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Control Interventions

TB control aims to break the chain of transmission by (1) reducing the number of infectious sources in the society by rapid diagnosis and adequate treatment of TB cases, and (2) preventing the progression from infection to disease by diagnosis and treatment of LTBI (Figure 8 and Figure 9). There is a hierarchy here in that the identification and treatment of active disease should have absolute priority. Spending a lot of resources on LTBI treatment is a waste if active tuberculosis is not adequately cared for. This means that favorable conditions must exist for passive case finding, including reducing the barriers to care for all those suspected of carrying TB infection, including illegal and/or uninsured individuals. In addition, active case finding must focus on identified risk groups for tuberculosis, such as recent immigrants and prisoners. Cohort analysis of treatment outcome provides an essential element of TB control program monitoring. High default and failure rates should lead to problem analysis and appropriate action. In countries where active cases are properly taken care of, diagnosis and treatment of LTBI must be introduced to “speed up” the elimination of TB.

This brings us to the role of the tuberculin skin test, which is only of limited importance in source reduction but of utmost importance as a tool in the “prevention of breakdown” process (Figure 8). Treatment of LTBI reduces the pool of latently infected individuals and thus the pool of future TB sources.

In addition to the control interventions mentioned above, infection control measures are increasingly important. The overlap of the HIV and the TB epidemics in some groups and settings requires that sufficient measures be taken to prevent transmission from identified and unidentified TB sources.

The Role of the Tuberculin Skin Test (TST)

Targeted tuberculin testing for LTBI is a strategic component of TB control in low-prevalence countries that identifies persons at high risk for developing TB and who would benefit by treatment of LTBI. Persons with increased risk for developing TB include those who were recently infected and those who have clinical conditions that are associated with an increased risk for progression of LTBI to active disease (7).

Sometimes, for example, during contact investigations or in patients with symptoms—a positive skin test result (combined with x-ray and sputum examinations) identifies patients who have already developed active TB. In such cases the tuberculin skin test supports either active or passive case finding rather than LTBI diagnosis.

Knowledge of tuberculin test sensitivity and specificity, as well as understanding of the predictive value of the test in different populations, are required to properly target and interpret skin tests. False positive tests occur in persons who have been infected with non-tuberculous mycobacteria and those who have received BCG vaccination. For this reason targeted testing should only be conducted among groups at high risk and discouraged in those at low risk. Causes for false negative and false positive reactions are listed in Table 2.

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