Federal investigators say a sample of shredded iceberg lettuce tested positive for cyclospora, adding a significant lead to a growing foodborne illness investigation. The finding comes as health officials examine a multistate outbreak linked to the parasite.

According to the report, the lettuce sample was produced by a Taylor Farms subsidiary in Mexico. The positive test does not by itself answer every question about the outbreak, but it gives regulators and public health officials a clearer focus as they work to trace the source of infections.

The outbreak has sickened more than 1,600 people across the United States, underscoring the scale of the public health concern. Cyclospora is a parasite that can cause severe gastrointestinal illness, and the investigation appears to be centered on whether contaminated lettuce played a role in spreading the infections.

The FDA’s reported finding adds momentum to the broader inquiry into how the parasite entered the food supply and where affected products may have been distributed. Officials are continuing to review evidence tied to the outbreak as the national case count grows.