Heterogeneous Serratia marcescens genotypes from a nosocomial pediatric outbreak

Objective: Define the applicability of a rapid molecular typing scheme to study the epidemiology of a Serratia marcescens outbreak. Design: With the assistance of a simple bacterial lysis technique, isolates of S marcescens from a putative outbreak were genotyped with the polymerase chain reaction technology for which primers were chosen on the basis of previously defined enterobacterial repetitive intergenic consensus sequences. Setting: Pediatric ICU. Patients: Intensively monitored patients who were found to yield S marcescens from any body site during the epidemic period. Results: Over an 8-month period, 12 ICU patients were either infected or colonized with S marcescens. All of these patients were transiently supported by artificial ventilation. During the epidemiologic investigation, a dilution error in a high-level glutaraldehyde disinfectant, which was being used for some ventilator components, was observed. Rectification of the error was associated with an abrupt termination of the outbreak, Enterobacterial repetitive intergenic consensus polymerase chain reaction was easily applicable to this setting and it defined 4 distinct genotypes among the 12 isolates. Conclusion: The typing method is easily implemented and offers great promise as an epidemiologic tool, The associated investigation served to emphasize that an outbreak may occur with more than one epidemic strain and that strain heterogeneity itself does not exclude an outbreak.