# Stenotrophomonas maltophilia Bloodstream Infection Outbreak in Acute Care Hospital, California, USA, 2022–2023

## TL;DR

A hospital in California traced an outbreak of Stenotrophomonas maltophilia bloodstream infections to possible contamination from nonsterile water.

## Contribution

The study identified specific risk factors and potential transmission routes for an S. maltophilia outbreak in a hospital setting.

## Key findings

- Exposure to iodinated contrast, propofol, or fentanyl was linked to increased odds of S. maltophilia infection.
- Whole-genome sequencing showed the isolates were highly related, indicating a common source.
- The outbreak was likely due to nonsterile water contamination, though no culture confirmation was obtained.

## Abstract

Stenotrophomonas maltophilia is an opportunistic bacterial pathogen found in healthcare settings. During May 2022–September 2023, an acute care hospital in northern California, USA, identified 13 S. maltophilia bloodstream infections among intensive care unit patients. Whole-genome sequencing showed the isolates were highly related. We identified risk factors for infection by conducting a matched case–control study, targeted assessment of infection prevention and control practices, and laboratory testing of suspected environmental reservoirs. Among 13 case-patients and 39 control-patients, patients exposed to iodinated contrast (odds ratio [OR] 12.0; 95% CI 2.1–∞), injectable propofol (OR 12.2; 95% CI 1.5–101.4), or fentanyl (OR 9.2; 95% CI 1.8–∞) had increased odds of S. maltophilia bloodstream infection. Although we did not have culture confirmation of a source, we suspect S. maltophilia was transmitted by exposure to nonsterile water from a common source. We recommended infection prevention and control practices to reduce risk for contamination from nonsterile water.