The diagnosis of tuberculosis: what’s old, what’s new

The approach to the diagnosis of both active tuberculosis and latent infection has changed very little in the past several decades. For active disease, sputum smears with or without chest radiographs to aid in diagnostic accuracy, form the cornerstone of the diagnostic approach in many high-burden countries. These tests usually are supplemented by cultures when resources permit. The diagnosis of latent infection still relies on the use of the tuberculin skin test using purified protein derivative. The current global tuberculosis epidemic, which features large numbers of patients with human immunodeficiency virus infection and increasing rates of multidrug-resistant tuberculosis, makes accurate and rapid diagnosis of tuberculosis more urgent than ever before. Currently available technologies, most involving techniques of DNA amplification, can substantially improve the accuracy of the diagnosis of tuberculosis, although the use of such assays has been sharply limited because of concerns about cost. However, economic analyses suggest that these assays can be cost effective if they lead to sharp reductions in transmission through earlier treatment of infectious cases.