Hundreds of patients and staff at three Chicago-area hospitals may have been exposed to tuberculosis by a contagious health care worker, officials said Friday.

About 300 staff and 150 patients may have been exposed at Children's Memorial Hospital, said Dr. Stan Shulman, the hospital's chief of pediatric infectious disease.

Seventeen patients may have been affected at Northwestern Memorial Hospital, officials said. The facility was evaluating another 100 patients with whom the health care worker, a doctor-in-training, might have had contact in November at its Prentice Women's Hospital.

Both hospitals said they were contacting affected patients and families.

Patients may also have been exposed at Evanston Hospital, according to the Chicago Department of Public Health. Officials there did not immediately return a call seeking comment.

The health care worker is a 26-year-old female resident in Northwestern's training program who had rotated through the three hospitals, the Chicago Tribune reported on its Web site.

Children's Memorial Hospital officials said they were responding with an abundance of caution and the public should know the chance of any transmission of tuberculosis is slim.

City and state public health officials and the Centers for Disease Control and Prevention were investigating.