Most of the patients who may have been exposed are children.
The hospitals affected are Children's Memorial, Northwestern Memorial and Evanston.
Officials from all three hospitals are confident their approach to this matter will prevent an outbreak among those who came into contact with the female doctor-in-training who came down with TB. Still, at least 247 people and their families have been notified that they should be on the lookout for infection.
A concerned group of public health officials, representing the affected institutions and the city, said the sheer number of patient contacts the infected Northwestern University student doctor had while she was contagious required public notification.
"In an abundance of caution these institutions are trying to respond even though the risk is minimal and that has actually made the numbers higher but we all agree it is very important to be cautious," said Dr. Susan Gerber, Chicago Dept. of Public Health.
On Tuesday, officials say the student doctor was diagnosed with the tuberculosis bacterium and hospitalized. They don't know how she got it and there are no outbreaks of the disease now in Chicago. From early February to mid March she had been on duty in the three institutions, as part of her training. The officials say she had direct contact with many children, including those in the neo-natal units at Children's Memorial and Evanston Hospital.
Testing so far has shown no patients -- or people in close proximity to them -- has TB.
"This situation is a cause for concern, but not alarm. The case of TB has been identified, isolated and treated," said Dr. Terry Mason, Commissioner, Chicago Dept. of Public Health.
The 26-year-old student doctor, whose identity has not been released, is now resting at home. People entering Children's Memorial on Friday night had mixed views on whether TB poses a danger now.
"It concerns me. They're going to be testing a lot of the patients and a lot of staff. We just have to wait and see," said Tracy Cronin.
"If we were aware of the situation, maybe we could have taken a precaution to not have the kids here, so it is a major concern," said Chloe Clayborn.
The investigation involves the Centers for Disease Control and Prevention and the Chicago, Cook County and Illinois departments of public health.
If you believe your child or you may have come into contact with this physician over the last five months please call 312-746-4835.
For information on TB, including symptoms and treatment, please visit the American Lung Association's Web site.