudomonas bacteremia data. In addition, observational groups without any intervention and trials of various interventions other than topical PM (non-PM studies) served to provide external benchmarks and additional points of reference, respectively. The bacteremia incidences were extracted from the control and intervention (component) groups of these studies and compared with metaregression using generalized estimating equation methods.

Results

The summary odds ratio derived from studies of topical PM–based interventions against overall bacteremia was 0.60 (95% confidence interval [CI], 0.53–0.69). Benchmark incidences per 100 MV patients for overall (mean, 8.9%; 95% CI, 6.9% to 10.9%) and Pseudomonas (mean, 0.7%; 95% CI, 0.5% to 1.1%) bacteremia were derived from 16 observational studies. By contrast, among 17 studies of topical PM, the mean incidences among control groups for overall (mean, 15.3%; 95% CI, 11.5% to 20.3%) and Pseudomonas (mean, 1.6%; 95% CI, 0.9% to 3.1%) bacteremia were both higher, whereas these incidences in the intervention groups for both topical PM and non-PM studies were in each case more similar to the respective benchmarks. These paradoxical incidences cannot readily be explained in metaregression models.

Conclusions

Paradoxically, despite an apparent prevention effect of topical PM–based methods against bacteremia overall, the incidences of Pseudomonas bacteremia within the component groups of these studies are unusually high vs literature-derived benchmarks.

Incidences of Pseudomonas aeruginosa-Associated Ventilator-Associated Pneumonia within Studies of Respiratory Tract Applications of Polymyxin: Testing the Stoutenbeek Concurrency Postulates

Regimens containing topical polymyxin appear highly effective at preventing ventilator-associated pneumonia (VAP) overall and, more so, VAP caused by Gram-negative bacteria. However, Stoutenbeek's postulates that VAP incidences within studies of topical antibiotics depend on the context of whether the component (control and intervention) groups of each study were concurrent versus nonconcurrent remain untested. The literature was searched for concurrent control (CC) versus nonconcurrent control (NCC) designed studies of respiratory tract applications of topical polymyxin to mechanically ventilated (MV) patients that reported incidences of Pseudomonas-associated ventilator-associated pneumonia (PsVAP). Studies of various interventions other than topical polymyxin (nonpolymyxin studies) served to provide additional points of reference. The PsVAP incidences within the component groups of all studies were benchmarked against groups from observational studies. This was undertaken by meta-regression using generalized estimating equation methods. Dot plots, caterpillar plots, and funnel plots enable visual benchmarking. The PsVAP benchmark (and 95% confidence interval [CI]) derived from 102 observational groups is 4.6% (4.0 to 5.3%). In contrast, the mean PsVAP within NCC polymyxin intervention groups (1.6%; CI, 1.0 to 4.5%) is lower than that of all other component group categories. The mean PsVAP within CC polymyxin control groups (9.9%; CI, 7.6 to 12.8%) is higher than that of all other component group categories. The PsVAP incidences of control and intervention groups of studies of respiratory tract applications of polymyxin are dependent on whether the groups were within a concurrent versus nonconcurrent study. Stoutenbeek's concurrency postulates are validated.

World-Wide Variation in Incidence of Staphylococcus aureus Associated Ventilator-Associated Pneumonia: A Meta-Regression

Staphylococcus aureus (S. aureus) is a common Ventilator-Associated Pneumonia (VAP) isolate. The objective here is to define the extent and possible reasons for geographic variation in the incidences of S. aureus-associated VAP, MRSA-VAP and overall VAP. A meta-regression model of S. aureus-associated VAP incidence per 1000 Mechanical Ventilation Days (MVD) was undertaken using random effects methods among publications obtained from a search of the English language literature. This model incorporated group level factors such as admission to a trauma ICU, year of publication and use of bronchoscopic sampling towards VAP diagnosis. The search identified 133 publications from seven worldwide regions published over three decades. The summary S. aureus-associated VAP incidence was 4.5 (3.9–5.3) per 1000 MVD. The highest S. aureus-associated VAP incidence is amongst reports from the Mediterranean (mean; 95% confidence interval; 6.1; 4.1–8.5) versus that from Asian ICUs (2.1; 1.5–3.0). The incidence of S. aureus-associated VAP varies by up to three-fold (for the lowest versus highest incidence) among seven geographic regions worldwide, whereas the incidence of VAP varies by less than two-fold. Admission to a trauma unit is the most important group level correlate for S. aureus-associated VAP.