The Weber-Morgan Health Department confirmed Monday four people were infected with E.coli bacteria in June following a conference held at Orion Junior High in Harrisville.

The Deseret Morning News reports that three of those people have developed a more severe case of hemolytic uremic syndrome.

Based on its own investigation, the department said the likely source of the contamination was iceberg lettuce prepared at a Wendy’s restaurant in North Ogden, which was one of the caterers for the conference.

"What we’re trying to determine is what happened," said Denny Lynch, spokesman for Wendy’s Restaurants in Denver. "Clearly we are very concerned with this incident."

The conference was attended by more than 300 people, but only a handful reported getting sick. No other cases among those who attended have reported to have E.coli.

Wendy’s Restaurants is trying to contact those who were apparently affected by the contaminated lettuce and do what they can for them.