Investigation of an outbreak of Stenotrophomonas maltophilia bacteraemia in an haemato-oncology unit: unexpected genetic diversity of isolates

Abstract number: R2437

Nahimana Tessemo I., Senn L., Bellini C., Blanc D.S., Zanetti G.

Introduction:Stenotrophomonas maltophilia (Sm) is ubiquitous in aqueous environment. Several nosocomial outbreaks have been reported, of which only 2 in haemato-oncology (HO) units. Between 1998 and 2006, 36 Sm bacteraemia occurred in our hospital (median 3/year, range 0–7) of which 14 in the HO unit (median 1.5/year, range 0–3). During a 5-week period (12.06–01.07), 3 new cases were diagnosed in the HO unit. An investigation was conducted to search a possible cross-transmission and a potential source.

Methods: Clinical and epidemiological data of the 3 patients with Sm bacteraemia were recorded. Environmental sampling of their rooms and of a fourth room of the same unit was done twice one month apart (02.07–03.07). One liter of water and swabs were taken from showers and faucets in each room (total 16 samples). For the 2nd sampling, swabs of sink siphons were also analysed. Isolates were identified to the species level by VITEK® 2 (bioMérieux, France) GN card. All Sm isolates were typed by pulsed-field gel electrophoresis (PFGE) using XbaI enzyme.

Results: The 3 patients were profoundly neutropenic at the time of Sm bacteraemia. All had received myeloablative chemotherapy. The 3 Sm isolates had 3 distinct PFGE patterns. One patient presented a second Sm bacteraemia 3 months later with a strain genetically identical to the first episode, suggesting a relapse. The first environmental investigation revealed that 3/16 samples yielded Sm. These 3 samples originated from 2 rooms, of which only one had been occupied by a patient with Sm bacteraemia. The second investigation revealed that the 4 siphons were contaminated with Sm. PFGE genotyping showed that each environmental isolate was unique. Moreover, no environmental isolate shared the same genotype with one of the clinical isolates. Of interest, Sm isolates recovered in 02.07 and 03.07 were different. No intervention was done, and so far (11.07) no new case occurred in the HO unit.

Conclusion: Molecular typing proved that there was no cross-transmission of Sm among patients. Environmental isolates were all different from clinical isolates, suggesting that the source of infection was not the water supply. However, as the isolates recovered during the first and the second investigations were genetically different, one can postulate that the environmental Sm flora is changing rapidly.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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