Stenotrophomonas maltophilia ventilator-associated pneumonia. A retrospective matched case-control study

BACKGROUND: Stenotrophomonas maltophilia is increasingly identified in critically ill patients, but it is considered a pathogen with limited pathogenicity and it is therefore infrequently targeted. This study explores whether S. maltophilia may cause ventilator-associated pneumonia (VAP) and whether it affects intensive care unit (ICU) mortality and 28-day mortality when compared to VAP caused by other Gram-negative bacilli. METHODS: Retrospective analysis of a 19-year prospectively collected database. Stenotrophomonas maltophilia as a cause was considered in VAP-suspected cases when S. maltophilia growth of ≥10(4) cfu/ml was detected in bronchoalveolar lavage fluid analysis. Cases were matched on hospital, gender, age and acute physiology and chronic health evaluation II score in a 1:3 ratio with controls from the same database suffering from VAP caused by other Gram-negative bacilli. RESULTS: Eight cases met the inclusion criteria, of which three were labelled as 'probable' SM-VAP and three as 'possible' SM-VAP. These six patients constitute 1.8% of all VAPs in the studied period. No significant differences in baseline characteristics and duration of mechanical ventilation (p = 0.68), length of stay in the ICU (p = 0.55) and hospital (p = 0.84) between cases and controls were identified between cases and controls. Intensive care unit mortality odds ratio was 1.7 (p = 0.55; 95% CI 0.3-10.5) and 28-day mortality odds ratio was 1.4 (p = 0.70; 95% CI 0.2-9.1). CONCLUSIONS: Stenotrophomonas maltophilia is a possible, yet infrequent cause of VAP. No outcome differences were found when compared to matched VAP caused by other Gram-negative bacilli