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

Cases of cyclosporiasis – a parasitic illness that can cause “explosive”, watery diarrhea – have surged across the United States in recent days, health officials have said, with an abnormally large outbreak of almost 1,000 cases reported in Michigan.

Michigan typically reports about 50 cases a year, making the current outbreak the largest in the state’s history and one of the nation’s biggest in recent years. Ohio has also reported a sharp increase, with 177 cases as of 2 July, since the CDC’s last count.

The US Centers for Disease Control and Prevention has recorded 145 cases across 17 states, as of 16 June, with some hospitalizations, but the agency’s data lags significantly behind state reporting and is likely a substantial undercount.

Although cyclosporiasis is rarely life-threatening, and no deaths have been linked to the current outbreak, the source of the infections has not yet been identified and illness can have severe effects. Here’s what you need to know.