Impact of Multifaceted Interventions Including Waterless Patient Care on Endemic Occurrence of <i>Serratia marcescens</i> in an Intensive Care Unit

<i>Serratia marcescens</i> acquisition is a common problem in intensive care units (ICUs). Following an initial outbreak in 2017 with ongoing endemicity, this study aimed to analyze the impact of behavioral interventions and sink removals on <i>S. marcescens</i> incidence in a tertiary-care ICU. We conducted a quasi-experimental, interventional study including patients with a positive screening or clinical culture for <i>S. marcescens</i> , from 48 h (D2) after ICU admission to 14 days after ICU discharge. A sub-analysis considered patients positive for <i>S. marcescens</i> from ICU admission (D0) to 14 days after ICU discharge. Multivariate Poisson regression analyses were performed. Between January 2014 and December 2022, 167 cases of <i>S. marcescens</i> infection or colonization were identified (respiratory samples, 71%). Despite the presence of an aquatic reservoir, we found that neither behavioral nor architectural interventions (sink removal) reduced significantly <i>S. marcescens</i> incidence, yielding incidence ratios of 1.02 [95%CI 0.33-3.11] and 4.25 [95%CI 0.59-30.56], respectively. However, an association was observed with administration of selective oral decontamination (SOD) in the sub-cohort (OR 1.01; 95%CI 1.00-1.03). Behavioral change interventions and transition to a waterless ICU did not control endemic, polyclonal <i>S. marcescens</i> occurrence. The selective pressure exercised by SOD may have reduced the effectiveness of waterless care.