Prompt diagnosis and treatment by DOTS resulted in the control of prevalent tuberculosis in a high HIV prevalence Zimbabwean population

The DOTS approach to TB treatment - directly observed treatment, short course - can reduce the prevalence of TB in a population where HIV infection is endemic, British and Zimbabwean researchers report in the January edition of PLoS Medicine.

In resource-poor countries with an escalating HIV/AIDS problem, tuberculosis (TB) places a considerable burden on fragile public health systems trying to cope with malaria and HIV. TB is harder to diagnose and progresses faster in people living with AIDS (PLWA) in whom the disease is more likely to be fatal if undiagnosed or left untreated. TB occurs earlier in the course of HIV infection than other opportunistic infections, and it is the only major AIDS-related opportunistic infection that poses a risk to HIV-negative people.

TB control can be achieved by diagnosis and treatment. In this regard, DOTS (Directly Observed Treatment, Short-course) has become a cornerstone for controlling TB in many countries. It combines prompt and appropriate diagnosis of TB and registration of the patient detected, followed by standardised treatment, a sustainable supply of high quality anti-TB drugs for all patients under treatment, individual patient outcome evaluation to ensure cure, and cohort evaluation to monitor overall program performance.

Between 1995 and 2003, more than 17.1 million patients were treated under the DOTS strategy. By the end of 2003, 182 countries were implementing the DOTS strategy and 77% of the world's population was living in regions where DOTS was in place. DOTS programs reported 1.8 million new TB cases through lab testing in 2003, a case detection rate of 45%, and the average success rate for DOTS treatment was 82%.

The main criticism of DOTS is that several well-conducted randomised control trials with or without other components have shown no benefit from it. Furthermore, DOTS has failed to prevent rising TB incidence rates in Africa brought about by the HIV epidemic. However, a new study by British and Zimbabwean investigators provides some evidence that DOTS might be effective in controlling prevalent TB despite rising TB incidence rates in high HIV prevalence populations.

The study was carried out between September 2001 and July 2002 as part of a larger trial in which the use of company clinics and voucher-based voluntary counselling and testing for HIV (VCT) were being compared for providing VCT in the work place. The study took place within 22 small and medium-sized enterprises (SMEs) in Harare, Zimbabwe, a country with a high HIV prevalence in adults. Companies were randomly allocated to either of the two VCT strategies.

Employees were asked to provide blood for HIV testing and subjected to a baseline questionnaire which captured information about a history of previous TB treatment and household contacts. VCT was provided to workers wishing to know their HIV status. A total of 6,440 workers, of whom 19 % were HIV-positive, were followed up for two years with the aim of detecting TB in the population.

During follow-up, patients presenting with a cough for three weeks or more were tested for TB by sputum smears and cultures. Chest X-rays were taken if symptoms persisted after treatment with broad-spectrum antibiotics. HIV patients received cotrimoxazole and isoniazid prophylaxis. Antiretroviral drugs were not available at the time. Active treatment was excluded before starting isoniazid.

One hundred and six cases of TB were seen, and HIV-positive workers by comparison with HIV-negative work-mates were more likely to experience TB, to have been a household contact of a TB patient, and to be middle-aged. The incidence of culture-positive TB was significantly higher in HIV-positive than HIV-negative workers (25.3 versus 1.3 per 1,000 person years of follow-up).

At the end of the two-year follow-up, 4,668 workers were checked for the presence of undiagnosed TB disease and cultures were carried out to find out how many of these people had infectious TB. Twenty seven workers had active TB giving a work force prevalence of 5.8 per 1,000 for all TB, and 3.2 and 1.3 per 1,000 for culture-positive and smear-positive TB, respectively. Some of these workers carried no symptoms and were detected only upon screening by culture. HIV infection, smoking, and older age were significant risk factors for prevalent TB.

The authors concluded that the systems set up within the trial for close follow up and testing for TB disease were effective in reducing the overall proportion of the population with infectious TB in a high HIV prevalence population. This probably means that the spread of TB infection to others was also reduced. This is the target goal of TB control programs.

The authors also make specific recommendations. First, the added value of routine periodic screening for asymptomatic TB among people living with HIV/AIDS needs to be determined. Second, the impact of antiretroviral drugs on the sub-clinical period of infectiousness among HIV-positive TB patients must be investigated.

This study by Corbett and colleagues need to be replicated in more African countries with an escalating HIV-1 problem since it suggests that DOTS might, after all, if well-implemented with rigorous case-finding and treatment, prove capable of reducing TB incidence in high HIV prevalence settings in the long term.