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A female patient with an extremely hard-to-treat form of tuberculosis is being treated at the National Institutes of Health outside Washington, D.C., and federal and state officials are now tracking down hundreds of people who may have been in contact with her.

The woman traveled to at least three states before she sought treatment from a U.S. doctor. While TB is not easily caught by casual contact, extensively drug resistant (XDR) TB is so dangerous that health officials will have to make a concerted effort to warn anyone who may be at risk.

“The patient was transferred to the NIH via special air and ground ambulances,” the NIH said in a statement.

“The patient was transferred to the NIH via special air and ground ambulances."

“The patient is staying in an isolation room in the NIH Clinical Center specifically designed for handling patients with respiratory infections, including XDR-TB. The National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH, is providing care and treatment for the patient in connection with an existing NIH clinical protocol for treating TB, including XDR forms. NIAID has treated other XDR-TB patients in the past under this protocol," the NIH said.

These special isolation rooms usually control air flow to prevent germs from escaping into the rest of the hospital or outside.

The patient, who isn’t being identified in any way, may face months or even years of treatment. Ordinary TB is hard to treat and requires, at a minimum, weeks of antibiotics. XDR-TB resists the effects of almost all the known TB drugs. Sometimes patients have to have pockets of infection surgically removed.

Only about a third to half of cases can even be cured.

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It’s not clear why the patient traveled so much before seeking treatment, the Centers for Disease Control and Prevention says.

“The patient traveled in April from India to the United States through Chicago O’Hare airport,” the CDC said in a statement provided to NBC News.

“The patient also spent time in Missouri and Tennessee. Seven weeks after arriving in the United States, the patient sought treatment for and was diagnosed with active TB.”

She was isolated in a suburban Chicago hospital before she was sent to NIH.

CDC and NIH are testing the patient to see what drugs may help her.

“Besides concerns about community contacts, the patient flew from India to the United States. CDC will obtain the passenger manifest for that flight from the airline and will begin a contact investigation. 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,” CDC said.

CDC takes these cases very seriously. In 2007 Andrew Speaker, an Atlanta lawyer with multi-drug-resistant tuberculosis, was arrested and forcibly isolated under federal order after he defied CDC advisories and flew out of the country to get married.

XDR-TB is very rare in the U.S. CDC says it got reports of 63 cases between 1993 and 2011.

"TB bacteria are put into the air when a person with TB disease of the lungs or throat coughs, sneezes, shouts, or sings," CDC says. "These bacteria can float in the air for several hours, depending on the environment. Persons who breathe in the air containing these TB bacteria can become infected."

“The patient traveled in April from India to the United States through Chicago O’Hare airport."

People with lowered immunity, especially HIV patients, are most at risk.

“All travelers should avoid high risk settings where there are no infection control measures in place. Documented places where transmission has occurred include crowded hospitals, prisons, homeless shelters, and other settings where susceptible persons come in contact with persons with TB disease,” CDC advises.

The average cost of treating multidrug-resistant TB is $134,000, compared to $17,000 for a normal case. That can shoot up to $430,000 for an extensively resistant case. It’s not clear who will pay for this patient’s treatment.

Nine million people are infected with TB every year, including 9,000 people in the U.S.