Outbreaks of Serratia marcescens in neonatal and pediatric intensive care units: Clinical aspects, risk factors and management

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Abstract

The following recommendations are derived from a systematic analysis of 34 Serratia marcescens outbreaks described in 27 publications from neonatal and pediatric intensive care units (NICU, PICU), in which genotyping methods were used to confirm or exclude clonality.

The clinical observation of two or more temporally related cases of nosocomial S. marcescens infection should raise the suspicion of an outbreak, particularly in the NICU or PICU setting. Since colonized or infected patients represent the most important reservoir for cross transmission, hygienic barrier precautions (contact isolation/cohortation, the use of gloves and gowns in addition to strictly performed hand disinfection, enhanced environmental disinfection) should immediately be implemented and staff education given. Well-planned sampling of potential environmental sources should only be performed when these supervised barrier precautions do not result in containment of the outbreak. The current strategy of empiric antibiotic treatment should be reevaluated by a medical microbiologist or an infectious disease specialist. Empiric treatment of colonized children should use combination therapy informed by in vitro susceptibility data; in this context the high propensity of S. marcescens to cause meningitis and intracerebral abscess formation should be considered.

In vitro susceptibility patterns do not reliably prove or exclude the clonality of the outbreak isolate. Genotyping of the isolates by pulse-field gel electrophoresis or PCR-based methods should be performed, but any interventions to interrupt further nosocomial spread should be carried out without waiting for the results.

Introduction

Serratia marcescens, a Gram-negative bacterium, has been described as an important opportunistic pathogen in neonatal (NICI) and pediatric (PICU) intensive care units. According to the European collaborative study of Raymond et al. (Raymond and Aujard, 2000), S. marcescens accounted for 5% and 15% of all culture-positive nosocomial infections in PICUs and in NICUs, respectively. In a case control study from an Italian PICU (Foglia et al., 2007), S. marcescens was the causative pathogen in 8% of all bacterial nosocomial infections. S. marcescens has been identified as the responsible pathogen in 11% (Larson et al., 2005) and 16% (Graham et al., 2006) of all Gram-negative bloodstream infections (BSIs) in US-American NICUs. Since the organism is capable of surviving on the hands of healthcare workers (HCWs) (Milisavljevic et al., 2004) transient hand carriage is thought to foster nosocomial transmission.

In a case control study recently published by Al Jarousha et al. (Al Jarousha et al., 2008), S. marcescens was detected in blood cultures of 159 confirmed nosocomial BSIs. Seventy (44%) of these neonates died due to S. marcescens infection and 89 recovered. This study compared patients with S. marcescens sepsis with uninfected controls. Risk factors significantly associated with S. marcescens infection in multivariate analysis were birth weight <1,500 g (OR, 1.7; P=0.026); <37 weeks gestational age (OR, 2.0; P=0.002); and use of mechanical ventilation (OR, 2.3; P=0.001). The potentially devastating sequelae of late onset S. marcescens infections in preterm infants have been confirmed in a case series of Berger et al. (Berger et al., 2002) who reported five cases of septicemia with S. marcescens in neonates during a nosocomial outbreak (Assadian et al., 2002). Three of five patients developed meningitis with multiple brain abscesses. Mild clinical and laboratory findings of infection contrasted with excessive tissue destruction determined on MRI scans (Berger et al., 2002). Anderson et al. (Anderson et al., 2008) described a significantly higher infection rate in NICU patients colonized with S. marcescens (1:6; 17%) compared with infants colonized with Enterobacter cloacae (1:41; 2.4%), Enterobacter aerogenes (1:11; 9%), or Klebsiella pneumoniae (1:27; 3.7%).

The aim of this review is to describe important characteristics of S. marcescens outbreaks in neonatal and pediatric intensive care units. Hitherto, several nosocomial outbreaks of S. marcescens have been published, but no systematic analysis is available. The conclusions for clinical practice derived from this analysis are presented to support clinical decision making by the attending physicians, pediatric infectious disease specialists and hospital infection control teams in case of a S. marcescens outbreak in the NICU or PICU setting.

Section snippets

Materials and methods

The PUBMED database was utilized to search for publications with “Serratia marcescens” and “outbreak” as keywords, plus additional terms including “neonates”, “pediatric patients”, and “nosocomial infection”. In addition, the outbreak database, a web-based register for nosocomial outbreaks (http://www.outbreak-database.com/) was used to complete the literature search (Gastmeier et al., 2004). Citations were selected from articles published in English.

Studies were only included in the analysis

Basic data and infection rates (Table 1)

In total, 27 studies reporting on 34 outbreaks of S. marcescens were included in the analysis. The vast majority (93%) of reported outbreaks were from the NICU setting, one from a PICU (Cimolai et al., 1997), and one from a pediatric cardiac surgical intensive care unit (PCICU) (Manning et al., 2001); in two publications, the outbreak extended from the NICU to the PICU in the same hospital (Miranda et al., 1996; Steppberger et al., 2002). In total, 575 patients were involved.

Types of infection

The most prevalent

Conclusions

The different strategies of intervention to contain outbreaks of S. marcescens in the setting of neonatal or pediatric intensive care units have not been investigated in prospective randomized studies. Nonetheless, the available literature analyzed in this study demonstrates that nosocomial transmission of S. marcescens in outbreak settings can be successfully interrupted. From the perspective of the authors the points addressed in Table 4 should be considered by the outbreak management team.

Conflict of interest

None of the authors declares a conflict of interest.

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