Barely days old, hundreds of babies in Chicago may already have been exposed to tuberculosis.
"We are investigating a situation in which a physician may have unknowingly exposed patients and hospital co-workers," Dr. Terry Mason of the Chicago Public Health Department said Friday.
"The one thing that makes this investigation stand out is its size and its scope," Mason added.
Officials said the 26-year-old resident, whose name has not been released, was on rotation at three different Chicago-area hospitals for the last 10 months, working with at least 150 children and infants at Children's Memorial Hospital; 100 patients, including 17 newborns at Northwestern Memorial Hospital; and an additional 80 babies at Evanston Hospital's Infant Special Care Unit.
So far, officials said, not a single patient has tested positive for tuberculosis -- although some of the most vulnerable of those exposed may receive preventive antibiotics.
Dr. James McAuley, a pediatrics infectious diseases expert at Rush University Medical Center, said young children are not necessarily more at risk for tuberculosis, but the danger lies in what happens once they're infected.
"Often they will go right from infection to TB throughout the body, including meningitis, which can be very dangerous," McAuley said.
However, tuberculosis is not easy to catch, McAuley said. The disease, mostly spread through coughing and sneezing, requires extended exposure to result in infection.
Once the resident was diagnosed, officials at the affected hospitals immediately took action.
"We are taking this very seriously," said J.P. Gallagher, president of Evanston Hospital.
Staff from all the hospitals involved have identified and notified all patients, families and staff members that might have been exposed.
In addition, Dr. Stanford Schulman, chief at the Division of Infectious Diseases at Children's Memorial Hospital, told ABC News tuberculosis screenings are available.
"We've offered skin testing and several parents have come today for skin testing," he said.
The source of the doctor's infection is still a mystery. Officials speculate she may have been infected while working in an African H.I.V. clinic in 2007 or during subsequent rotations in the United States.
"She was screened, as would be expected, when she started last July and was negative on the screening," McAuley said.
Doctors said she may not have realized just how sick she was until the more severe symptoms, such as weight loss, weakness, chills and fever, set in.
She was treated at Northwestern Memorial Hospital and released.
"When the physician, and the public health department, and we all believe that its safe for her to resume her routine activities at the hospital, of course she will be back," Schulman said.