TB/ HIV
Directly observed treatment short course (DOTS), the global control strategy aimed at controlling tuberculosis transmission through prompt diagnosis of symptomatic smear-positive disease, has failed to prevent rising tuberculosis incidence rates in Africa brought about by the HIV epidemic. However, rising incidence does not necessarily imply failure to control tuberculosis transmission, which is primarily driven by prevalent infectious disease. Corbett and colleagues investigated the epidemiology of prevalent and incident tuberculosis in a high HIV prevalence population provided with enhanced primary health care. Twenty-two businesses in Harare, Zimbabwe, were provided with free smear- and culture-based investigation of tuberculosis symptoms through occupational clinics. Anonymous HIV tests were requested from all employees. After two years of follow-up for incident tuberculosis, a culture-based survey for undiagnosed prevalent tuberculosis was conducted. A total of 6440 of 7478 eligible employees participated. HIV prevalence was 19%. For HIV-positive and -negative participants, the incidence of culture-positive tuberculosis was 25.3 and 1.3 per 1,000 person-years, respectively (RR 18.8, 95% CI 10.3-34.5: population attributable fraction = 78%), and point prevalence after 2 years was 5.7 and 2.6 per 1,000 population (OR 1.7; 95% CI 0.5-6.8: population attributable fraction = 14%). Most patients with prevalent culture-positive tuberculosis had sub-clinical disease when first detected. The authors conclude that strategies based on prompt investigation of tuberculosis symptoms, such as DOTS, may be an effective way of controlling prevalent tuberculosis in high HIV prevalence populations. This may translate into effective control of tuberculosis transmission despite high tuberculosis incidence rates and a period of sub-clinical infectiousness in some patients.
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