Outbreak of Invasive Serratia marcescens among Persons Incarcerated in a State Prison, California, USA, March 2020–December 2022

S erratia marcescens, a gram-negative environmental bacterium (1,2), is an opportunistic pathogen that in rare cases causes invasive diseases, including bacteremia and endocarditis (1,3-7).Reported outbreaks have been linked to contaminated environmental sources, such as water, soap, intravenous fluids, and compounded drugs (8-16) in nosocomial settings (17-19).Invasive S. marcescens infections have occurred among persons who inject drugs (5,6,(20)(21)(22).Given the high prevalence of injection drug use (IDU) in prisons and lack of access to sterile needles (23-25), risks for transmission of bloodborne pathogens are higher than among the general population (25).Cell Block 64 (CB64) solution, produced by California Prison Industry (CALPIA, https://www.calpia.ca.gov), is a quaternary ammonium concentrate (https:// catalog.calpia.ca.gov/custom/assets/Files/view-current-sds-information-16.pdf)used as the primary disinfectant in prisons in California, USA.However, S. marcescens can survive in improperly prepared disinfection solutions, including quaternary ammonium disinfectants (18,19,26).We describe a multiyear outbreak of invasive S. marcescens infections driven by widespread environmental contamination, improperly prepared and maintained disinfection solution, IDU, and social connections at a California state prison.Prison A is a maximum-security state prison housing ≈3,000 male incarcerated persons.In October 2020, the primary hospital affiliated with prison A notified the California Correctional Health Care System (CCHCS) that multiple incarcerated persons had been admitted with invasive S. marcescens infections.CCHCS, Monterey County Public Health Laboratory (MCPHL), and California Department of Public Health (CDPH) began a multidisciplinary investigation to identify additional cases, determine risk factors for infection, and provide recommendations for mitigation and Outbreak of Invasive Serratia marcescens among Persons Incarcerated in a State Prison, California, USA,