Cyclosporiasis outbreak: What's this ‘explosive diarrhoea parasite’ on the rise in the US?

A nasty parasitic infection called Cyclosporiasis has sickened hundreds of people in Michigan and other parts of the United States.

On Thursday (July 2), the cases numbered more than 300, and the Michigan Department of Health and Human Services expects more cases as symptoms take a long time to appear, CBS News reported.

Cyclosporiasis, which causes "explosive" watery diarrhoea, has been on the rise in several states since May, according to the US Centres for Disease Control and Prevention (CDC). So far, at least 20 people have been admitted to hospitals across the country, but no deaths have been reported.

The culprit, Cyclosporiasis, is not deadly, and the source of the outbreak remains unclear.

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We take a look.

What is Cyclosporiasis?

It's a type of food poisoning. It can lead to diarrheal illness; however, it’s not usually life-threatening, according to the CDC. Infected individuals also start having low-grade fever, nausea, bloating and cramps one to two weeks after coming in contact.

Cyclospora cayetanensis is a microscopic parasite that’s found in human faeces. Cyclosporiasis outbreaks have been linked to various imported fresh produce, such as raspberries, basil, snow peas, mesclun lettuce, and cilantro, that were contaminated with the parasite, as per the CDC.

It's a seasonal illness in the US, with cases usually rising between May and August. Cyclosporiasis cases have been reported in many countries, including the US, but the infection is most common in tropical and subtropical regions.

How does Cyclosporiasis spread?

The disease cannot pass person-to-person through the air or by touching; however, it can spread through contact with human waste. One can be infected by ingesting tiny Cyclospora parasites through food or water contaminated with faeces.

The parasite usually takes 1 to 2 weeks outside the human body to become infectious, making person-to-person transmission highly unlikely, according to the CDC.

Vern Carruthers, University of Michigan microbiology and immunology professor, said, as quoted by CBS News, "You have someone or even a child who is in the pool; they'll release it into the water, and because it is so resistant to being killed by chlorine, people who are just ingesting that water have a chance of getting it (Cyclosporiasis)."

Cyclosporiasis cases in the US have been linked to fresh fruits and vegetables, including basil, cilantro, raspberries, and snow peas, Today reported.

Cyclosporiasis can be prevented by avoiding food or water that may be contaminated with faeces. Consistent hand hygiene and safe food-handling practices can also reduce the risk of foodborne illness.

What are Cyclosporiasis' symptoms?

Cyclosporiasis' main symptom is severe, watery “explosive” diarrhoea. Infected individuals also experience appetite loss, constant stomach cramps, nausea, vomiting and mild fever, the Cleveland Clinic reported.

Cyclosporiasis can last anywhere from a few days to over a month. Its symptoms often occur in waves and may return more than once after going away, a phenomenon known as a "relapse."

The infection is usually treated with a combination of antibiotics, although most people with strong immune systems recover without treatment. People with weak immune systems may face a higher risk of prolonged illness and symptom recurrence.

How are Cyclosporiasis cases on the rise in the US?

Clusters of cyclosporiasis cases are reported between May 1, 2026 and June 16 in 17 US states, Today reported, citing CDC data. New York has also reported the highest number of cases, as have Texas and Illinois.

The infected individuals range in age from 5 to 86. At least 20 have been hospitalised, though no deaths have been reported so far.

Across seven counties in Michigan, including Monroe, Lenawee, Washtenaw, Wayne, Livingston, Shiawassee, and Jackson, more than 170 cases have been reported since last week.

The CDC is working with the US Food and Drug Administration and state and local health officials to probe clusters of cases reported across several states.

The agency said all those infected fell ill after consuming food in the US, and none had travelled internationally in the weeks before becoming sick.

"There is no evidence of a single, multi-state Cyclospora outbreak linking all cases,” the CDC said on Wednesday (July 1), the report noted. An investigation is underway.

The US typically sees hundreds of cyclosporiasis cases annually. In recent years, the number of infections reported in the country has risen significantly.

With inputs from agencies