Clinical diagnosis of smear-negative pulmonary tuberculosis in low-income countries: the current evidence.

Sputum smear examination for acid-fast bacilli (AFB) can diagnose up to 50-60% of cases of pulmonary tuberculosis in well-equipped laboratories. In low-income countries, poor access to high-quality microscopy services contributes to even lower rates of AFB detection. Furthermore, in countries with high prevalence of both pulmonary tuberculosis and HIV infection, the detection rate is even lower owing to the paucibacillary nature of pulmonary tuberculosis in patients with HIV infection. In the absence of positive sputum smears for AFB, at primary care level, most cases of pulmonary tuberculosis are diagnosed on the basis of clinical and radiological indicators. This review aims to evaluate various criteria, algorithms, scoring systems, and clinical indicators used in low-income countries in the diagnosis of pulmonary tuberculosis in people with suspected tuberculosis but repeated negative sputum smears. Several algorithms and clinical scoring systems based on local epidemiology have been developed to predict smear-negative tuberculosis. Few of these have been validated within the local context. However, in areas where smear-negative tuberculosis poses a major public-health problem, these algorithms may be useful to national tuberculosis programmes by providing a starting point for development their own context-specific diagnostic guidelines.