A diarrhoea-causing intestinal parasite known as Cyclospora is spreading across the United States, with at least 145 people infected and more than 20 hospitalised as health authorities work to identify the source of the outbreak. Cases have been recorded in people aged between five and 86, with data from the US Centres for Disease Control and Prevention covering the period from 1 May to 16 June 2026 .
No deaths have been reported, but officials warn the true number of infections is likely significantly higher than the confirmed case count, with unreleased data expected to paint a more alarming picture.
Which states are affected?
New York has recorded the highest number of infections, with between 31 and 80 confirmed cases — making it the hardest-hit state in the outbreak so far. A wide range of other states have also logged infections, including:
Meanwhile, health officials in Michigan are investigating what has been described as a "sudden and large" increase in cases within the state. It is understood Michigan has recorded more than 170 cases linked to the current outbreak — a dramatic spike compared to the roughly 50 cases the state typically sees in an entire year, according to a spokesperson for the Michigan Health Department.
How is Cyclospora transmitted and what are the symptoms?
Cyclospora is ordinarily contracted through consuming water or food contaminated by faeces. Notably, none of the people infected in this outbreak are believed to have travelled outside the United States recently, suggesting a domestic food source is the likely culprit — though health authorities have not yet identified a specific food item responsible.
Symptoms typically appear around one week after infection . The most common and distinctive symptom, according to the CDC, is "watery diarrhoea with frequent and sometimes explosive bowel movements." Other commonly reported symptoms include:
Less commonly, people have also experienced vomiting, body aches, headaches, fever and flu-like symptoms. The duration of illness can vary considerably, lasting anywhere from a few days to more than a month .
Is this outbreak unusual?
While the scale of the current outbreak has raised concern — particularly in Michigan — Cyclospora is not an uncommon illness in the United States. The country typically records several hundred cases per year , and the parasite is classified as a "nationally notifiable disease," meaning every confirmed case must be formally reported to government health authorities.
What makes this cluster notable is the concentration of cases in a short timeframe and the absence of any recent international travel among those infected — a common route of transmission. The sudden surge in Michigan, a state that ordinarily sees just 50 annual cases, has particularly drawn the attention of state-level health investigators.
What should people watch for?
Anyone experiencing persistent watery diarrhoea, unexplained fatigue, nausea or stomach cramping is advised to seek medical attention. As with other illness outbreaks that have led to hospitalisations, early medical assessment can be important in preventing complications, particularly for vulnerable age groups such as young children and the elderly — both of whom are represented among those infected in this outbreak.
Federal health authorities continue to investigate the source of contamination, and further updates are expected as the case count is reassessed against more recent data.
