A diarrhoea-causing parasite has infected people in 31 US states already, with multiple places reporting an uptick in the resulting illness in the last two weeks compared with a year ago, according to the US Centers for Disease Control and Prevention (CDC).

Here is what to know about the situation.

What is Cyclospora?

Cyclospora is a microscopic parasite that causes Cyclosporiasis, a severe gastrointestinal illness. It is transmitted through contaminated food and water. Health officials have not identified a specific source for the current US outbreak yet.

Where has it been found?

The Midwest has been the epicentre of the outbreak. Michigan has reported the highest number of infections with 1,562 cases in the state as at July 10, the health department said. Other states, including New York, Illinois and Ohio, have reported a major spike in cases. Case counts tend to rise in the spring and summer, according to the CDC.

As at July 10, CDC has registered more than 800 confirmed cases since May 1. There are more than 1,500 cases that the agency is still analysing. These figures are underestimates as the CDC data lags behind state health departments.

What are the symptoms?

The symptoms entail watery diarrhoea, loss of appetite and weight loss, though people who are infected also may not experience symptoms. It usually takes about a week for symptoms to manifest.

An infection can be treated with common antibiotics including Bactrim or Septra. No vaccine for the disease is available.

How does it spread?

The disease is transmitted indirectly between humans. The parasite takes one or two weeks living on produce or in water before it becomes harmful to humans when ingested. An infected person then can pass on the pathogen by touching food with unclean hands.

Outbreaks in the US have been linked to various types of fresh produce, including basil, cilantro, lettuce and raspberries.

The CDC advises avoiding food or water that may contain faeces, especially in tropical or subtropical areas. Otherwise, people should wash fruits and vegetables thoroughly and cut away any damaged or bruised areas.

No deaths have been recorded from the outbreak so far.

What’s the source?

The CDC and the Food and Drug Administration are working to determine the source of the outbreak. The Michigan health department has recommended people stop eating bagged lettuce and to thoroughly wash basil, cilantro and raspberries as a precaution.

Some franchise locations of Taco Bell in south-eastern Michigan have stopped offering lettuce during the outbreak, Bloomberg previously reported. No link to Taco Bell has been established, and the company declined to comment.

Have cuts to the CDC impacted tracking?

The CDC stopped tracking Cyclosporiasis through its FoodNet surveillance system, along with five other foodborne illnesses, in 2025. FoodNet is the agency’s real-time tracker of food-related diseases intended to spot outbreaks quickly in collaboration with 10 state health departments.

Cyclosporiasis is still a notifiable disease from health departments – meaning they must report positive cases to the CDC. However, the lack of FoodNet data has limited how much the US is able to track the ongoing outbreak in real time. BLOOMBERG