Cost-effectiveness in the diagnosis of tuberculosis: choices in developing countries

Tuberculosis remains one of the major causes of global death from a single infectious agent. This situation is worsened by the HIV/AIDS pandemic because one-third of HIV/AIDS patients are co-infected with Mycobacterium tuberculosis. Failure to control the spread of tuberculosis is largely due to our inability to detect and treat all infectious cases of pulmonary tuberculosis in a timely manner, allowing continued M. tuberculosis transmission within communities. Diagnosis of tuberculosis can be made using indirect and direct methods. The indirect tests, such as interferon-gamma release assays, provide a new diagnostic method for M. tuberculosis infection, but do not discriminate between infection and active disease. The most common direct method for diagnosing TB worldwide is sputum smear microscopy (developed more than 100 years ago), where bacteria are observed in sputum samples examined under a microscope. In countries with more developed laboratory capacities, cases of tuberculosis may also be diagnosed using culture methods (the current gold standard) or, increasingly, using rapid molecular tests. In this review, we discuss the traditional methods for the diagnosis of tuberculosis. We also discuss other inexpensive assays that can be used to detect the presence of M. tuberculosis.