The Centers for Disease Control and Prevention reported a disproportionately high incidence of group A Streptococcus infections among persons experiencing homelessness in Missoula County, Montana.
The findings highlight areas for improving early case detection to prevent severe disease, according to the agency. The incidence of invasive group A Streptococcus infections among persons experiencing homelessness is approximately 100 times that among persons in the general population, the report said.
Between July 2024 and September 2025, a total of 69 cases of the bacterial infection were identified in Missoula using routine and enhanced disease surveillance. Of the total infections, 39 cases occurred among 36 persons experiencing homelessness, while 30 cases were found among persons not experiencing homelessness. Montana made invasive cases a reportable condition in July 2024 because of the potential for the bacteria to cause severe disease.
The CDC reported that 34 of the 39 cases among persons experiencing homelessness required hospitalization. Fifteen were classified as invasive infections, defined as a positive culture from a normally sterile body site, streptococcal toxic shock syndrome, or necrotizing soft tissue infection, and one resulted in death. The report estimated the incidence of the infection among persons experiencing homelessness at 2,285.2 per 100,000 person-years, compared to 21.5 per 100,000 person-years for the county’s general population.
The Montana Department of Public Health and Human Services requested epidemiologic assistance from the CDC after routine monitoring initially linked 20 cases to two homeless shelters. By initiating enhanced surveillance, which included abstracting housing data from medical records and obtaining direct laboratory reports, investigators found 18 additional cases among persons experiencing homelessness.
At the time of diagnosis, wounds or skin breakdown were present in 34 of the 39 cases among persons experiencing homelessness. A history of substance use was documented in 27 of the 39 cases, with injection drug use noted in 10 patient encounters. Whole-genome sequencing of 23 bacterial isolates revealed six M protein gene types, which the CDC said suggests genetic diversity among infections and multiple transmission chains.
The Montana health department now routinely collects housing status data during invasive group A Streptococcus investigations to improve early disease detection and facilitate prompt public health action to prevent further spread, the report said.