Pseudo-outbreaks of Stenotrophomonas maltophilia on an intensive care unit in England

SummaryBackgroundIn June 2014, a cluster of identical S. maltophilia isolates was reported in an adult intensive care unit (ICU) at a district general hospital. An outbreak control team was convened to investigate the cluster and inform control measures.AimTo identify potential risk factors for isolation of S. maltophilia in this setting.MethodsWe conducted a cohort study of ICU patients for whom a bronchoalveolar lavage (BAL) specimen was submitted between October 2013 and October 2014. Cases were patients with S. maltophilia-positive BAL. We calculated the association between isolation of S. maltophilia and patient characteristics using risk ratios (RRs) with 95% confidence intervals (95% CIs) and univariate logistic regression. Chi-squared or Fisher's exact tests were used. BAL specimens were microbiologically typed using pulse-field gel electrophoresis (PFGE).FindingsEighteen patients met the case definition. Two patients had clinical presentations that warranted antibiotic treatment for S. maltophilia. All cases were exposed to bronchoscopy. PFGE typing revealed clusters of two strain types. We found statistically significant elevated risks of isolating BRISPOSM-4 in patients exposed to bronchoscope A (RR: 13.56; 95% CI: 1.82–100; P < 0.001) and BRISPOSM-3 in patients exposed to bronchoscope B (RR: 16.89; 95% CI: 2.14–133; P < 0.001). S. maltophilia type BRISPOSM-4 was isolated in water used to flush bronchoscope A after decontamination.ConclusionTwo pseudo-outbreaks occurred in which BAL specimens had been contaminated by reusable bronchoscopes. We cannot exclude the potential for colonization of the lower respiratory tract of exposed patients. Introduction of single-use bronchoscopes was an effective control measure.