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Three consecutive outbreaks of Serratia marcescens in a neonatal intensive care unit
Felix Fleisch1, Urs Zimmermann-Baer, Reinhard Zbinden
1Division of Infectious Diseases and Hospital Epidemiology, University Hospital of Zurich, CH-8091 Zurich, Switzerland.
Abstract:
We investigated an outbreak of Serratia marcescens in the neonatal intensive care unit (NICU) of the University Hospital of Zurich. S. marcescens infection was detected in 4 children transferred from the NICU to the University Children's Hospital (Zurich). All isolates showed identical banding patterns by pulsed-field gel electrophoresis (PFGE). In a prevalence survey, 11 of 20 neonates were found to be colonized. S. marcescens was isolated from bottles of liquid theophylline. Despite replacement of these bottles, S. marcescens colonization was detected in additional patients. Prospective collection of stool and gastric aspirate specimens revealed that colonization occurred in some babies within 24 hours after delivery. These isolates showed a different genotype. Cultures of milk from used milk bottles yielded S. marcescens. These isolates showed a third genotype. The method of reprocessing bottles was changed to thermal disinfection. In follow-up prevalence studies, 0 of 29 neonates were found to be colonized by S. marcescens. In summary, 3 consecutive outbreaks caused by 3 genetically unrelated clones of S. marcescens could be documented. Contaminated milk could be identified as the source of at least the third outbreak.
Insights
Three Serratia marcescens outbreaks occurred in a neonatal intensive care unit (NICU). Contaminated milk bottles were identified as the source of the third outbreak, leading to improved disinfection protocols and zero new infections.
Area of Science:
- Infectious Diseases
- Neonatology
- Microbiology
Background:
- Serratia marcescens (S. marcescens) outbreaks pose a significant risk in neonatal intensive care units (NICUs).
- Identifying the source and transmission routes of S. marcescens is crucial for effective infection control in vulnerable infant populations.
Purpose of the Study:
- To investigate and characterize three consecutive outbreaks of S. marcescens in a hospital NICU.
- To identify the sources of infection and implement control measures to prevent further transmission.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) was used to analyze the genetic relatedness of S. marcescens isolates.
- Prevalence surveys and specimen collection (stool, gastric aspirate, milk, bottle contents) were conducted.
- Bottle reprocessing methods were modified to thermal disinfection.
Main Results:
- Three genetically distinct S. marcescens clones were identified, causing consecutive outbreaks.
- S. marcescens was isolated from liquid theophylline bottles and milk in used milk bottles.
- Colonization was observed in neonates within 24 hours of delivery, with different genotypes.
- Following thermal disinfection of bottles, no further S. marcescens colonization was detected in 29 neonates.
Conclusions:
- Contaminated milk was identified as the source of the third S. marcescens outbreak.
- Implementing thermal disinfection for bottle reprocessing effectively controlled S. marcescens transmission in the NICU.
- Multi-clonal S. marcescens outbreaks can occur, necessitating rigorous source identification and control strategies.