A testing error by the FDA has cast doubt on the only laboratory evidence linking Michigan's massive cyclosporiasis outbreak to a specific lettuce supplier, leaving more than 1,000 sickened Oakland County residents without a definitive answer on what contaminated food to avoid.

The FDA disclosed July 19, PBS NewsHour reported, that a rapid screening test produced a false-positive result for cyclospora on a lettuce sample collected at the U.S. border. The sample came from Taylor Farms but was not part of the company's earlier recall. After a quality-control review confirmed the error, the FDA removed the finding from its website.

The retraction does not mean lettuce is cleared.

FDA Acting Food Chief Donald Prater told reporters July 20 that "FDA's traceback investigation and the outbreak data continue to converge on shredded iceberg lettuce from Taylor Farms' locations in central Mexico." The agency's epidemiological investigation remains active, and the Taylor Farms recall of 25 shredded lettuce and salad mix products, issued July 17, still stands.

The setback underscores how unsettled the investigation remains even as the outbreak has surpassed 1,000 cases in Oakland County and claimed Michigan's first two cyclosporiasis deaths reported this year. Gwen Biggerstaff, deputy director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, said July 31 that it's "not unusual for it to take a long time to identify the source for cyclosporiasis, if it's identified at all."

MDHHS continues to advise residents not to assume any specific product has been cleared unless health officials say so explicitly, and to keep favoring whole-head lettuce over pre-washed or bagged greens.

No additional recalls have been announced since July 17. The next MDHHS case-count update is expected Tuesday, August 4.