disease by treating individuals with latent infection to reduce the risk of disease. The Advisory Council for the Elimination of Tuberculosis (ACET) included expanded targeted testing and treatment of latent infection among the highest-priority activities for tuberculosis control programs (CDC, 1999). Recently published guidelines from the Centers for Disease Control and Prevention (CDC) and the American Thoracic Society will provide a framework for increased attention to targeted screening and will recommend new regimens for the treatment of tuberculosis infection (American Thoracic Society and CDC, 2000). As recommended by the guidelines and by ACET, local epidemiological conditions will guide the testing effort, but increased national attention will be needed in three areas. First, as noted in Chapter 2 , tuberculosis among foreign-born individuals accounts for an increasing proportion of U.S. tuberculosis cases, and slightly more than half of these cases occur within the first 5 years of the arrival of foreign-born individuals in the United States. Targeted tuberculin skin testing of newly arrived immigrants before arrival in the United States with adequate treatment for those with latent infection once they arrive could prevent a significant number of cases. Second, an outbreak of tuberculosis associated with a prison led to the recognition of the resurgence of tuberculosis in the United States, and screening for infection and treatment of latent infection should be mandatory in these settings. Finally, by challenging traditional concepts about contact investigations and expanding the definition of close contacts to include social contacts and others previously thought to be at lower risk of infection, many more recently infected individuals who are at an increased risk of developing tuberculosis will be identified. This chapter provides a brief background on the rationale for the treatment of latent infection and addresses these priority areas for the prevention of tuberculosis.
Shortly after the discovery of isoniazid in 1952, the potential of this highly bactericidal drug to prevent tuberculosis was explored. A series of trials summarized in a review by Ferebee (1970) showed that the effectiveness of isoniazid for the prevention of tuberculosis ranged from 92 percent in an outbreak among Dutch sailors, in which adherence to the regimen was strictly enforced (Veening, 1968), to 26 percent in a Tunisian community-based study in which the rate of adherence to the isoniazid regimen was estimated to be only 25 percent or less. A study of 3-, 6-, and 12-month regimens showed that a 12-month regimen was the superior regimen (International Union Against Tuberculosis, 1982) and Comstock (1999) recently presented an analysis that showed that a regimen of at least 9 months likely gives maximum protection.