US explosive diarrhea outbreak grows as officials hunt mystery source

A US explosive diarrhea outbreak tied to the cyclospora parasite has spread to 34 states and sickened nearly 7,000 people, yet federal and state investigators still cannot name the contaminated food behind it. Lettuce and salad greens are the leading suspect, but no grower, supplier or brand has been confirmed. The main symptom is frequent, watery diarrhoea that can last weeks. With no recalls issued and traceback still under way, the mystery has left millions of Americans asking what is safe to eat.

Key Takeaways

• Nearly 7,000 cyclosporiasis cases have been confirmed or are under investigation in 34 states since May 1, per the CDC.
• Michigan leads with more than 3,300 cases; lettuce and salad greens are a leading suspect, but no supplier is confirmed.
• Experts say multiple contamination points and a 1–2 week incubation period are complicating traceback.
• About 1 in 11 cases has been hospitalised; no deaths have been reported.
• Cooking produce to 158°F kills cyclospora; washing alone cannot fully remove it from leafy greens.

Why can't officials find the source of the outbreak?

Cyclosporiasis spreads through contaminated food or water, not person-to-person contact. The BBC reports that people typically fall ill one to two weeks after exposure — far longer than most foodborne bugs — making it harder to trace what they ate.

Testing for cyclospora is also complex. Experts told the BBC you would need truckloads of suspect produce washed and concentrated before labs could detect the parasite. Given the outbreak's scale, public health officials believe multiple contamination points in the food supply may be involved.

Michigan health officials identified lettuce and salad greens through patient interviews, but no specific grower, supplier or brand has been named. The FDA is conducting traceback on multiple produce items while the CDC continues its outbreak investigation.

How many people have been affected?

The CDC said Tuesday that more than 7,000 cases have been confirmed or are under investigation across 34 states since May 1. Michigan is hardest hit with more than 3,300 cases, followed by New York state, according to the BBC.

A large Midwest cluster appears linked across Michigan, Ohio, West Virginia and Kentucky. Symptoms include prolonged watery diarrhoea, cramps, nausea and fatigue. CNN reports about 1 in 11 cases has been hospitalised, though no deaths have been reported.

What foods should Americans avoid right now?

Without a confirmed source, no product has been recalled. Michigan officials suggest lettuce may be involved, while CNN notes bagged salad mixes and kits have been linked to past US cyclospora outbreaks.

Experts recommend avoiding precut or packaged greens when possible and selecting whole, uncut produce instead. People with weakened immune systems may want to skip raw produce until a culprit is identified. Cases like this often raise broader questions about how investigators crack unsolved public health mysteries.

How can you protect yourself at home?

Michigan health officials recommend buying whole heads of lettuce, discarding the outer two to three layers and thoroughly washing inner leaves under running water. The CDC cautions that chemically disinfecting produce may not fully eliminate cyclospora.

Cooking food to an internal temperature of 158°F or higher kills the parasite, making cooked vegetables a lower-risk option than raw salad. Experts also warn against washing produce with soap, bleach or chlorine, as cyclospora resists chlorine and residues can be harmful.