Health officials in three states in cooperation with the Centers for Disease Control and Prevention are hoping to track down people who might have been in contact with a patient with a rare, drug-resistant form of tuberculosis.

The unnamed female patient, now under treatment at the National Institutes of Health, had an active, infectious case of the rare type of TB known as extensively drug-resistant tuberculosis or XDR-TB when she arrived at Chicago O'Hare International Airport on a flight from India in April, officials said.

XDR-TB is resistant to the many drugs normally used to treat TB.

Before seeking treatment for her illness, the woman spent seven weeks traveling in Illinois, Missouri and Tennessee, officials said.

After initial treatment in a Chicago hospital, she was transferred to the NIH Clinical Center in Bethesda, Maryland, in special ground and air ambulances. She is reportedly in stable condition in an isolation unit there.

Meanwhile, state and federal health officials have begun efforts to obtain the passenger lists of her flight into Chicago and to identify people who may have come into contact with her on her travels after arriving.

They are encouraging people to consult with a health care provider if they believe they've been in contact with someone displaying common symptoms of TB, which can include a bad cough, chest pain, fever and fatigue.

"CDC will obtain the passenger manifest for that flight from the airline and will begin a contact investigation," said CDC spokesman Thomas W. Skinner. "Although the risk of getting a contagious disease on an airplane is low, public health officers sometimes need to find and alert travelers who may have been exposed to an ill passenger."

The XDR-TB form of tuberculosis is mostly seen in China, India, sub-Saharan Africa, Pakistan and Russia, experts say.

It is rare in the United States, with just 63 cases diagnosed between 1993 and 2011, compared with more than 300,000 cases of the more usual type of TB in that same period.

In developing countries in Asia and Africa, the common type of TB is a serious health problem, with the World Health Organization reporting nine million cases in 2013, causing 1.5 million deaths.

TB is not contagious by touch, but is spread through the air when an infected person sneezes, coughs or speaks. TB bacteria can remain dormant in the body for years before it becomes active and thus infectious.

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