In August 2005, the World Health Organization (WHO) declared the tuberculosis (TB) epidemic in Africa to be a regional, if not a global, emergency. The cross-sectional survey conducted by Robin Wood et al. in sub-Saharan Africa aimed to determine the effectiveness of the Directly Observed Treatment, Short-course (DOTS) run in this area, also affected by the HIV epidemic, to control TB transmission in the population. In contrast to the last paper studied (Corbett et al.) the authors found that the DOTS program was insufficient in controlling the dissemination of TB in a high HIV prevalence community. This was found to be predominately due to the fact that Mycobacterium tuberculosis infection tended to present itself atypically in HIV infected individuals, remaining asymptomatic or sub clinical in co-infected persons. This finding led the researchers to conclude that the passive case finding strategy of the DOTS program, which relies on self-presentation of TB symptoms, is inadequate in quelling the spread of tuberculosis.
The study to determine the extent of the burden of undiagnosed TB in the presence of a functional DOTS program, within the confines of a burgeoning HIV epidemic, was conducted using a cross-sectional survey of randomly sampled individuals in a geographically demarcated area. The participants of the study gave written informed consent and the study received approval from the Research Ethics Committee of the University of Cape Town. The venue of the study was a single public-sector primary care clinic which obtained sputum samples from participants that were examined for the presence of acid-fast bacilli (AFB). A second sputum smear positive for AFB or culture of Mycobacterium tuberculosis in requisite growth indicator tubes confirmed diagnosis of TB. Smear negative pulmonary tuberculosis (PTB) was defined by the inability to identify AFB in the sputum smear but was confirmed by two positive cultures with identical spoligotype patterns which ruled out the possibility of sample cross contamination.
The study found that symptoms were not a useful screen for PTB, being absent in 67% of those previously undiagnosed. Of those undiagnosed individuals found to be infected with TB, 75% were HIV positive. It was found to be a characteristic of HIV/TB co-infection that TB symptoms were often absent or unrecognized. As such, the DOTS program instituted in the area was unable to effectively diagnose the majority of individuals with TB, thereby being unable to control the transmission and infectiousness of the bacterium. For prior to initiation of antibiotic therapy, TB infection in an individual remains highly communicable, despite the lack of obvious symptoms. The study found that 63% of community PTB adult cases remained undiagnosed, as was evident through the cross sectional prevalence study. This reveals that the majority of the community burden of TB was unrecognized by the treatment services available through the DOTS program. The majority of these individuals were HIV positive.
As the mean duration of infectiousness is the main determinant of the epidemic spread of TB, the investigators concluded that it is necessary that more active case finding be implemented by the DOTS program if it is to be successful in controlling the tuberculosis epidemic in Africa. Particularly in HIV positive individuals, a more proactive approach to TB screening is needed in order to control the spread of the bacteria. Passive self-presentation of TB symptoms, which the DOTS program relies upon, will not be effective in controlling the transmission of the mycobacterium agent in HIV endemic areas and more intensive strategies are required if the epidemic spread of TB is to be slowed.
