A Harvard undergraduate was diagnosed with tuberculosis by University Health Services several weeks ago, and roughly forty students at risk for exposure have been asked to submit to a TB skin test, according to information provided by UHS and the Cambridge Public Health Department.

The student, whose identity has not been made public, was released earlier this week after public health officials determined he or she was no longer infectious, according to an e-mail from Jennifer B. Anderson, a UHS Communications Officer.

Anderson also said that no other students have presented signs of an active TB infection.

“We know of no other confirmed cases of TB at Harvard,” she wrote.

But among those students who have been asked to submit to a Mantoux Test, which determines whether an individual has produced antibodies to the tuberculosis bacterium, some have tested positive, according to Kate Matthews, a nurse in the Cambridge Public Health Department.

Matthews stressed that a positive skin test does not mean an individual is actively sick with TB.

“What it means to have a positive skin test is that you’ve had the TB germ in your body at one point. It doesn’t mean you’re sick or contagious,” she said, noting that roughly one in three individuals worldwide have been exposed to TB at some point in their lives.

According to Eric Rubin, a professor of immunology and infectious diseases at Harvard Medical School, those students who test positive for TB without showing signs of illness will be recommended to start a nine month regimen of daily antibiotics.

Rubin also said that there was another case of tuberculosis at a Harvard graduate school within the past two years.

But Matthews, who noted that there are roughly eight to twelve cases of tuberculosis in Cambridge each year, said that this was the first case among undergraduates in “a long time.”

—Staff writer Evan T. R. Rosenman can be reached at erosenm@fas.harvard.edu.