The incidence of tuberculosis (TB) is similar between individuals infected with HIV-1 and HIV-2, according to a study conducted in the Gambia, and published in the September 24th edition of AIDS. The investigators also established that mortality rates due to TB were similar between individuals infected with HIV-1 and HIV-2 and that mortality was highest amongst individuals with a CD4 cell count below 200 cells/mm3.
Although HIV-1 and HIV-2 share similar modes of transmission, the risk of transmission, rate of disease progression, speed of CD4 cell loss, and mortality are lower in individuals infected with HIV-2. These differences are partly explained by the lower viral load seen in HIV-2 infected individuals compared to those infected with HIV-1.
TB is the most commonly diagnosed AIDS-defining illness and most frequent cause of death amongst HIV-positive individuals in sub-Saharan Africa. Little is known about the incidence of TB and subsequent mortality in HIV-2 infected patients compared with patients infected with HIV-1. HIV-2 is widespread in West Africa from Sierra Leone to Nigeria.
Accordingly, investigators measured the incidence rate of TB and mortality in HIV-1 and HIV-2 infected individuals attending an HIV clinic in The Gambia. The investigators related both TB incidence and mortality to CD4 cell count for both HIV-1 and HIV-2.
The medical records of 2012 individuals infected with HIV-1 or HIV-2 were retrospectively analysed. TB was diagnosed in a total of 368 patients. There were no significant differences in the time after HIV diagnosis that TB was diagnosed between HIV-1 and HIV-2 infected individuals, or in the site of TB infection.
In total 47.8% of patients had a CD4 cell count below 200 cells/mm3 (49.1% of TB cases in HIV-1 infected patients and 45.1% of TB cases in HIV-2 infected patients, no significant statistical difference, p = 0.8).
The incidence rate of TB was 3.8/100 person years for HIV-1 infected patients and 2.8/100 person years for individuals infected with HIV-2. Although the crude incidence rate for TB was lower for HIV-2 infected patients, this difference disappeared after adjusting for baseline CD4 cell count (p = 0.3).
As would be expected, HIV incidence was highest for individuals with a CD4 cell count below 200 cells/mm3 and lowest for patients whose CD4 cell count was above 500 cells/mm3. There was no difference in any CD4 cell strata for the incidence of TB between HIV-1 and HIV-2 (p = 0.2).
A total of 119 individuals in whom TB was diagnosed died. The overall mortality rate was 43.5/100 person years, and the median survival time post-TB diagnosis was 8.9 months. Both mortality and median survival were comparable between HIV-1 and HIV-2 infected patients.
There was no difference in the median CD4 cell counts of HIV-1 and HIV-2 infected individuals collected within three months of their death (both 50 cells/mm3). Mortality was significantly higher for both HIV-1 and HIV-2 infected patients with TB than for patients with both types of HIV who did not have TB. For HIV-1 infected patients this increased risk of death was most marked for individuals with a CD4 cell count above 500 cells/mm3. For HIV-2 infected patients the increased risk of death amongst TB patients was evident across all CD4 cell strata.
“The incidence of TB was similar among HIV-1 and HIV-2-infected patients in a clinic-based cohort in the Gambia, adjusted for CD4 cell counts. Once TB is diagnosed, survival for HIV-1 and HIV-2-infected patients is equally poor,” conclude the investigators.
Van der Sande, MAB et al. Incidence of tuberculosis and survival after its diagnosis in patients infected with HIV-1 and HIV-2. AIDS 18: 1933-1941, 2004.