Tuberculin testing to detect latent tuberculosis in developing countries.

Despite the multiple studies done over several decades that have established the utility of the tuberculin skin test (TST) for the diagnosis of latent tuberculosis, the test is rarely used in developing countries experiencing a resurgence of tuberculosis. Nevertheless, several clinical trials have found that treatment of HIV-positive or HIV-negative persons with latent tuberculosis is effective in the prevention of the clinical activation of tuberculosis. Clinicians commonly justify their failure to diagnose and treat latent tuberculosis with the belief that BCG vaccine, even when it is used in infancy, will cause false positive reactivity in the TST. The important study by Gustafson and colleagues from Guinea-Bissau in this issue of the journal refutes this belief. In this study only persons with a history of BCG who also had household contact with an active case of tuberculosis had increased rates of TST positivity. Although the current emphasis is on directly observed therapy, short course (DOTS) to control tuberculosis is necessary and critically important, it is not always sufficient to control the tuberculosis epidemic in some countries with major epidemics of HIV. In many of these countries, early diagnosis of active tuberculosis and prevention of activation of latent tuberculosis will also be needed. The evidence from the Guinea-Bissau study suggests that a history of BCG vaccination should not be an obstacle to the diagnosis and treatment of latent tuberculosis.