Cilantro From Mexico Behind an Alabama Cyclosporiasis Outbreak, 2023

Cyclosporiasis is an intestinal illness caused by the parasite Cyclospora cayetanensis. It commonly brings diarrhea, abdominal cramps, nausea and loss of appetite. Most cases clear up on their own, but antibiotics can prevent relapses. In the United States, outbreaks are usually tied to fresh, imported produce.

The outbreak

In early June 2023, the Alabama Department of Public Health (ADPH) noticed five laboratory-confirmed cases, all in people who had eaten at the same Mexican-style restaurant in Limestone County and fallen ill May 26–30. It opened an investigation on June 7.

Cases by date of illness onset. Image from CDC's report

Interviews and outreach — including through the restaurant's food delivery contact list — found 42 more cases, for 47 in all:

Finding the food

A case-control study compared ill patrons with patrons who stayed well:

1. Of the menu items, only salsa roja was significantly linked to illness.
2. Of the fresh ingredients, four were: cilantro, jalapeños, onions and tomatoes.
3. In the final model, only cilantro stayed significantly linked (odds ratio 40.9).

Genotyping backed this up: of 29 specimens CDC could genotype, 23 (79%) shared one genetic cluster code, suggesting a common source.

The restaurant inspection on June 9 found nothing substantial, and the ingredients served during the outbreak had already been thrown away, so none could be tested — suggesting the produce arrived contaminated.

Tracing it back

The restaurant's invoices showed its produce came from a Georgia distributor. From July 10, the Georgia Department of Agriculture's Rapid Response Team led the traceback, working with counterparts in Florida, Pennsylvania and Texas:

How the suspected ingredients reached the restaurant. Image from CDC's report

Investigators found that a firm in the cilantro's supply chain had no identifiable food manufacturing license. The records couldn't show where in Mexico the cilantro was grown, and because states can't investigate across international borders, ADPH couldn't tell whether it was contaminated before or after harvest.

The response

• June 14: a statewide health alert to Alabama providers; June 15: a news release urging people to wash fresh produce well before eating, cutting or cooking.
• The restaurant was advised to switch produce suppliers — avoiding a closure — and to clean utensils and tools with high heat, because C. cayetanensis resists routine chemical disinfectants but is killed by heat.

Cilantro from Mexico has been identified as the source of cyclosporiasis infections repeatedly over the past three decades.

Lessons

The U.S. food supply is global and interconnected, so fast collaboration among health and agriculture agencies is essential to trace outbreaks. The authors call for active surveillance, regulatory oversight of food distributors — including checking business licenses — and education for distributors and restaurants, so contaminated produce doesn't move through improper supply channels.

Limits: the study was small (47 cases to 17 controls), so its estimates are imprecise; stepwise regression can be biased; and the cilantro itself could never be tested.

Sources

Based on Justine Goetzman, Adyneshia Carter, Ana Oliveira and L. Amanda Ingram (Alabama Department of Public Health), "Outbreak of Cyclosporiasis Among Patrons of a Mexican-Style Restaurant — Limestone County, Alabama, May–June 2023," MMWR, volume 74, Centers for Disease Control and Prevention; a work of the United States government in the public domain; rewritten in hubnx's own words. The report says both that the Texas firm and that a Georgia distributor lacked an identifiable food manufacturing license, so the firm is not named here.