The goal of this multicentre observational study is to analyse the treatment strategies and the outcomes for patients with S. maltophilia infections using target trial emulation methodology. The main question it aims to answer is:

• Does combined therapy achieve better results than monotherapy in treating S. maltophilia infections?

Researchers will compare groups receiving monotherapy and combined therapy to see if there are differences in all-cause 30-day mortality.

Inclusion Criteria:

• Adult patients
• S. maltophilia infections
• Different episodes if a new infection ocurred > 30 days since the index episode

Exclusion Criteria:

• isolates obtained from patients outside of hospital admission
• microbiological or clinical colonization
• hospitalizations shorter than 72 hours since the time zero
• patients who died in the first 72 hours since the time zero or who were in imminent risk of death
• polymicrobial infections
• receipt of inappropriate therapy after the time of the emulated randomization, defined as the absence of in vitro active antimicrobials or the administration of active antimicrobials for less than 48 hours
• absence of data outcomes

The selection criterion was the isolation of S. maltophilia in consecutive clinical samples from hospitalised adult patients, identified in microbiology laboratories between 2024 and 2025. The investigators first estimated the incidence of the S. maltophilia isolations per 1,000 admissions. Then, differenced episodes of infection defined if the treating physician considered of clinical significance the S. maltophilia isolation. Different infection episodes were considered from 30 days after the index episode.