U.S. health officials have declared the largest cyclospora food poisoning outbreak in the country's history over, according to recent reports. The U.S. Food and Drug Administration (FDA) stated it is confident that all recalled iceberg lettuce linked to this specific outbreak is no longer on the market. Nearly 13,000 reported cases of cyclospora were tied to the multistate outbreak, federal officials said. These cases represent the bulk of an unprecedented increase in the parasitic diarrheal illness this year. Cyclospora is a microscopic parasite that causes a condition known as cyclosporiasis, which leads to symptoms such as watery diarrhea, stomach cramps, and fatigue. Even with the outbreak officially over, several questions remain, including about its origin. The parasite is spread through human feces, and it still isn't clear how sewage could have contaminated enough food to sicken so many people. "This contamination can happen if produce is grown in soil or comes into contact with water that has been contaminated," said Ellen Shumaker, director of outreach for a North Carolina State University food safety program, Safe Plates. The outbreak has highlighted the challenges of tracing and preventing foodborne illnesses that originate from international sources. Since May 1, the government has received reports of nearly 20,000 lab-confirmed cases of cyclosporiasis, or more than 16 times the number reported during the same period last year. More than 6,100 suspected cases also have been reported. The worst previous year for infections in the U.S. was 2019, when about 4,700 illnesses were reported nationally. This year’s surge in cases was dominated by an outbreak in 21 states linked to iceberg lettuce. However, there are thousands of other cases that have not been linked to that outbreak. Michigan was the hardest-hit state, with the most reported cases and the two U.S. deaths tied to the outbreak. Cyclospora is a microscopic, spherical parasite that commonly causes watery diarrhea "with frequent and sometimes explosive bowel movements," according to the CDC. Outbreaks tend to occur most often in the late spring and summer. The illness, called cyclosporiasis, is less common than foodborne illnesses caused by other germs, including salmonella and E. coli. Many cases are never linked to a specific food or other source. In this outbreak, investigators initially focused on lettuce served at Taco Bell. Federal officials later identified Taylor Farms as the source of the lettuce, and the company recalled iceberg lettuce grown in central Mexico. The Taylor Farms recall involved thousands of packaged salad products combining iceberg lettuce with other vegetables. The products were shipped to major U.S. restaurant chains, including Yum Brands, which owns Taco Bell, Pizza Hut, and KFC. The FDA has ended its on-site inspections and sample collection at iceberg lettuce growers and the processing facility in Mexico, the agency said. Samples from the on-site inspections are pending analysis, the FDA said. The outbreak has cast a spotlight on a worsening problem: U.S. regulators are conducting fewer international inspections to catch contaminated produce before it lands on American plates.