By Jacqueline Howard, CNN
(CNN) — Cases of diarrhea caused by the parasite cyclospora continue to climb, and with the threat of weekslong illness and no certainty about the source, it’s easy to wonder: Is there anything in the produce aisle that’s safe to eat?
The outbreak has risen to more than 3,000 cases in Michigan and Ohio, and linked to cases in West Virginia and Kentucky. Michigan health officials said their investigation suggests that lettuce or salad greens may be the culprit, but other foods can’t be ruled out — and no specific type, grower or supplier has been identified as the source.
Nationally, more than 7,000 cases have been confirmed or are under investigation, in 34 states since May 1, according to the US Centers for Disease Control and Prevention. It’s not clear which states are seeing cases connected to the large outbreak in the Midwest.
While Michigan health officials urge shoppers to be especially careful when purchasing and eating lettuce and greens this summer, federal health officials are emphasizing staying up to date on health alerts and using standard safety practices when washing food.
“Cyclospora is a very interesting organism. It’s a parasite, so it’s historically been linked to outbreaks in the past, usually foodborne outbreaks,” said Dr. Nuwan Gunawardhana, a hospital epidemiologist and physician who specializes in infectious diseases at Columbia University Irving Medical Center.
“It’s not really considered contagious from person to person,” he said. “When we’re talking about foodborne outbreaks with cyclospora, it’s a very hardy organism, and so it has the ability to adhere to the surfaces very, very well with our fresh produce and fruit.”
Who’s most at risk
Cyclosporiasis is the intestinal illness caused by the microscopic parasite cyclospora, and symptoms typically develop about two days to two weeks after exposure, including prolonged watery diarrhea, stomach cramps, nausea, fatigue, loss of appetite and weight loss. Although the infection can be treated with a combination antibiotic, the illness can last weeks if left untreated and may lead to dehydration.
About 1 in every 11 cases has been hospitalized, according to data reported to CDC. No deaths have been reported.
“Those most at risk are young children, elderly individuals and immunosuppressed people,” said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center.
“In most other healthy people, disease is often mild,” he said. “While it makes sense to take precautions, particularly for people at higher risk, there’s no reason for panic at this stage.”
But for people wondering what foods are safe to eat, there are some simple steps to take, both at the grocery store and at home.
Foods to avoid
When shopping for lettuce or other greens, experts recommend avoiding precut or packaged items and selecting whole, uncut produce instead, because it typically undergoes less handling.
Bagged salad mixes and kits have been specifically linked to previous cyclospora outbreaks in the United States and Canada, according to Michigan health officials.
On Tuesday, fast food chain Taco Bell also said it’s removing some ingredients from its menu at some locations as a precaution.
“It’s probably a good idea to avoid bagged lettuce products and bagged salad products for now. And if those are desired, then to rewash them at home, even if they come prewashed, because the actual source of the outbreak is not yet known,” Barouch said.
Raspberries, basil, salad mixes — like vegetable trays and coleslaw — cilantro, berry and fruit mixes, lettuce and snap peas have all been linked to outbreak