About 60 people from Parkville High School may have been exposed to tuberculosis toward the end of the school year, the Baltimore County Health Department said Friday, after an unidentified person — described only as a "young lady" — was diagnosed with the infectious disease last month.

Letters were sent Friday to the potential contacts — staff and students — urging them to get tested by their doctors or during a free clinic being offered at the school from 8 a.m. to noon Aug. 13. The results will determine whether wider testing is needed.

"It's an airborne disease. A person with active TB, when they cough, they sing, they laugh, whatever, they can spread bacteria into the air," Dr. Barbara McLean, director of the Baltimore County Health Department's Bureau of Prevention, Protection and Preparedness, said during a news conference.

Casual contact would not likely result in infection, McLean said: "A person needs to have very close contact for a prolonged period of time to breathe in the bacteria. It's not an easily communicable disease."

No information was available on how the female patient might have contracted the disease.

According to the Centers for Disease Control and Prevention, there were 10,528 tuberculosis cases in the United States in 2011, the most recent year for which data are available. In Maryland, there were 224 cases last year; 29 of them were in Baltimore County.

Tuberculosis typically infects the lungs and can be fatal if untreated. It remains a leading killer around the world, taking 1.4 million lives annually, according to the Johns Hopkins Center for Tuberculosis Research. But most cases in the U.S., which has made a concentrated effort to eradicate the disease, are cured through a lengthy antibiotic regimen that lasts six months or more.

The disease poses more of a danger to older people with other ailments than it does to children and younger adults, said Richard E. Chaisson, director of the Hopkins center.

"There tends to be a very high anxiety level when it involves children in a school that's often disproportional … to the real risk," Chaisson said.

Gregory W. Branch, director of the county's Health and Human Services Department, said the agency was notified of the diagnosis July 17. Its investigation began with the patient's family and is now widening to the greater Parkville community.

"We're actually on top of this, and we're doing a very, very quick job in this," Branch said.

After exposure, it usually takes about two months for the disease to show up in tests, Branch said.

"You can do the testing early, but you'd have to do it again," he said. "In essence, we are right at the perfect time."

No other cases have been identified. Questions should be directed to the Baltimore County Department of Health at 410-887-2711.

tricia.bishop@baltsun.com

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