Recurrent TB: relapse or reinfection? The effect of HIV in a general population cohort in Malawi

To estimate rates of recurrent tuberculosis due to reinfection and relapse, by HIV status, in a general population.

Long-term cohort study in Karonga district, rural Malawi.

All tuberculosis patients with culture-proven disease in Karonga district were followed up after treatment. HIV testing was offered and all Mycobacterium tuberculosis isolates were fingerprinted using IS6110 RFLP. Fingerprints from initial and recurrent disease episodes were compared to distinguish relapse and reinfection: a second episode was considered a relapse if the fingerprint was identical or differed by only 1-4 bands and was the first occurrence of that pattern in the population. Rates of and risk factors for recurrence, reinfection disease, and relapse were estimated using survival analysis and Poisson regression.

Five hundred and eighty-four culture-positive episodes of tuberculosis were diagnosed and treatment was completed during 1995-2003 in patients with known HIV status; 53 culture-positive recurrences occurred by May 2005. Paired fingerprints were available for 39 of these. Reinfections accounted for 1/16 recurrences in HIV-negative and 12/23 in HIV-positive individuals. Rates of relapse were similar in HIV-positive and HIV-negative individuals. Using multiple imputation to allow for missing fingerprint information, the rate of reinfection disease in HIV-positive individuals was 2.2/100 person-years, and in HIV-negative individuals 0.4/100 person-years.

HIV increases the rate of recurrent tuberculosis in this setting by increasing the rate of reinfection disease, not relapse.