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The perfidious effect of topical placebo: calibration of Staphylococcus aureus ventilator-associated pneumonia incidence within selective digestive decontamination studies versus the broader evidence base.

ABSTRACT: Among various methods for preventing ventilator-associated pneumonia (VAP), the evidence base for selective digestive decontamination (SDD) appears most compelling. However, the extent of Staphylococcus aureus emergence with SDD use remains uncertain. Groups from 37 observational studies and component (control and intervention) groups from 58 studies of SDD and other methods of VAP prevention were sourced exclusively from 10 systematic reviews. S. aureus as a proportion of VAP isolates (S. aureus isolate proportion [S. aureus IP]) among component groups was calibrated versus that among observational groups (the benchmark). The influence of topical placebo used for blinding purposes and other group-level factors was estimated using generalized estimating equation methods (GEE). The mean S. aureus IP is 22% (95% confidence interval [CI], 19 to 25) for 37 observational groups versus 32% (24 to 41) and 20% (15 to 25) for 22 control groups from the SDD evidence base which did versus did not receive topical placebo, respectively. In GEE models including all 148 observational and component groups, membership of a control (P = 0.03) or intervention (P < 0.001) group of an SDD study that used topical placebo was associated with higher S. aureus IP, whereas, in contrast, membership of these groups was without effect on Pseudomonas aeruginosa. Topical placebo is implicated as a vehicle for selective cross-infection with S. aureus within the specific context of the SDD evidence base. This effect of topical placebo is perfidious; it could contribute to the higher VAP incidence and inflate the apparent "effectiveness" of SDD. The SDD evidence base requires reappraisal.

SUBMITTER: Hurley JC

PROVIDER: S-EPMC3754294 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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The perfidious effect of topical placebo: calibration of Staphylococcus aureus ventilator-associated pneumonia incidence within selective digestive decontamination studies versus the broader evidence base.

Hurley James C JC

Antimicrobial agents and chemotherapy 20130708 9

Among various methods for preventing ventilator-associated pneumonia (VAP), the evidence base for selective digestive decontamination (SDD) appears most compelling. However, the extent of Staphylococcus aureus emergence with SDD use remains uncertain. Groups from 37 observational studies and component (control and intervention) groups from 58 studies of SDD and other methods of VAP prevention were sourced exclusively from 10 systematic reviews. S. aureus as a proportion of VAP isolates (S. aureu ...[more]

PMID: 23836178

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Project description:IntroductionSelective digestive decontamination (SDD) appears to have a more compelling evidence base than non-antimicrobial methods for the prevention of ventilator associated pneumonia (VAP). However, the striking variability in ventilator associated pneumonia-incidence proportion (VAP-IP) among the SDD studies remains unexplained and a postulated contextual effect remains untested for.MethodsNine reviews were used to source 45 observational (benchmark) groups and 137 component (control and intervention) groups of studies of SDD and studies of three non-antimicrobial methods of VAP prevention. The logit VAP-IP data were summarized by meta-analysis using random effects methods and the associated heterogeneity (tau2) was measured. As group level predictors of logit VAP-IP, the mode of VAP diagnosis, proportion of trauma admissions, the proportion receiving prolonged ventilation and the intervention method under study were examined in meta-regression models containing the benchmark groups together with either the control (models 1 to 3) or intervention (models 4 to 6) groups of the prevention studies.ResultsThe VAP-IP benchmark derived here is 22.1% (95% confidence interval; 95% CI; 19.2 to 25.5; tau2 0.34) whereas the mean VAP-IP of control groups from studies of SDD and of non-antimicrobial methods, is 35.7 (29.7 to 41.8; tau2 0.63) versus 20.4 (17.2 to 24.0; tau2 0.41), respectively (P < 0.001). The disparity between the benchmark groups and the control groups of the SDD studies, which was most apparent for the highest quality studies, could not be explained in the meta-regression models after adjusting for various group level factors. The mean VAP-IP (95% CI) of intervention groups is 16.0 (12.6 to 20.3; tau2 0.59) and 17.1 (14.2 to 20.3; tau2 0.35) for SDD studies versus studies of non-antimicrobial methods, respectively.ConclusionsThe VAP-IP among the intervention groups within the SDD evidence base is less variable and more similar to the benchmark than among the control groups. These paradoxical observations cannot readily be explained. The interpretation of the SDD evidence base cannot proceed without further consideration of this contextual effect.

Project description:ObjectivesTo determine the effect on mortality of selective digestive decontamination, selective oropharyngeal decontamination, and topical oropharyngeal chlorhexidine in adult patients in general intensive care units and to compare these interventions with each other in a network meta-analysis.DesignSystematic review, conventional meta-analysis, and network meta-analysis. Medline, Embase, and CENTRAL were searched to December 2012. Previous meta-analyses, conference abstracts, and key journals were also searched. We used pairwise meta-analyses to estimate direct evidence from intervention-control trials and a network meta-analysis within a Bayesian framework to combine direct and indirect evidence.Inclusion criteriaProspective randomised controlled trials that recruited adult patients in general intensive care units and studied selective digestive decontamination, selective oropharyngeal decontamination, or oropharyngeal chlorhexidine compared with standard care or placebo.ResultsSelective digestive decontamination had a favourable effect on mortality, with a direct evidence odds ratio of 0.73 (95% confidence interval 0.64 to 0.84). The direct evidence odds ratio for selective oropharyngeal decontamination was 0.85 (0.74 to 0.97). Chlorhexidine was associated with increased mortality (odds ratio 1.25, 1.05 to 1.50). When each intervention was compared with the other, both selective digestive decontamination and selective oropharyngeal decontamination were superior to chlorhexidine. The difference between selective digestive decontamination and selective oropharyngeal decontamination was uncertain.ConclusionSelective digestive decontamination has a favourable effect on mortality in adult patients in general intensive care units. In these patients, the effect of selective oropharyngeal decontamination is less certain. Both selective digestive decontamination and selective oropharyngeal decontamination are superior to chlorhexidine, and there is a possibility that chlorhexidine is associated with increased mortality.

Dataset Information

The perfidious effect of topical placebo: calibration of Staphylococcus aureus ventilator-associated pneumonia incidence within selective digestive decontamination studies versus the broader evidence base.

Publications

The perfidious effect of topical placebo: calibration of Staphylococcus aureus ventilator-associated pneumonia incidence within selective digestive decontamination studies versus the broader evidence base.

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