In which cases of pneumonia should we consider treatments for Stenotrophomonas maltophilia?

BACKGROUND: Stenotrophomonas maltophilia is a pathogen commonly associated with respiratory infection. However, the characteristics of pneumonia caused by S. maltophilia remain unknown. AIM: To evaluate the characteristics of and risk factors for S. maltophilia pneumonia. METHODS: A retrospective evaluation was undertaken of 2002 patients with sputum cultures positive for S. maltophilia between January 2010 and December 2019. Cases were excluded based on clinical information and laboratory results. Included cases were divided into two groups: the S. maltophilia pneumonia group (patients with pneumonia caused by S. maltophilia) and the non-S. maltophilia pneumonia group (patients with pneumonia caused by pathogens other than S. maltophilia). Patient characteristics, clinical data and Sequential Organ Failure Assessment (SOFA) scores were compared between the groups. FINDINGS: Eight and 91 patients were assigned to the S. maltophilia pneumonia and non-S. maltophilia pneumonia groups, respectively. The median age was significantly lower in the S. maltophilia pneumonia group than in the non-S. maltophilia pneumonia group (63.4 vs 73.1 years; P<0.01), and the SOFA score was significantly higher in the S. maltophilia pneumonia group (7.5 vs 3.0; P<0.01). Underlying malignancy and pre-administration of antipseudomonal ß-lactams and steroids were confirmed in seven of the eight cases in the S. maltophilia pneumonia group, suggesting an association with immunosuppression. CONCLUSIONS: Pneumonia due to S. maltophilia is a rare occurrence. Treatment for this pathogen should be considered in cases of pneumonia with: (1) predominance of S. maltophilia in sputum cultures; (2) pre-administration of broad-spectrum antibiotics; (3) immunodeficiency; and (4) a high SOFA score.