On October 22, 2018, the Vermont Department of Health told CDC's Waterborne Disease Prevention Branch about an outbreak of diarrhea caused by Shigella sonnei among residents, visitors and staff of a retirement community in Chittenden County, Vermont's most populous county.
Why it stood out
- High-quality single nucleotide polymorphism (SNP) analysis showed the first isolates were likely multidrug-resistant (MDR) and closely related — 0 to 11 SNPs apart — to a multistate cluster circulating at the same time.
- MDR shigellosis is rising in the United States. Outbreaks are more common among men who have sex with men, and rare in retirement communities.
CDC and the state worked together to find more cases, work out how the infection spread, and recommend control measures.
The cases
- Confirmed: S. sonnei grown from the stool of a resident, visitor or staff member, October 1–November 8.
- Probable: diarrheal illness in the same group and period, without a positive culture.
In all, 75 cases — 24 confirmed and 51 probable — fell ill between October 9 and November 3.
Shigellosis cases by date of illness onset (70 cases; five with unknown onset dates are not shown). Image from the Centers for Disease Control and Prevention
Tracing the source
Facility records and interviews found early cases in one staff member who prepared food while ill on October 11–14, and in six visitors who ate at the facility on October 14 — pointing to food.
A case-control study of 36 ill people and 172 well residents and staff compared what they had eaten and other shigellosis risks. Illness was linked to several facility meals on October 11–14, most strongly:
| Exposure | Odds ratio (95% CI) |
|---|---|
| Dining at the facility on October 14 | 5.6 (2.4–14.1) |
| Brunch that day | 5.5 (2.3–13.3) |
| Breakfast that day | 5.3 (1.2–22.9) |
Illness was not linked to large gatherings; no patient reported recent sexual contact or recreational water use; and interviews found no direct link to the multistate cluster.
Lessons
- Food handling was a key route of spread in the facility.
- Staff working while sick shows the value of clear, nonpunitive sick-leave policies.
- MDR shigellosis can reach many kinds of communities, so prevention strategies are needed for all vulnerable groups.
Sources
Based on "Notes from the Field: Outbreak of Multidrug-Resistant Shigella sonnei Infections in a Retirement Community — Vermont, October–November 2018," by Jonathan Strysko, Veronica Fialkowski, Zachary Marsh and colleagues, Morbidity and Mortality Weekly Report 68(17), Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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