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.
What is cyclosporiasis?
The gastrointestinal illness is caused by the parasite cyclospora, which spreads through raw produce and water that has been contaminated with human feces.
In the US, it is a seasonal illness, with outbreaks tending to occur most often during the summer months between May and August. Past outbreaks have been linked to contaminated raw fruit, vegetables and herbs such as basil, cilantro, berries and spinach.
The most commonly reported symptom is watery diarrhea “with frequent and sometimes explosive bowel movements”, according to the CDC. Often the diarrhea may resolve and then return.
Other symptoms include cramps, nausea, fatigue, loss of appetite, low-grade fever and vomiting. Symptoms can last anywhere from several days to over a month. Some people do not have symptoms.
The average time from ingestion to symptoms is about a week, but can range from two days to about two weeks, the CDC says, and it is not usually transmitted from person to person.
Cyclosporiasis is not usually life-threatening and most people recover on their own. Those with weakened immune systems are more at risk. It is typically treated with antibiotics.
How does this compare to previous US outbreaks?
In the past, people in the US have been infected by consuming fruits or vegetables that were exposed to feces-contaminated irrigation water.
In 2022, a surge of cases in Florida was caused by contaminated lettuce in packaged salad kits that sickened hundreds of people.
While comprehensive data on cyclospora outbreaks is lacking, available information shows only a handful of documented outbreaks in the last 20 years have surpassed 1,000 cases, including a 1996 outbreak tied to Guatemalan raspberries that sickened almost 1,500 people, and a 2019 outbreak linked to Mexican basil that sickened more than 2,400 across the US and Canada.
How can you protect yourself from cyclosporiasis?
The best way to prevent infection with a parasite is to avoid food or water that may have been contaminated.
Fresh produce should be thoroughly washed before being eaten. Even so, cyclospora can cling to some foods, so washing may not eliminate the risk of infection entirely. Fruits, herbs and vegetables that have nooks and crannies – such as raspberries, blackberries, lettuce, spinach, cilantro, green onions, and basil – are more likely to harbor the parasite and can cause illness.
As health officials investigate the potential source, they recommend consumers purchase whole heads of lettuce rather than pre-washed, bagged lettuce or salad mixes, and remove the outer two to three leaves before washing the remaining ones under running water.
They also recommend cooking produce and vegetables when possible, which can kill the pathogen.
