Research Article: Epidemiology of Tuberculosis in a High HIV Prevalence Population Provided with Enhanced Diagnosis of Symptomatic Disease

Date Published: January 2, 2007

Publisher: Public Library of Science

Author(s): Elizabeth L Corbett, Tsitsi Bandason, Yin Bun Cheung, Shungu Munyati, Peter Godfrey-Faussett, Richard Hayes, Gavin Churchyard, Anthony Butterworth, Peter Mason, Mario Raviglione

Abstract: BackgroundDirectly observed treatment short course (DOTS), the global control strategy aimed at controlling tuberculosis (TB) 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. We investigated the epidemiology of prevalent and incident TB in a high HIV prevalence population provided with enhanced primary health care.Methods and FindingsTwenty-two businesses in Harare, Zimbabwe, were provided with free smear- and culture-based investigation of TB symptoms through occupational clinics. Anonymised HIV tests were requested from all employees. After 2 y of follow-up for incident TB, a culture-based survey for undiagnosed prevalent TB was conducted. A total of 6,440 of 7,478 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 (adjusted incidence rate ratio = 18.8; 95% confidence interval [CI] = 10.3 to 34.5: population attributable fraction = 78%), and point prevalence after 2 y was 5.7 and 2.6 per 1,000 population (adjusted odds ratio = 1.7; 95% CI = 0.5 to 6.8: population attributable fraction = 14%). Most patients with prevalent culture-positive TB had subclinical disease when first detected.ConclusionsStrategies based on prompt investigation of TB symptoms, such as DOTS, may be an effective way of controlling prevalent TB in high HIV prevalence populations. This may translate into effective control of TB transmission despite high TB incidence rates and a period of subclinical infectiousness in some patients.

Partial Text: Tuberculosis (TB) disease can result from either rapidly progressive disease following recent infection with Mycobacterium tuberculosis or from reactivation of latent TB infection. Reactivational disease predominates in countries that have achieved good control of transmission, but most disease in endemic countries is due to recently transmitted infection [1]. Accordingly, directly observed treatment short course (DOTS), the TB control strategy of the World Health Organization (WHO), aims to reduce the burden of prevalent smear-positive TB through prompt diagnosis and effective treatment of symptomatic patients with infectious disease [1]. In theory, successfully reducing point prevalence will lead to falling TB incidence rates as TB transmission goes into decline (see Box 1) [1]. DOTS has had notable success in a number of countries with low HIV prevalence, and world-wide, it is considered one of the most cost effective of all health interventions [2].

Participation rates are shown in Figure 1. Baseline characteristics of the 6,440 participants are shown by HIV status in Table 1. HIV prevalence was 19%. HIV-positive workers were more likely to have been treated for TB in the past (11% versus 2%, p = 0.027), to have had household contact with a TB patient (22% versus 15%, p < 0.001), and to be middle aged (p = 0.01). They were also more likely to be current or former smokers and to be manual workers (p < 0.001 for both). Workforce turnover was higher for HIV-positive than HIV-negative workers, with 69% and 78%, respectively, remaining in the workforce at the end of follow-up (p < 0.001). The results of this study suggest that passive case finding and treatment, the cornerstone of global TB control, may still be an effective way to control prevalent TB in high HIV prevalence populations, even when control of TB incidence has been apparently unsuccessful. This has major implications for TB control prospects, as it supports an approach whereby DOTS retains the essential role of controlling TB transmission rates, with the addition of integrated HIV/TB care aimed at providing individual protection from the very high risks of TB morbidity and mortality that are a striking feature of HIV disease in TB endemic areas [4]. The overall point prevalence of smear-positive TB after 2 y of easy access to diagnosis was 1.3 per 1,000 population in this study. This is considerably lower than most other reports of adult and whole-population point prevalence estimates from Africa [5,17–25] and Asia [26–34], and below the burden in Africa [17] in the pre-TB treatment era (Figure 3). Although this may in part reflect a “healthy worker” effect in this study, the high HIV prevalence of 19%, our inclusion of all employees who were on sick-leave during the prevalence survey, and the high TB incidence rates argue against this as the sole effect. Of note, our study population was predominantly male and middle-aged, both of which are strong risk factors for prevalent TB disease in other settings [26–29]. Source: http://doi.org/10.1371/journal.pmed.0040022

 

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