Health officials have detected two cases of the same strain of E. coli O157:H7 in Manitowoc County, Wisconsin, and are conducting an investigation to determine the source of the bacteria.

“We have two cases of E. coli that have the same fingerprint,” Amy Wergin, public health nurse manager for the Manitowoc County Health Department, told the Herald Times Reporter. “We are trying to discern what the link is between the two,” Wergin said. “Right now, these are the only two in the nation with this fingerprint.”

The two illnesses occurred in March, and there have been no other reported infections with this strain of E. coli in the country since then, according to Wergin.

The same strain cropped up in four cases about a year ago in May of 2012. Two cases were in Manitowoc, one was in Brown County, WI and one was in Colorado.