HIV and tuberculosis: a deadly human syndemic

Abstract

A syndemic is defined as the convergence of two or more diseases that act synergistically to magnify the burden of disease. The intersection and syndemic interaction between the human immunodeficiency virus (HIV) and tuberculosis (TB) epidemics have had deadly consequences around the world. Without adequate control of the TB-HIV syndemic, the long-term TB elimination target set for 2050 will not be reached. There is an urgent need for additional resources and novel approaches for the diagnosis, treatment, and prevention of both HIV and TB. Moreover, multidisciplinary approaches that consider HIV and TB together, rather than as separate problems and diseases, will be necessary to prevent further worsening of the HIV-TB syndemic. This review examines current knowledge of the state and impact of the HIV-TB syndemic and reviews the epidemiological, clinical, cellular, and molecular interactions between HIV and TB.

Fig. 1.

Higher HIV prevalence rates are associated with higher TB incidence rates. We used data from 132 countries from the UNAIDS/WHO 2008 report on the global AIDS epidemic for HIV prevalence (250) and from the WHO 2009 report on global tuberculosis control for TB incidence (263) and generated a scatter plot showing a positive linear correlation. The Pearson correlation coefficient (r) was 0.799, with a (two-tailed) P value of <0.01 using SPSS statistical software.

Fig. 2.

HIV-associated TB contributes disproportionately to TB-related deaths. (Data are from WHO Global Tuberculosis Control: a Short Update to the 2009 Report [262].) Although HIV-associated TB accounted for 15% of all incident TB, it contributed to 29% of deaths among incident TB cases in 2008. The estimated case-fatality rate of incident TB was more than 2-fold higher for people infected with HIV (37%) than for those without HIV (16%).

Fig. 3.

Estimated excess TB cases attributed to the worsening HIV epidemic in the United States from 1985 to 1992. (Reprinted from reference .)

Fig. 4.

As the CD4 cell count declines, the frequency of cavitation in pulmonary TB decreases. Data were pooled from 12 studies (6, 19, 34, 66, 71, 105, 143, 144, 159, 199, 208, 210) that examined the frequency of lung cavitation associated with CD4 counts in patients coinfected with HIV and pulmonary TB. Patients whose CD4 count was above 200 cells/μl had a 4-fold-higher odds of having cavitary pulmonary TB than those with CD4 counts below 200 cells/μl (odds ratio, 4.44; 95% CI, 3.36, 5.88).

Fig. 5.

TB incidence rates decrease with recovery of CD4 cell counts during antiretroviral therapy. TB incidence is defined as incident TB cases per 100 person-years, with 95% confidence intervals shown. The blue line represents baseline TB incidence (0.7 cases/100 person-years) in adults without HIV in a comparable neighboring community. (Adapted from reference with permission of the publisher.)