A college student with a positive result on purified protein derivative (PPD) testing (induration 12 mm) and a negative chest x-ray was treated with nine months of isoniazid. During this period, he was active and felt well. Pertinent history included living in Japan and traveling throughout Southeast Asia until age 4 years. He currently travels frequently to South America and continues to feel well. Does this patient require increased monitoring for TB?
—MELISSA RAUE, MMSc, PA-C, Pound Ridge, N.Y.

Your patient was treated for latent TB infection. Such treatment greatly reduces the likelihood that active TB will develop. In a previously infected person, treatment results in resistance to exogenous re-infection where the level of contagion is low because new mycobacteria are destroyed before significant multiplication occurs. If your patient spends considerable time in a situation where contagion is high, re-infection is certainly possible. His PPD will most likely remain positive even though he has been treated, and a repeat PPD should not be administered. If he spends more than six months in a country with high endemic levels of TB, has known exposure to person(s) with TB, or develops symptoms suggestive of TB, a chest x-ray should be obtained. If the chest x-ray is abnormal or the patient has symptoms, cultures for acid-fast bacilli should be ordered.
—Jo Ann Deasy, PA-C, MPH