Significance of positive Stenotrophomonas maltophilia culture in acute respiratory tract infection

Stenotrophomonas maltophilia is a common coloniser of the respiratory tract of patients with chronic lung disease, and, in the absence of pneumonia or bacteraemia, is often ignored by physicians at the Royal Perth Hospital (Perth, Australia). Experience at the Royal Perth Hospital was reviewed to determine whether ignoring S. maltophilia in this setting has any apparent effect on clinical outcome. All patients who presented with an acute respiratory illness and yielded a positive culture for S. maltophilia between 1995 and 2002 were retrospectively reviewed. All subjects had to yield a positive respiratory isolate of S. maltophilia and undergo chest radiography within 24 h of the isolate being obtained. Ninety-two episodes were identified in 89 individuals; 64 showed no evidence of consolidation. Of the study group, 51 (80.0%) received no anti-S. maltophilia antibiotic therapy and 21 (32.8%) had a nosocomially acquired isolate. The overall mortality rate was 20.3%. There was no impact of anti-S. maltophilia therapy on outcome. The only independent predictor of mortality was serum albumin level. As there was no measurable impact of antibiotic therapy, in the absence of consolidation, a positive respiratory tract isolate of Stenotrophomonas maltophilia probably represents colonisation of a severely impaired host rather than invasive disease.