The infection that killed an Illinois scientist may be connected to bacteria he researched that causes the plague, the University of Chicago Medical Center said.

The university said Saturday that its researcher studied the genetics of harmful bacteria including Yersinia pestis, which causes the illness. He died Sept. 13. His name and age have not been released.

The medical center said the bacteria he worked with was a weakened strain that isn't known to cause illness in healthy adults. The strain was approved by the Centers for Disease Control and Prevention for laboratory studies.

An autopsy found no obvious cause of death but did find the presence of the bacteria. More tests are planned. No other illnesses have been reported.