A mysterious foodborne parasite outbreak has affected at least 145 people across 17 US states, while a separate surge in southeastern Michigan has sickened more than 150 people, health officials said. Investigators from the US Centres for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) believe contaminated food consumed within the country could be behind the infections, but the exact source has not yet been identified.

The illness is linked to Cyclospora cayetanensis, a microscopic parasite that causes cyclosporiasis, a stomach infection that can lead to prolonged diarrhoea and other digestive problems.

CDC surveillance data shows twenty patients have needed hospital treatment, but no deaths have been reported. Health officials said the outbreak is unusual because none of the infected people reported travelling outside the country before falling sick.

Cyclospora infections in the US are often connected to international travel, but investigators now suspect a food product sold domestically may have caused the current outbreak.

Cyclospora cayetanensis is a tiny parasite that affects the small intestine and causes an infection called cyclosporiasis. People usually become infected by eating food or drinking water contaminated with human faeces. Unlike some infections, health experts say there is currently no evidence that Cyclospora spreads directly from person to person.

Previous outbreaks in the US have often been linked to contaminated fresh produce, including leafy vegetables, herbs and berries, especially during warmer months.

Symptoms usually appear around one week after infection. Without treatment, the illness can continue for weeks or even months.

Common symptoms include:

• Watery diarrhoea
• Loss of appetite
• Weight loss
• Stomach cramps
• Bloating
• Increased gas
• Nausea
• Fatigue

Some people may also experience:

• Vomiting
• Mild fever
• Headache
• Body aches
• Flu-like symptoms

Doctors usually treat cyclosporiasis with antibiotics. In some cases, symptoms may improve temporarily but return later if treatment is not given.

Health authorities have advised people to follow basic food safety steps to reduce the risk of infection:

• Wash fruits and vegetables properly under clean running water.
• Use a clean brush to scrub firm produce such as cucumbers and melons.
• Cut away damaged or bruised sections before eating.
• Refrigerate peeled, cut or cooked fruits and vegetables within two hours.
• Avoid food or water that may have been contaminated.
• Seek medical advice if diarrhoea continues or stomach symptoms become severe.

Michigan officials have also advised people suffering from diarrhoea or vomiting to drink enough fluids, especially during hot weather.

New York has reported the highest number of infections, with 31 to 80 confirmed cases. Illinois and Texas have recorded between 11 and 30 cases each. Other states reporting infections include Alaska, Colorado, Connecticut, Florida, Georgia, Louisiana, Massachusetts, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia and Wisconsin. Each of these states has reported between one and 10 cases.

Officials warned that the number of infections could rise as investigations continue and more cases are identified.

While federal agencies investigate the nationwide cases, southeastern Michigan is facing its own growing outbreak. The Michigan Department of Health and Human Services (MDHHS) said the first case was detected on June 22. Since then, infections have been reported across Monroe, Lenawee, Washtenaw, Wayne, Livingston, Shiawassee and Jackson counties.

More than 150 people have fallen ill, making it one of Michigan’s largest recent Cyclospora outbreaks.

Monroe County has reported dozens of infections, with some patients requiring hospitalisation. Officials are interviewing affected people and reviewing their food histories to find a possible common source.

Investigators have not yet found the food item responsible for either outbreak. The CDC said, “Local, state and federal (CDC, FDA) public health authorities are investigating several clusters of cases in more than one state. Investigations to identify potential sources are ongoing.”

Michigan health officials also said they are continuing their investigation.