Lettuce supplied by Taylor Farms that initially tested positive for Cyclospora was a false positive, according to the Food and Drug Administration.
The agency said laboratory experts re-reviewed the sample because of the complexity of detecting Cyclospora and determined the result "does not represent true amplification" and should not be considered a confirmed positive.
There are now no confirmed positive product test results for Cyclospora, as investigators continue trying to determine the source of an outbreak that has sickened more than 1,500 people.
Taylor Farms said the FDA apologized after informing the company that the initial test result was incorrect.
"To be clear, at this moment, FDA has not identified a single positive product test result for Cyclospora," the company said in a statement.
Taylor Farms said it voluntarily recalled iceberg lettuce grown and processed in central Mexico out of an abundance of caution after receiving the FDA's initial notification. The company said the recall was limited to iceberg lettuce from central Mexico and does not involve any other Taylor Farms products, including products sold under the Taylor Farms brand.
The outbreak has sickened people in multiple states, including Indiana, Kentucky, Michigan, Ohio and West Virginia.
Cyclosporiasis is a foodborne illness caused by the microscopic parasite Cyclospora. People typically become infected by consuming contaminated food or water, particularly fresh produce.
Common symptoms include diarrhea, frequent bowel movements, loss of appetite, weight loss, stomach cramps, bloating, increased gas, nausea and fatigue.
