What to know about 'explosive diarrhoea' parasite outbreak in US

An outbreak of a diarrhoea-causing parasite is hitting more than half US states, with thousands of cases reported in recent weeks.

Cyclosporiasis is an infection caused by a microscopic parasite, with the main symptom being frequent, watery and explosive diarrhoea. People can become infected by consuming food or water that contains the parasite.

The outbreak now spans 31 states. It has hit Michigan particularly hard, with the state reporting on Friday that more than 1,000 people were diagnosed in a two-week period.

No deaths from the recent infections have been reported in the US. While the source has not yet been identified, past outbreaks have been linked to foodborne illness in raw produce.

Between 1 May and 9 July there were 843 confirmed cases of cyclosporiasis in the US, according to data released on Thursday by the US Centers for Disease Control and Prevention (CDC).

There are possibly hundreds more, with the public health agency saying on Friday it was aware of more than 1,500 cases that require further analysis to confirm the illness.

No deaths have been reported, and 86 people were admitted to hospital, the CDC said.

After Michigan, New York has seen the highest number of cases so far.Nearly 300 cases were reported there, state health officials said on 8 July.

In Illinois, public health officials reported 141 cases on 7 July, calling it a "higher-than-average" figure, and 177 cases of cyclosporiasis have been reported in Ohio, according to officials there.

The number of people sick with cyclosporiasis is likely higher than the number reported because some people recover without medical care and are not tested for the illness.

The CDC said it anticipates the case counts will continue to rise as new data comes in.

Cyclosporiasis is an intestinal illness caused by a microscopic parasite, according to the CDC.

People can become infected by consuming food or water that contains the parasite.

The illness is not usually life threatening, according to the CDC, and is less common than other foodborne illnesses such as salmonella and E. coli.

People who are infected with cyclospora may or may not experience symptoms. The illness usually causes diarrhoea "with frequent and sometimes explosive bowel movements", says the public health agency.

If untreated, the illness may last from a few days to over a month, and symptoms may return after appearing to dissipate.

It usually takes about one week after infection to become sick.

Person-to-person transmission does not occur, according to Dr Caitlin Rivers, of the Johns Hopkins Center for Health Security.

The epidemiologist wrote in an 8 July newsletter that transmission was exclusively faecal-oral via ingestion of contaminated food or water.

Those who were infected "became sick after eating food in the United States", the CDC said, and did not report any travel during the 14 days before they got sick.

No specific type of produce or any grower or supplier has been identified as the source.

"Contamination typically occurs at the farm or irrigation level, making traceback investigations difficult," Rivers wrote.

Previous cyclospora outbreaks in the US and Canada have been linked to bagged salad mixes and kits, fresh cilantro, fresh basil, raspberries, snow peas and green onions.

Given the large and increasing number of cases, Michigan's health department has recommended restaurants and kitchens preparing or serving raw produce reduce risk by thoroughly washing greens, cooking raspberries and leafy greens when possible, and removing outer layers of lettuce and green onions.

While the US Food and Drug Administration says rinsing produce is unlikely to be effective, the CDC still recommends it.

People who are experiencing diarrhoea are urged to contact a health provider and ask about possible infection, officials said.