Studies of selective digestive decontamination as a natural experiment to evaluate topical antibiotic prophylaxis and cephalosporin use as population-level risk factors for enterococcal bacteraemia among ICU patients

Rebound Inverts the Staphylococcus aureus Bacteremia Prevention Effect of Antibiotic Based Decontamination Interventions in ICU Cohorts with Prolonged Length of Stay

Could rebound explain the paradoxical lack of prevention effect against Staphylococcus aureus blood stream infections (BSIs) with antibiotic-based decontamination intervention (BDI) methods among studies of ICU patients within the literature? Two meta-regression models were applied, each versus the group mean length of stay (LOS). Firstly, the prevention effects against S. aureus BSI [and S. aureus VAP] among 136 studies of antibiotic-BDI versus other interventions were analyzed. Secondly, the S. aureus BSI [and S. aureus VAP] incidence in 268 control and intervention cohorts from studies of antibiotic-BDI versus that among 165 observational cohorts as a benchmark was modelled. In model one, the meta-regression line versus group mean LOS crossed the null, with the antibiotic-BDI prevention effect against S. aureus BSI at mean LOS day 7 (OR 0.45; 0.30 to 0.68) inverted at mean LOS day 20 (OR 1.7; 1.1 to 2.6). In model two, the meta-regression line versus group mean LOS crossed the benchmark line, and the predicted S. aureus BSI incidence for antibiotic-BDI groups was 0.47; 0.09-0.84 percentage points below versus 3.0; 0.12-5.9 above the benchmark in studies with 7 versus 20 days mean LOS, respectively. Rebound within the intervention groups attenuated and inverted the prevention effect of antibiotic-BDI against S. aureus VAP and BSI, respectively. This explains the paradoxical findings.

Indirect (herd) effects of topical antibiotic prophylaxis and oral care versus non-antimicrobial methods increase mortality among ICU patients: realigning Cochrane review data to emulate a three-tier cluster randomised trial

OBJECTIVE

This study aimed to estimate the direct effects to recipients and indirect (herd) effects to non-recipients of each of topical antibiotic prophylaxis (TAP) and oral care methods on patient mortality within randomised concurrent controlled trials (RCCT) using Cochrane review data.

DESIGN

Control and intervention groups from 209 RCCTs of TAP (tier 3), oral care (tier 2) each versus non-antimicrobial (tier 1) ventilator-associated pneumonia (VAP) prevention interventions arranged to emulate a three-tiered cluster randomised trial (CRT). Eligible RCCTs were those including ICU patients with >50% of patients receiving >24 hours of mechanical ventilation (MV) with mortality data available as abstracted in 13 Cochrane reviews.

EXPOSURES

Direct and indirect exposures to either TAP or oral care within RCCTs versus non-antimicrobial VAP prevention interventions.

MAIN OUTCOMES AND MEASURES

The ICU mortality within control and intervention groups, respectively, within RCCTs of either TAP or oral care versus that within non-antimicrobial VAP prevention RCCTs serving as benchmark.

RESULTS

The ICU mortality was 23.9%, 23.0% and 20.3% for intervention groups and 28.7%, 25.5% and 19.5% for control groups of RCCTs of TAP (tier 1), oral care (tier 2) and non-antimicrobial (tier 3) methods of VAP prevention, respectively. In a random effects meta-regression including late mortality data and adjusting for group mean age, year of study publication and MV proportion, the direct effect of TAP and oral care versus non-antimicrobial methods were 1.04 (95% CI 0.78 to 1.30) and 1.1 (95% CI 0.77 to 1.43) whereas the indirect effects were 1.39 (95% CI 1.03 to 1.74) and 1.26 (95% CI 0.89 to 1.62), respectively.

CONCLUSIONS

Indirect (herd) effects from TAP and oral care methods on mortality are stronger than the direct effects as made apparent by the three-tiered CRT. These indirect effects, being harmful to concurrent control groups by increasing mortality, perversely inflate the appearance of benefit within RCCTs.

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.

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.

Candida and the Gram-positive trio: testing the vibe in the ICU patient microbiome using structural equation modelling of literature derived data

Background

Whether Candida interacts with Gram-positive bacteria, such as Staphylococcus aureus, coagulase negative Staphylococci (CNS) and Enterococci, to enhance their invasive potential from the microbiome of ICU patients remains unclear. Several effective anti-septic, antibiotic, anti-fungal, and non-decontamination based interventions studied for prevention of ventilator associated pneumonia (VAP) and other ICU acquired infections among patients receiving prolonged mechanical ventilation (MV) are known to variably impact Candida colonization. The collective observations within control and intervention groups from numerous ICU infection prevention studies enables tests of these postulated microbial interactions in the clinical context.

Methods

Four candidate generalized structural equation models (GSEM), each with Staphylococcus aureus, CNS and Enterococci colonization, defined as latent variables, were confronted with blood culture and respiratory tract isolate data derived from 460 groups of ICU patients receiving prolonged MV from 283 infection prevention studies.

Results

Introducing interaction terms between Candida colonization and each of S aureus (coefficient + 0.40; 95% confidence interval + 0.24 to + 0.55), CNS (+ 0.68; + 0.34 to + 1.0) and Enterococcal (+ 0.56; + 0.33 to + 0.79) colonization (all as latent variables) improved the fit for each model. The magnitude and significance level of the interaction terms were similar to the positive associations between exposure to topical antibiotic prophylaxis (TAP) on Enterococcal (+ 0.51; + 0.12 to + 0.89) and Candida colonization (+ 0.98; + 0.35 to + 1.61) versus the negative association of TAP with S aureus (− 0.45; − 0.70 to − 0.20) colonization and the negative association of anti-fungal exposure and Candida colonization (− 1.41; − 1.6 to − 0.72).

Conclusions

GSEM modelling of published ICU infection prevention data enables the postulated interactions between Candida and Gram-positive bacteria to be tested using clinically derived data. The optimal model implies interactions occurring in the human microbiome facilitating bacterial invasion and infection. This interaction might also account for the paradoxically high bacteremia incidences among studies of TAP in ICU patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12982-022-00116-9.

GSEM modelling of published ICU infection prevention data from > 250 studies enables a test of and provides support to the interaction between Candida and Gram-positive bacteria.

The various ICU infection prevention interventions may each broadly impact the patient microbiome.

Selective digestive decontamination, a seemingly effective regimen with individual benefit or a flawed concept with population harm?

Selective digestive decontamination (SDD) regimens, variously constituted with topical antibiotic prophylaxis (TAP) and protocolized parenteral antibiotic prophylaxis (PPAP), appear highly effective for preventing ICU-acquired infections but only within randomized concurrent control trials (RCCT's). Confusingly, SDD is also a concept which, if true, implies population benefit. The SDD concept can finally be reified  in humans using the broad accumulated evidence base, including studies of TAP and PPAP that used non-concurrent controls (NCC), as a natural experiment. However, this test implicates overall population harm with higher event rates associated with SDD use within the ICU context.

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.

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.

Discrepancies in Control Group Mortality Rates Within Studies Assessing Topical Antibiotic Strategies to Prevent Ventilator-Associated Pneumonia: An Umbrella Review

Supplemental Digital Content is available in the text.

Objectives:

To test the postulate that concurrent control patients within ICUs studying topical oropharyngeal antibiotics to prevent ventilator-associated pneumonia and mortality would experience spillover effects from the intervention.

Data Sources:

Studies cited in 15 systematic reviews of various topical antibiotic and other infection prevention interventions among ICU patients.

Study Selection:

Studies of topical antibiotics, stratified into concurrent control versus nonconcurrent control designs. Studies of nondecontamination-based infection prevention interventions provide additional points of reference. Studies with no infection prevention intervention provide the mortality benchmark. Data from additional studies and data reported as intention to treat were used within sensitivity tests.

Data Extraction:

Mortality incidence proportion data, mortality census, study characteristics, group mean age, ICU type, and study publication year.

Data Synthesis:

Two-hundred six studies were included. The summary effect sizes for ventilator-associated pneumonia and mortality prevention derived in the 15 systematic reviews were replicated. The mean ICU mortality incidence for concurrent control groups of topical antibiotic studies (28.5%; 95% CI, 25.0–32.3; n = 41) is higher versus the benchmark (23.7%; 19.2–28.5%; n = 34), versus nonconcurrent control groups (23.5%; 19.3–28.3; n = 14), and versus intervention groups (24.4%; 22.1–26.9; n = 62) of topical antibiotic studies. In meta-regression models adjusted for group-level characteristics such as group mean age and publication year, concurrent control group membership within a topical antibiotic study remains associated with higher mortality (p = 0.027), whereas other group memberships, including membership within an antiseptic study, are each neutral (p = not significant).

Conclusions:

Within topical antibiotic studies, the concurrent control group mortality incidence proportions are inexplicably high, whereas the intervention group mortality proportions are paradoxically similar to a literature-derived benchmark. The unexplained ventilator-associated pneumonia and mortality excess in the concurrent control groups implicates spillover effects within studies of topical antibiotics. The apparent ventilator-associated pneumonia and mortality prevention effects require cautious interpretation.

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.