More than 27,000 confirmed and probable cases of cyclosporiasis have now been reported across 47 US states, as health officials continue investigating multiple outbreaks of the parasite-linked illness.

The latest figures from the Centers for Disease Control and Prevention show 15,716 laboratory-confirmed cases, along with another 11,841 suspected cases still under investigation, since May 1.

The outbreak has been particularly severe in Michigan, where 14,277 cases and 335 hospitalisations have been reported. Two people infected with cyclosporiasis have also died in the state.

Recalled lettuce linked to major outbreak

The Food and Drug Administration said this week that recalled iceberg lettuce from a Taylor Farms facility in central Mexico may have been distributed across nine additional states and jurisdictions.

The areas include California, Delaware, North Dakota, Rhode Island, South Dakota, Vermont, Washington, Washington DC and Puerto Rico.

The FDA previously said the recalled lettuce had been distributed to restaurants and retailers in nearly three dozen states between late June and July.

The agency said the lettuce-linked outbreak had accounted for 10,930 illnesses across 17 states in its latest investigation.

The recalled products should no longer be available for sale, and their best-by dates have already passed.

Taco Bell pulls lettuce

Some Michigan residents were reportedly infected after eating at Taco Bell restaurants. The fast-food chain subsequently removed lettuce from its outlets as a precaution.

However, health authorities are also investigating smaller clusters of cyclosporiasis whose sources remain unknown.

US health officials are working with state and local authorities to identify possible sources of exposure and provide information on how people can reduce their risk.

What is cyclosporiasis?

Cyclosporiasis is a gastrointestinal infection caused by the parasite Cyclospora cayetanensis. The parasite can spread when food or water becomes contaminated with human waste.

Fresh produce can become contaminated through polluted water used during cultivation or through handling by an infected person.

Previous outbreaks have been associated with foods including cilantro, raspberries, basil, snow peas and lettuce.

Symptoms can include prolonged or severe diarrhoea, vomiting, nausea, stomach discomfort and dehydration. While the infection is generally not life-threatening, some patients may require hospital treatment.

Symptoms can take around two weeks to appear after exposure, making it difficult for investigators to determine which food caused an infection.

How to reduce the risk

Cooking food thoroughly can help kill the parasite. Washing fresh produce carefully can also reduce the risk of exposure, although washing does not completely eliminate Cyclospora.

Consumers should also check food recall notices and avoid eating recalled produce.

The FDA and CDC continue to monitor the outbreak as officials work to identify additional sources of infection.