Health officials in the United States are reporting a significant increase in cases of cyclosporiasis, a parasitic infection known for causing severe gastrointestinal symptoms. Michigan, in particular, has seen an abnormally large outbreak, with almost 1,000 cases recorded – a stark contrast to its typical annual average of around 50 cases. This makes it the state's largest outbreak of the illness to date and one of the most substantial in the US in recent years. Ohio has also experienced a sharp rise, with 177 cases reported as of 2 July 2026.
The US Centers for Disease Control and Prevention (CDC) had recorded 145 cases across 17 states as of 16 June 2026, including some hospitalisations. However, the CDC acknowledges that its data often lags behind state reporting, suggesting the true number of infections is likely a significant undercount. While cyclosporiasis is generally not life-threatening, and no fatalities have been linked to the current surge, the illness can lead to severe and debilitating effects, including prolonged periods of 'explosive', watery diarrhoea.
Cyclosporiasis is caused by the microscopic parasite Cyclospora cayetanensis. People become infected by consuming food or water contaminated with the parasite. Historically, outbreaks have been associated with fresh produce such as berries, herbs, and leafy greens. The incubation period can range from a few days to several weeks, with symptoms typically appearing about a week after exposure. These symptoms often include sudden onset of watery diarrhoea, loss of appetite, weight loss, abdominal cramps, bloating, nausea, and fatigue.
For UK residents, while cyclosporiasis is not common, it is important to be aware, particularly when travelling internationally. The NHS advises that travellers to areas where food and water hygiene may be poor should take precautions, such as drinking bottled water and avoiding uncooked foods. In the UK, cases are usually sporadic and often linked to imported contaminated produce or individuals returning from affected regions. Public Health England (now the UK Health Security Agency) regularly monitors foodborne illnesses, and any unusual cluster of cases would prompt investigation.
Diagnosis of cyclosporiasis typically involves laboratory testing of stool samples. Treatment usually consists of a course of antibiotics. Without treatment, symptoms can persist for several weeks or even months, with periods of remission and relapse. NICE (National Institute for Health and Care Excellence) guidelines on managing diarrhoeal illnesses emphasise the importance of rehydration and, where appropriate, antimicrobial therapy based on identified pathogens. Good hand hygiene, especially after using the toilet and before handling food, is crucial in preventing the spread of the parasite.