Lab tests have confirmed at least three dozen people around the St. Louis area have the same strain of E. coli first reported in the region in late October.

A month after the initial report on Oct. 24, health officials are still unable to identify the source of the contamination.

The St. Louis County and Missouri health departments turned to federal officials in early November to find the source. Marianna Naum, a policy analyst for the Food and Drug Administration said the investigation is still ongoing.

“We don’t know if USDA or FDA will ultimately handle this because we still don’t know what commodity or food is responsible,” Naum said. “The CDC is the lead agency on the case now.”

Meanwhile, officials at the Centers for Disease Control and Prevention said on Nov. 22 that they are waiting for the FDA to complete traceback investigations based on information the CDC provided to the FDA.

Doctoral epidemiologist Laura Gieraltowski is heading the investigation for the CDC. She said information from CDC’s interviews with patients about what food they had eaten before becoming ill had been sent to FDA for follow up.

“FDA is working on tracing back certain salad bar items,” Gieraltowski said. “They are interviewing suppliers and going through distribution records. No source has been found yet.”

Initially officials thought food from salad bars at St. Louis area Schnucks grocery stores might be linked to the outbreak because early on some patients reported having eaten food from there. However, 53 food samples from several Schnucks salad bars and two samples from patients’ homes who said they bought food from the salad bars all tested negative for E. coli.

In an attempt to solve the mystery, the CDC set up a special call center and randomly interviewed residents who live near the E. coli victims. Gieraltowski said such call center surveys are “occasionally” done when an outbreak investigation requires a control factor.

She said at any given time the CDC is investigating about 40 food-related illness outbreaks in the U.S. She added that the scope and length of the St. Louis investigation has not been out of the ordinary.