Severe strep A struck homeless people in Missoula at 106 times the general rate, CDC says

People experiencing homelessness in Missoula County, Montana, developed group A strep infections at 106.1 times the rate seen in the rest of the county’s population, according to a report published October 29, 2026, in the CDC’s Morbidity and Mortality Weekly Report. Investigators counted 69 cases between July 27, 2024, and September 20, 2025, and 39 of them were in people without housing. The homeless rate came to 2,285.2 cases per 100,000 person-years, against 21.5 for everyone else.

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Counting 69 cases over 1.15 years

Montana made invasive group A strep reportable on July 27, 2024. Routine surveillance from November 2024 through August 2025 turned up 20 cases epidemiologically linked to two Missoula homeless shelters, which led the state health department to ask CDC for an Epi-Aid. Enhanced surveillance began in September 2025 and reached back to the reportable date, pulling laboratory reports and medical records directly from facilities and sequencing bacterial genomes at the Utah Public Health Laboratory and CDC.

The MMWR report (DOI 10.15585/mmwr.mm7542a1), led by Beth Hopkins of Montana’s health department, found that the 39 cases among homeless residents involved 36 people, because three were infected twice. Eighteen of the 39 (46%) came to light only through the enhanced work. The rate ratio of 106.1 carries a 95% confidence interval of 65.9 to 170.7, and it rests on a denominator of 1,484 homeless residents taken from a 2024 community estimate, against 121,062 other residents from a Census projection.

A CDC conference abstract on the same investigation adds that it began in February 2025, when Montana’s health department identified multiple severe cases, and that among homeless cases 85 percent were male, 62 percent were White and 26 percent were American Indian. It put the share presenting with wounds and active infection at 74 percent, a figure that differs from the 87 percent in the published report, presumably because of case definitions or the abstract’s earlier data cut.

Hospitalizations, wounds and one death

Severity was high. Of the 39 cases among homeless residents, 34 (87%) required hospitalization, 15 (38%) were invasive disease, and one invasive patient died. Among the 30 cases in housed residents, 18 (60%) were hospitalized and 9 (50%) were invasive. All three people who were reinfected had invasive disease both times.

Skin was the common thread in the clinical picture. Wounds or skin breakdown were present at diagnosis in 34 (87%) of the homeless cases, 27 (69%) had a history of substance use, and injection drug use was documented in 10 encounters (26%). CDC’s group A strep overview lists wounds and skin disease among the factors that raise the risk of serious infection, along with injecting drugs and experiencing homelessness, and notes that bacteria can spread through contact with infected sores.

Six emm types and the multiple transmission chains

Sequencing of 23 isolates showed six emm types, the gene-based labels used to sort strains of the bacterium, and no single type accounted for even half of the cases that were sequenced. Ten were emm 58.2 and nine were emm 49, with single isolates of emm 53, 76, 85 and 92 making up the rest. That spread suggests many separate introductions rather than one outbreak strain, a reading echoed in a CDC conference abstract on the investigation, which said whole-genome sequencing pointed to multiple unrelated transmission events and that a high prevalence of wounds argued for wound prevention, better access to care and targeted health messaging.

The Missoula numbers fit a national picture. CDC’s invasive strep surveillance page estimates 20,000 to 27,000 invasive cases and 1,800 to 2,400 deaths a year, and says people experiencing homelessness and people who inject drugs account for much of the rise in adult cases.

For clinicians and shelter staff the message in the data is about skin. Wound care, access to treatment and early flagging of housing status are the levers the authors point to, because the bacteria move through breaks in the skin and close contact. The report recommends capturing housing status to improve case classification and calls early detection in this population a high priority for preventing severe disease.

Limits of the estimate and what Montana changed

Hopkins and her coauthors say the true incidence among homeless residents is likely higher than 106.1 suggests, because of barriers to health care, differences in how cases are found by housing status, a shifting population count and incomplete housing classification. They write that the burden was “missed by routine surveillance activities,” a gap the enhanced effort closed.

The comparison also has a built-in conservatism that is easy to overlook. Because the general-population denominator in the report excludes the 1,484 homeless residents, the 106.1 ratio compares two groups that do not overlap, and the 30 housed cases used for the baseline are themselves a count of illness that the same investigators located through the same laboratory and hospital records. That makes the gap more credible, not less, although the authors caution that housing status was incompletely recorded in medical charts.

Montana’s health department now records housing status routinely during invasive group A strep investigations and is exploring thresholds for when to scale enhanced surveillance up or down. The report does not say whether cases have continued after September 2025, so whether the shelter-linked cluster has ended remains an open question.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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