Estimating the herd effects of anti-microbial-based decontamination (ABD) interventions on intensive care unit (ICU) acquired bloodstream infections: a deductive meta-analysis.

objectiveTo estimate the herd effects of anti-microbial-based decontamination (ABD) interventions on bloodstream infections (BSIs) among groups of intensive care unit (ICU) patients in relation to group mean length of stay (LOS). To deduce which of three competing hypotheses of ABD effect mediation best accounts for the observed effects.

designArms-based meta-regression of ICU-acquired BSI incidence against group mean LOS for control and interventions arms of ABD and non-ABD controlled trials each versus that in arms of observational studies. EXPOSURES: Within controlled trials of ABD, intervention, concurrent control (CC) and non-concurrent (NCC) groups are directly, indirectly and non-exposed, respectively. MAIN OUTCOMES AND MEASURES: BSI incidence, both overall and for BSI subtypes.

resultsIn the arms-based meta-regression, the predicted BSI incidence per 100 patients in the ABD intervention arms increased from 4.6 (95% CI 3.8 to 5.5) at mean LOS 7 days to 13.0 (10.4-16.0) at mean LOS 20 days (n=60 arms) and CC arms 8.5 (6.7-11.0) increasing to 19.3 (14.8-24.8; n=52). These increases were double those in the observational (7.2; 6.1-8.5 increasing to 12.9; 10.4-16.7; n=99) and NCC arms and non-ABD arms. These results triangulate with the notional effect size observed in contrast-based meta-analyses.

conclusionsThe increased tempo of BSI acquisition, both overall and for various BSI subtypes, within intervention and CC groups of ABD randomised concurrent controlled trials versus other groups implicate rebound and spillover, respectively. Mechanisms other than colonisation resistance mediate ABD effects.