Recent transmission of tuberculosis in a cohort of HIV-1-infected female sex workers in Nairobi, Kenya

Abstract

Objectives: To describe the epidemiological and clinical characteristics of HIV-related tuberculosis in a female cohort, and to investigate the relative importance of recently transmitted infection and reactivation in the pathogenesis of adult HIV-related tuberculosis.

Design: Members of an established cohort of female sex workers in Nairobi were enrolled in a prospective study. Women were followed up regularly and seen on demand when sick.

Methods: Between October 1989 and September 1992 we followed 587 HIV-infected and 132 HIV-seronegative women. Standard protocols were used to investigate common presentations. Cases of tuberculosis were identified clinically or by culture. All available Mycobacterium tuberculosis strains underwent DNA fingerprint analysis.

Results: Forty-nine incident and four recurrent episodes of tuberculosis were seen in HIV-infected women; no disease was seen in seronegative sex workers (P = 0.0003). The overall incidence rate of tuberculosis was 34.5 per 1000 person-years amongst HIV-infected participants. In purified protein derivative (PPD) skin test-positive women the rate was 66.7 per 1000 person-years versus 18.1 per 1000 person-years in PPD-negative women. Twenty incident cases (41%) were clinically compatible with primary disease. DNA fingerprint analysis of strains from 32 incident cases identified two clusters comprising two and nine patients; allowing for index cases, 10 patients (28%) may have had recently transmitted disease. Three out of 10 (30%) patients who were initially PPD skin test-negative became PPD-positive. Taken together, 26 incident cases (53%) may have been recently infected. DNA fingerprint analysis also identified two (50%) of the four recurrent tuberculosis episodes as reinfection.

Conclusions: Substantial recent transmission of tuberculosis appears to be occurring in Nairobi amongst HIV-infected sex workers. It may be incorrect to assume in other regions of high tuberculosis transmission that active HIV-related tuberculosis usually represents reactivation of latent infection.

PIP: A 3-year (1989-92) prospective study of 587 HIV-positive and 132 HIV-negative commercial sex workers in Nairobi, Kenya, revealed substantial recent transmission of tuberculosis in the HIV-infected group. The cohort was enrolled at a community clinic that provides counseling, sexually transmitted disease services, and free condoms. In HIV-positive women, 49 incident and 4 recurrent episodes of tuberculosis were diagnosed during the study period; there were no tuberculosis cases among HIV-negative women. The overall incidence rate of tuberculosis was 34.5/1000 person-years among HIV-positive women. 20 incident cases (41%) met the clinical case definition of primary disease. DNA fingerprint analysis of strains from 32 incident cases suggested 10 women (28%) may have had recently transmitted disease. 3 of 10 women who were initially purified protein derivative (PPD) skin test-negative became PPD-positive. Clinical presentation, tuberculin skin testing, and strain clustering data all independently suggested that substantial Mycobacterium tuberculosis transmission was occurring in HIV-infected prostitutes during the study period. As many as 26 (53%) of the 49 patients with incident disease may have recently acquired tuberculosis and DNA fingerprint analysis identified 2 (50%) of the 4 recurrent tuberculosis episodes as reinfection. These findings challenge the assumption that tuberculosis in HIV-infected individuals represents reactivation of latent endogenous infection.