Cyclospora outbreaks causing diarrhea in US expected to continue through August

Centers for Disease Control and Prevention says it is scouring food supply chain for culprit, which may be lettuce

What is cyclosporiasis, the parasitic illness causing ‘explosive’ diarrhea?

Federal health officials have said they expect the outbreaks of cyclospora – a parasite that causes watery, explosive diarrhea – across the US to continue through August as they scour the food supply chain for the culprit.

The Centers for Disease Control and Prevention (CDC) has identified 1,645 lab-confirmed cases of the parasite; reported that 145 people have been hospitalized; and reported that they have a backlog of 5,100 cases that require more analysis, including interviews.

“The true number of infections is almost certainly higher, because many people with mild illness recover,” said Gwen Biggerstaff, deputy director of the CDC’s division of foodborne, waterborne, and environmental diseases, said at a media briefing on Tuesday. “We’re seeing an unusually high number of cyclosporiasis cases this summer.”

Health officials said outbreaks in Michigan, Ohio, West Virginia and Kentucky are linked, though they could not yet identify the source of the outbreak. On Monday, officials in Michigan warned the public that lettuce was a “potential source” of the outbreak, but that the investigation continued. Federal and state officials are investigating whether lettuce at Taco Bell locations in Michigan may be linked to the outbreak, according to the Washington Post .

State officials have been reporting much higher numbers of people sickened during the outbreak than the CDC are, likely due to reporting delays. On Monday, officials in Michigan said more than 2,800 people had been sickened in the outbreak.

Cyclosporiasis is a parasitic infection caused by the single-cell protozoa cyclospora. The microbe is typically transmitted through water or food contaminated with feces. It is most common during warm weather months, from May to August.

The parasite is difficult to track because it has a long incubation period – a person may be infected anywhere from days to weeks before symptoms begin. Diagnosis and reporting takes weeks more. As a result, patients are often asked to recall what they ate six to eight weeks prior.

Past outbreaks have been linked to bagged salads, herbs, raspberries and lettuce. Experts believe prevalence of the condition may be increasing due to climate change , as more warm days allow the microbe to thrive. Federal and state officials have warned Americans to thoroughly wash fresh produce or, ideally, cook it.

“Cyclospora remains a challenging agent,” said Donald Prater, the FDA’s acting deputy commissioner for food. “Our outbreak investigation team is hard at work to follow all the leads we have from CDC for all the various outbreak clusters we have.”

The Trump administration has come under criticism from public health foodborne illness experts as the outbreak expands. In the year leading up to the outbreak, the Trump administration cut $11.4bn from state and local health departments, and significantly narrowed the scope of a CDC program that surveilled trends in foodborne illness called FoodNet.

Biggerstaff said the CDC is holding weekly phone calls with states about the outbreak, but did not say that the agency had deployed staff. She also acknowledged that state budgets are tight.

“States are often under-resourced for things like foodborne outbreak and response,” said Biggerstaff. “CDC is actively engaged.”

The CDC had warned for years leading up to the cuts that “[c]omprehensive efforts are needed to improve food safety”. The agency also warned that cyclospora infections were on the rise. In a study from 2022, research found a 443% increase in infections when comparing the period from 2016 to 2018, to 2021. Later communications from the agency said the increase may reflect “improved detection of infections rather than true increases in the number of cases”.

One of Biggerstaff’s messages to the public was to advocate for a cyclospora test if they are concerned they may have the parasite. Cyclosporiasis may not be included in typical stool panels, and sometimes require a special test.

“The gap in surveillance I would like to focus on is people who would not seek care, and if they do seek care they don’t get tested,” said Biggerstaff.