The impact the HIV pandemic would have upon TB control first began to be appreciated in the early 90's. TB transmission had become very rare in countries such as the US, but a growing number of documented de novo infections were occurring, often in clusters, among people exposed to AIDS patients with TB.
Then in 1991, there was a much-publicised outbreak of multi-drug resistant TB (MDR-TB) in New York and public health officials feared an epidemic of MDR-TB was possible.
Salvage therapy of MDR-TB is extremely challenging: drug sensitivity testing takes time, the duration of effective treatment is much longer, second line drugs tend to be less well tolerated and, in the early 90's, some of these medications were in very short supply. With limited options on the horizon (TB drug development having fizzled out decades earlier), a strategy was needed to avert a public health nightmare.
The strategy chosen was Directly Observed Treatment - Short course (DOTS) developed by the World Health Organization to improve adherence (and response) to TB treatment, and prevent the development of resistance. To ensure that every dose is taken correctly and at the right time, the treatment is 'directly observed' by treatment supporters (health workers, family members etc) assigned to monitor the patient.
Key principles for the success of DOTS programmes include:
- Government commitment to sustained anti-TB efforts (including education and training of prescribers and treatment supporters)
- Information systems for monitoring and reporting
- Adequate testing and facilities for case detection
- Regular and uninterrupted drug supplies, and, of course
- Observed treatment
Patients with active smear positive TB are directly treated a two-month induction course usually containing four anti-TB drugs (rifampicin (RF) and isoniazid (INH) and two other medications). The short course of induction therapy is followed by a less intense treatment continuation phase, usually with two drugs. Current WHO treatment guidelines for national TB programmes recommend using either a continuation phase of four months with the two most powerful TB drugs, RF/INH, or six months of INH and ethambutol (E).
If the key principles of DOTS are observed, WHO estimated that approximately 85% of TB patients could recover. At this cure rate, it was projected that the global burden of TB could be halved in ten years if at least 70% of active smear-positive cases, i.e. the most infectious patients, were detected and managed by DOTS.
The approach appeared to work well enough in low incidence settings like the States and Western Europe - probably helped along by the subsequent introduction of antiretroviral therapy for HIV.
However, DOTS based programmes are labour-intensive and effective implementation has proved a challenge in many resource-limited, high-prevalence areas where HIV still goes largely untreated. Twenty-three high-incidence countries account for approximately 80% of all new cases. In many of these, TB incidence continues to rise.
A growing number of people working in HIV are now questioning whether DOTS is always the best approach to TB management.
"My concern about TB DOTS is that even in countries with fairly functional programs, such as Botswana, the TB numbers have continued to climb. Ditto in the mining industry in SA," said HATIP advisor, Dr. Francois Venter and clinical director of the Esselen Street Project in Hillbrow (Johannesburg). "At a national meeting, one of our most senior government figures, on seeing our TB numbers, said we 'should go back to the drawing board' as our programs were ' clearly not working'. If TB DOTS is as wonderful as WHO bravely proclaims, it's not showing. My sense is that DOTS would've worked pre-HIV, but in high prevalence countries, it's not enough."
In Chennai India, Dr Vijay Anthony Prabhu reports mixed results with DOTS. "We are experiencing serious problems with DOTS which from clinical experience seems to be inadequate. Problems of treatment failure, especially drug resistance or inadequate duration of continuation phase treatment are problems for ordinary people. What more when the patient is HIV positive."