A woman with a rare and potentially fatal drug-resistant form of tuberculosis visited Illinois, Missouri and Tennessee this spring, and U.S. and Illinois health officials were working on Tuesday to identify people who may have been exposed to her.

The woman arrived at Chicago's O'Hare International Airport from India in April. She sought treatment for tuberculosis seven weeks later, officials said.

Now in stable condition at the National Institutes of Health Clinical Center in Maryland, the patient initially was held in respiratory isolation at a suburban Chicago hospital, Tom Skinner, spokesman for the U.S. Centers for Disease Control and Prevention, said in a statement.

The risk of getting a contagious disease on an airplane is low, according to the statement.

"This is a very serious illness, but it's difficult to transmit," Skinner said in a telephone interview. "You have to have prolonged close contact with someone with active tuberculosis to get it."

Anthony Fauci, director of NIH's National Institute of Allergy and Infectious Diseases, told WTOP radio in Washington on Tuesday that the patient's contacts are being tracked down by Illinois and CDC health officials.

"People should not be concerned about this," Fauci said.

The CDC will obtain the list of passengers on the patient's flight from the airline and close contacts will be tested, Skinner said.

Tuberculosis is spread from person-to-person through the air when an infectious person coughs, sneezes or speaks, according to the CDC. People in the vicinity can breathe in the bacteria and become infected.