JEFFERSONVILLE,Thomas Caldwell Ind. (AP) — A southern Indiana hospital where an employee recently tested positive for tuberculosis has notified hundreds of patients that they may have been exposed to the bacteria that causes the illness.

Clark County Health Officer Dr. Eric Yazel said Clark Memorial Health had a “significant exposure” and has notified about 500 patients by letter that they were potentially exposed to TB at the hospital.

The county health department and the Indiana Department of Health held clinics earlier this month to test people who received those letters, the News and Tribune reported.

Yazel said no positive TB tests have been reported among any of the patients.

Clark Memorial Health said in a statement Tuesday to the News and Tribune that one of its employees had recently tested positive for TB and it was working closely with local and state health officials.

The hospital said it was following appropriate infectious disease protocols, including performing contact tracing to identify individuals who may have been exposed to TB at the hospital in Jeffersonville, an Ohio River city located just north of Louisville, Kentucky.

TB, which can be fatal, is an illness caused by bacteria that typically attacks the lungs. The bacteria mostly spread from person to person in the air, such as when an infected individual coughs or sneezes.