Cluster of S. maltophilia among patients with respiratory tract infections at an intensive care unit

BACKGROUND: Stenotrophomonas maltophilia is associated with respiratory tract infections in immunocompromised patients, and it has emerged as an important nosocomial pathogen, with admission to intensive care units (ICUs) and ventilators as recognized risk factors. AIM: To describe the investigation of a sudden increase in patients with pneumonia caused by S. maltophilia at a Swedish ICU and the control measures taken. METHODS: Lower respiratory tract cultures from patients admitted to the ICU were obtained, and environmental cultures were collected from sink drains and medical equipment. Isolates identified as S. maltophilia were subjected to antibiotic susceptibility testing and whole genome sequencing (WGS). FINDINGS: A total of 17 S. maltophilia isolates were found (four from patients and 13 from the environment). The WGS identified two outbreak clones, sequence type (ST) 361 and ST138, and seven unique ones. Most likely, the outbreak clones originated from two sinks, and transmission was enhanced by a calorimeter. After changing the sink and calorimeter routines, no more cases were registered. CONCLUSION: Acquisition of S. maltophilia from the hospital environment appears to be easy, especially if water is involved. To control this bacterium, better knowledge of its transmission routes in hospital environments is required.