JULY 2001 — Tuberculosis (TB) continues to be one of the most important global public health threats. The World Health Organization (WHO) estimates that the incidence of TB increased by 5 percent between 1997 and 1999, from 8 million to 8.4 million new cases. African countries severely affected by the HIV epidemic experienced a 20 percent increase in the incidence of TB; this rise is largely responsible for the TB increase globally.

TB was considered on the brink of elimination in the developed world until the late 1980s, when new HIV-related TB cases and multi-drug-resistant tuberculosis (MDR-TB) surfaced. In developing countries, however, TB has remained an important public health problem, exacerbated in the last decade by poverty, demographic changes and the rapid spread of HIV. Most TB patients in high HIV-prevalent countries are HIV-infected.

The relationship between TB and HIV has been recognized since the early days of the HIV epidemic. Today HIV is known to be an important risk factor, contributing to the development of active TB from latent TB infection. A person co-infected with TB (positive PPD skin test) and HIV faces a five percent to 16 percent annual risk of developing active TB disease. HIV also makes individuals with a recent TB infection more likely to progress rapidly to active TB disease. WHO estimates that more than 10 million people worldwide live co-infected with TB and HIV, more than two-thirds of whom are in sub-Saharan Africa.

HIV is not only fueling the TB epidemic but is also making TB control more challenging. The increase in new TB cases is likely to contribute to the overcrowding of health care facilities, draining human and financial resources from already under-funded health services. This overcrowding could prevent new infectious TB patients from seeking medical care, thereby contributing to lower case detection rates and risking further spread of TB into the community. Overcrowded health facilities will also increase the workload of health care workers, which may result in inferior case detection and treatment monitoring.

Some data suggest that HIV-related stigma may prevent TB patients from seeking medical care, resulting in delayed diagnoses and further TB transmission. Many TB patients have died during the course of treatment. Malawi, for instance, has reported more than 20 percent mortality rate among TB patients on treatment. Finally, TB continues to be the leading cause of mortality among AIDS patients. Autopsy studies have shown that more than 30 percent of deaths in people with AIDS were due to TB.

The emergence of MDR-TB constitutes another challenge to TB control. MDR-TB is expensive to manage and generally associated with a high fatality rate. In the last decade, outbreaks of MDR-TB among HIV-infected patients were reported in the United States and Europe, and were associated with high-case fatality rates. Most of these outbreaks occurred in nosocomial settings such as prisons and hospitals. While the U.S. and Western Europe appear to have contained it, MDR-TB remains a major public health problem in Eastern Europe, especially in the republics of the former Soviet Union. In Africa, with the exception of Côte d'Ivoire and Mozambique, MDR-TB is not yet a public health problem. The situation in Asia is unclear but, given the burden of TB in the region, MDR-TB might become a more severe problem there.

TB is an important disease to target in areas with high HIV infection rates because it is one of the rare infectious diseases that is fueled by the HIV epidemic but does not remain confined to HIV-infected individuals. Because TB is also one of the first opportunistic infections to appear in HIV-infected individuals — perhaps first suggesting the presence of HIV — addressing TB offers the opportunity for early HIV intervention. Controlling it in high HIV-prevalent countries will require that the Directly Observed Therapy, Short-course (DOTS) strategy be supplemented by other interventions, such as active TB case finding and treatment of latent TB infection among HIV-infected individuals.