Positive PPD and chemoprophylaxis for tuberculosis infection

The appearance of an indurated area of 5 mm or more 48 to 72 hours after administration of purified protein derivative (PPD) is considered a positive reaction in persons who have recently had close contact with an individual with active tuberculosis, in persons with radiographic findings consistent with a past history of tuberculosis or in persons with known or suspected human immunodeficiency virus infection. Ten or more millimeters of induration is considered a positive reaction in persons at increased risk of tuberculosis. Induration of 15 mm or more is considered a positive result in all other persons. Candidates for a six-month course of isoniazid include persons under age 35 who are recent converters and have induration of 10 mm or more and persons over age 35 with 15 mm or more of induration. Patients with HIV infection and those with radiographic evidence of previous tuberculosis should receive 12 months of therapy. A regimen of pyrazinamide and either ethambutol, ofloxacin or ciprofloxacin is recommended for contacts of patients with multidrug-resistant tuberculosis.