Resurgence of tuberculosis and the impact of HIV infection.

Tuberculosis is increasing in many countries. In some areas the major influences on tuberculosis trends are the traditional ones: poverty, failures in the treatment system, and immigration. In others, and increasingly, the HIV epidemic is having a huge impact. HIV infection increases the risk of tuberculosis approximately 7-fold, though this may vary with the stage of the HIV epidemic, the prevalence of tuberculosis, and the age groups considered. Dually-infected individuals develop tuberculous disease at a rate of 5-10% per year. HIV also increases the risk of disease following recent infection, which makes a major contribution to the tuberculosis burden in some settings. HIV-infected individuals, may transmit Mycobacterium tuberculosis less than do HIV-negative individuals, but the extra cases will add to the transmission overall, and evidence of HIV-attributable increases in the annual risk of infection is beginning to be seen.