When I was an intern, tuberculosis was fairly easy to treat but difficult to diagnose. Now the situation has changed dramatically. A new test promises to speed the diagnosis while treating TB has become harder, because many people are infected with drug-resistant organisms or have immune systems too weak to fight the infection.

Tuberculosis can infect many sites in the body but most commonly affects the lungs. With current diagnostic tests, the diagnosis of pulmonary TB requires a multi-step process: getting a coughed-up specimen from the person suspected of having the disease, growing a culture from the specimen in a laboratory, and waiting three to four weeks to identify Mycobacterium tuberculosis, the organism that causes TB.

The new diagnostic test, recently evaluated in Peru, can diagnose TB within one week and simultaneously determines whether the organism is resistant to multiple drugs.

In the United States, tuberculosis is reasonably well-controlled - the 14,000 new cases reported in 2005 is a remarkable decline from the 84,000 new cases in 1953. Many of the new cases occur in people with damaged immune systems due to HIV infection. Though everyone entering the U.S. as a refugee or immigrant is screened for TB, new cases are more common among foreign-born people. The disease tends to affect poor people living in crowded conditions.

Despite the progress made in the U.S. to control TB, the disease remains an enormous health problem around the world. In 2000 8.3 million new cases were reported, and an estimated 1.7 million people die of tuberculosis each year. TB is rampant in sub-Saharan Africa, India, and China. Between 10 and 30 percent of cases in these regions are associated with HIV infection. 

The long wait in making the diagnosis with presently used tests not only means a delay in starting treatment but a longer period when the infected person can spread the disease to others. In addition, infections with strains of M. tuberculosis that are resistant to two or more of the drugs used to treat the infection are becoming more common.

A person with resistant TB may be treated for months before doctors realize that the infection is due to a multiple-drug-resistant strain. The delay in treating these patients with the proper drug allows their disease to worsen and permits further spread of drug-resistant infections in the community.

The new test holds promise for earlier initiation of treatment and the use of effective drugs in those with resistant strains. Both of these measures will help prevent spread of the infection to others.