MEASUREMENT AND DETERMINANTS OF TUBERCULOSIS OUTCOME IN KARONGA DISTRICT, MALAWI

Evaluation of disease outcome is central to the assessment of tubercul osis (TB) control programmes. In the study reported in this article we examined the factors influencing the measurement of outcome, survival rates during and after treatment, smear conversion rates, and relapse rates for patients diagnosed with TB in a rural area of Malawi betwee n 1986 and mid-1994. Patients with less certain diagnoses of TB were m ore likely to die than those with confirmed TB, both among those who w ere seropositive and those who were seronegative to human immunodefici ency virus (HIV), The mortality rate among smear-positive patients wit h a separate culture-positive specimen was half that of patients with no such diagnostic confirmation. Patients not registered by the Minist ry of Health had much higher mortality and default rates than did regi stered patients. Among smear-positive patients, HIV serostatus was the most important influence on mortality both during and after treatment (crude hazard ratios (95% confidence intervals) = 5.6 (3.0-10) and 7. 7 (3.4-17), resp,), but HIV serostatus did not influence smear convers ion rates. The initial degree of smear positivity influenced smear con version rates, but not mortality rates. No significant predictors of r elapse were identified. Unless considerable care is taken to include a ll TB patients, and to exclude nontuberculous patients, recorded TB ou tcome statistics are difficult to interpret and may be misleading. In populations with high rates of HIV infection, TB target cure rates of 85% are unrealistic. When new interventions are assessed it cannot be assumed that factors which influence the smear conversion rate will al so influence the mortality rate.