Slide 103 Epidemiologic Basis of Tuberculosis Control
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In Tanzania, the number of reported sputum smear-positive cases increased more than 3-fold in just 25 years despite the presence of an exemplary tuberculosis control program.

The cases are shown here on a logartithmic scale to show that the increase in sputum smear-negative cases has been steeper than in sputum smear-positive cases, but relapse frequency has gone in exact parallel, thus HIV infection does not seem to have resulted in a deterioration of the quality of the chosen treatment regimen.

In contrast to Europe in the previous example, the prevalence of tuberculous infection in the the age segments at highest risk of HIV infection is large, and as shown earlier estimated to be about 50% in the critical age groups. Thus each HIV infection has a 50% probability to coincide with a tuberculous infection. This must necessarily lead to a large number of HIV infected persons developing tuberculosis through reactivation of a latent tuberculous infection.

Furthermore, as half of the population in the critical age groups has no tuberculous infection, they remain susceptible to become infected through the excess of infectious cases of tuberculosis. Some of them will be already infected with HIV and have little defenses against direct progression to overt clinical tuberculosis, further adding sources of infection to the community. Others, free of HIV infection, may also become infected with M. tuberculosis and become at risk of future development of tuberculosis.

The situation is likely to be similar in numerous other sub-Saharan African countries, but the true impact of HIV on the epidemiologic situation of tuberculosis remains hidden in many, because both diagnostic capabilities and surveillance are underdeveloped. A tuberculin skin test survey in Kenya suggests that the risk of tuberculous infection has already increased despite the time required for such a change to become measurable.

Unless the HIV epidemic comes under control, tuberculosis will apparently be out of control in many such countries.

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Last update: September 10, 2010