Objective: To describe the investigation of a pseudo-outbreak of multiresistant Pseudomonas aeruginosa fecal colonization in a hematology unit.
Design: Retrospective chart review; prospective environmental sampling and observation of stool culture technique; genotyping by random arbitrary primer polymorphic DNA polymerase chain reaction (RAPD-PCR).
Setting: An academic tertiary-care hospital.
Patients: Between August and October 1994, P aeruginosa resistant to imipenem, ceftazidime, ciprofloxacin, and all aminoglycosides was isolated from surveillance stool cultures from 10 neutropenic patients cared for in the hematology unit. P aeruginosa, with an identical susceptibility pattern, was isolated from three patients admitted to the same unit in the year before the "outbreak." Two months before the outbreak, 12 healthcare workers had been added to the staff.
Results: Observation of stool sampling techniques as performed by healthcare workers revealed that samples for surveillance cultures were taken from feces in the toilet. When the proper sampling technique was used, P aeruginosa was not isolated from stool samples from 8 of 10 patients with previously positive cultures. P aeruginosa also was isolated from two wash basins, toilet flushing water, and a toilet brush. Genotyping by RAPD-PCR showed that the isolate from the toilet flushing water was identical to the P aeruginosa strains of eight patients from the outbreak.
Conclusions: This pseudo-outbreak emphasizes the importance of proper sampling techniques and that periodic observation may be necessary to verify proper sampling techniques.