Health officials investigating the large outbreak of diarrhea caused by the parasite cyclospora say they have “very strong” evidence that shredded iceberg lettuce supplied by Taylor Farms is the likely source, despite a false positive test for the parasite over the weekend.

“FDA’s traceback investigation and outbreak data continue to converge on shredded iceberg lettuce from Taylor Farms locations in Central Mexico,” the US Food and Drug Administration said in a statement Monday.

“Protecting the American public remains our highest priority. We encourage the public to continue to avoid all products listed in Taylor Farms voluntary recall.”

On Sunday, Taylor Farms recalled iceberg lettuce shipped to 27 states.

Taylor Farms is a major produce supplier in the US, selling lettuce and bagged salad kits under several private store labels. However, the company did not mention specific retailers, restaurants or product names in its recall notice.