Story highlights Illinois health officials report a fatal case of Elizabethkingia

Source of the outbreak remains unknown

(CNN) The Illinois Department of Public Health confirmed one case of Elizabethkingia in a resident who died earlier this year.

The individual had the same strain of Elizabethkingia that has been confirmed in 57 patients in Wisconsin since November. Eighteen of those individuals have died. All of those infected had "at least one serious underlying illness" and most are older than 65, according to the Wisconsin of Health Services.

It's unknown whether the deaths were caused by the infection, the existing health conditions or the combination of both.

The number of cases in Wisconsin may continue to rise as the state health department continues to investigate possible cases.

Last month, the Michigan Department of Health and Human Services reported a case of the infection in their state. At the time, CDC spokesman Tom Skinner told CNN the Michigan case was not a complete surprise, given that health departments across the country were asked to be on the lookout for Elizabethkingia infections after the outbreak in Wisconsin was identified.

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