Epidemiological investigation of a Serratia liquefaciens outbreak in a neurosurgery department

Between February 2001 and March 2003, 17 patients from the neurosurgery department of the University Hospital of Rangueil (Toulouse, Southern France) developed Serratia liquefaciens infections. Due to the atypical antibiotype displayed by the clinical isolates (i.e. gentamicin resistance), an outbreak was suspected. Molecular analysis carried out by pulsed-field gel electrophoresis demonstrated a genetic link for all patients. Furthermore, the patient who introduced the epidemic Serratia strain was also identified and shown to be related to the two epidemic peaks observed during the outbreak period. Investigation failed to reveal a reservoir among the antiseptics and soaps, or among the mechanical ventilators used. However, when the colonization of patients was investigated, positive carriage was observed and could be considered as a potential risk for the spread of the epidemic strain. Due to the delay between antibiotherapy and S. liquefaciens colonization, a selection effect had to be considered. Finally, implementation of hygiene measures was accompanied by control of the outbreak.