Source of E. Coli Outbreak at Michigan State University Unknown

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It's likely that more Michigan State University students than first thought were sickened in a recent E. coli outbreak.

The Detroit News reported Friday that six cases have been confirmed while another 13 students are considered probable victims. That raises the number of students associated with the outbreak to 19, up from about 10 earlier in the week.

The students who are considered probable victims all had cases of bloody diarrhea within the last week. That's the most common symptom of E. coli contamination.

Federal, state and Ingham County health officials are investigating.

"So far, there is no clear pattern that's jumping out at us that would account for all the cases," Dean Sienko, head of the Ingham County Health Department, told the newspaper.

Health officials hope to nail down the possible sources once testing confirms which cases are part of the same outbreak.

Six of the seven people hospitalized with the illness had been released as of Thursday.

Michigan State officials sent out an alert this week encouraging students to step forward if they have experienced gastrointestinal illness, particularly bloody diarrhea.