(Jan. 12, POSTED 12:00 p.m. CST) The U.S. Food and Drug Administration on Jan. 12 issued a news release saying that federal and state officials are now a step closer to identifying the source of an E. coli outbreak that sickened more than 80 people late last year.

The FDA said illnesses tied to an E. coli O157:H7 outbreak in November and December at Taco John’s restaurants in Iowa, Minnesota and Wisconsin may have been the result of lettuce contaminated by material from a dairy farm near where the lettuce was grown.

If and how the material tainted the lettuce are questions yet to be answered, but the FDA said additional samples would be taken and that the investigation remains ongoing.

The agency said it, and the state of California, worked with state health officials in the three states that experienced the outbreak to DNA-match the specific E. coli strain in the Taco John’s case with two samples obtained from dairy farms near a lettuce field in California’s Central Valley.

Previous epidemiological studies by health officials during the outbreak resulted in the likelihood that shredded iceberg lettuce was the vehicle for transmission of the E. coli.

The FDA said it was able to target specific lettuce growing regions based on traceback records acquired from the lettuce processor that processed Taco John’s lettuce. Despite the DNA match, the FDA said there may be other possible sources of the contamination.