Thousands Sickened By 'Explosive' Diarrhoea Across US: The Parasite Lurking In Salads

A fast-spreading outbreak of a microscopic parasite has sickened thousands of Americans this summer, triggering a nationwide health scare, emptying salad bars and putting food safety officials on high alert across more than 30 states.

What Is Happening

Health authorities in the United States are racing to trace the source of a large outbreak of cyclosporiasis, an intestinal illness caused by the parasite Cyclospora cayetanensis. According to the US Centers for Disease Control and Prevention (CDC), nearly 7,000 confirmed or probable cases have now been reported across at least 34 states, making it one of the largest outbreaks of foodborne illness in the US in years.

Of these, the CDC has confirmed 1,645 laboratory-confirmed cases since May 1, with more than 5,100 additional cases still under investigation, a number officials say is far higher than the 249 cases recorded nationally at the same point last year.

Michigan and Ohio at the Centre of the Storm

The outbreak's epicentre appears to be the American Midwest. More than 3,000 cases have now been recorded in Michigan and Ohio alone, and investigators believe lettuce or salad greens may be the source. Michigan alone has reported over 3,300 cases, according to CDC data cited by NBC News.

Michigan's chief medical executive, Dr Natasha Bagdasarian, said early findings kept pointing investigators toward one culprit, though she cautioned that other foods cannot yet be ruled out, and no specific product, grower or supplier has been officially identified.

In a significant development, the CDC has now linked cases across four Midwestern states, Michigan, Ohio, West Virginia and Kentucky, as part of a single, connected outbreak of roughly 400 illnesses, according to reporting by The Washington Post, which noted authorities are also examining a possible connection to Taco Bell restaurants.

What the Parasite Does to the Body

Cyclospora spreads when people consume food or water contaminated with human faecal matter, often through tainted irrigation water, poor farm labour conditions, or runoff into fields where produce is grown, per the CDC's explanation cited by CNN.

Symptoms typically begin one to two weeks after exposure, starting with fatigue and body aches before progressing to the illness's signature symptom: sudden, watery, and frequently "explosive" diarrhoea, along with bloating, cramping and nausea, NBC News and TODAY.com reported. Unlike a typical stomach bug, the illness can drag on for weeks if untreated and is usually managed with the antibiotic Bactrim.

One Michigan Reddit user, whose account was cited by CNN, described being left "weak, fatigued, stressed, uncomfortable" after days of illness, while patients elsewhere described the experience as unlike anything they had faced before.

Why This Outbreak Is Different

Cyclospora infections are notoriously hard to track. The parasite sheds intermittently in stool, meaning a single test can miss it, and it isn't part of standard lab panels for stomach illness, doctors often have to specifically suspect and order the test, CNN reported. That, combined with a two-week incubation period, means confirmed cases reflect infections from weeks earlier, complicating efforts to pin down a source.

Former CDC director Dr Robert Redfield told CNN that reduced federal surveillance funding has made early detection harder, warning that cutting such programmes is not in the country's interest since surveillance is key to early identification of outbreaks.

Comprehensively, only a handful of cyclospora outbreaks have ever crossed 1,000 cases in the past two decades - including a 1997 outbreak linked to Guatemalan raspberries and a 2019 outbreak tied to Mexican basil, according to CNBC, citing food-safety researcher Melanie Firestone.

Restaurants and Food Chains React

As speculation swirled online, several major food chains moved to reassure customers. Taco Bell said it had voluntarily and temporarily removed limited ingredients at select restaurants as a precautionary measure, while stressing that no official link to the chain had been confirmed. Chipotle's food safety officer said the company did not believe its sourced ingredients were connected to the investigation, CNN reported.

Salad chain Sweetgreen faced a wave of jokes online after a social media promotion was flooded with parasite-related comments, while the outbreak also became a talking point on food-focused social media, with dictionary publisher Merriam-Webster even weighing in with a lighthearted warning about salads.

Please avoid all salads, including word.

— Merriam-Webster (@MerriamWebster) July 15, 2026

How to Protect Yourself

Health officials say the parasite is unusually resistant to typical kitchen precautions. There is no evidence that vinegar rinses or commercial vegetable washes are effective, the CDC recommends scrubbing or cutting produce and washing it thoroughly under clean running water, since the parasite clings to outer surfaces. Officials in Michigan are advising residents to:

• Buy whole heads of lettuce instead of pre-washed, bagged salad mixes
• Remove and discard the outer two to three leaves before washing
• Cook fruits and vegetables where possible, since heat above roughly 70 degree celcius can kill the parasite
• Peel fresh produce after washing, where feasible

Anyone experiencing diarrhoea that persists for more than a few days is advised to consult a doctor and specifically ask about cyclospora testing, as it is not automatically included in routine screening.