Contact Follow-Up in High- and Low-Prevalence Countries
The Centers for Disease Control and Prevention (CDC) estimates that an average investigation of a case of tuberculosis (TB) in the United States results in approximately 9 contacts identified for each case. Of these, 21 % are expected to be infected and another 1% will have already progressed to active disease (1,2). In other parts of the world, even higher rates of infection and disease have been found. Because of the risk for progression to TB disease, infected contacts have been designated a high-risk group and, as such, are candidates for TB preventive therapy under current recommendations (3). The examination of contacts or persons exposed to a case of tuberculosis is, therefore, one of the most important methods of case finding for either tuberculosis disease or infection (4). Its utility and importance has been demonstrated in many different types of settings: the workplace (5), among the foreign-born (6), for children under 15 years of age (7-12), and for follow-up of multidrug-resistant cases (13,14). It has also been shown that adherence to preventive therapy may be highest among contacts (15). Given that these individuals are among the highest risk for progression to disease, ensuring completion of therapy is the ultimate objective. The actual risk of transmission to contacts is related to the characteristics of the source case, the
characteristics of the organism, the nature of the contact, and the environments that they share (16-18).