Accuracy of Clinical Signs in the Diagnosis of Pulmonary Tuberculosis: Comparison of Three Reference Standards Using Data from a Tertiary Care Centre in Rwanda

Abstract

Objective: To determine the prevalence of TB, and the diagnostic sensitivity and specificity of major disease characteristics in a tertiary hospital setting in Rwanda, relative to three reference standards. Study Design and Setting: A prospective study was conducted in which 300 consecutive patients with cough of at least 2-weeks duration were evaluated at a tertiary healthcare facility. We compared the estimates of TB prevalence and the diagnostic accuracy of fever, haemoptysis, sputum smear microscopy, radiological signs, and HIV infection as generated by a latent class analysis (LCA) with those given by culture and by a composite reference standard (CRS), which relied on bacteriological confirmation and/or cavities. Results: LCA estimated the prevalence of TB at 44%. The most sensitive characteristics were fever (90%) and HIV infection (86%), but both lacked specificity. The most specific characteristics were microscopy (99%), X-Ray cavities (97%) and apical infiltrates (93%). When culture was taken as a reference standard, the prevalence was 38%; for the CRS, it was 45%. For both, the diagnostic sensitivity and specificity were comparable to those obtained with LCA. Conclusion: Three reference standards produced comparable diagnostic sensitivities and specificities using major symptoms and signs of pulmonary TB; only LCA allowed estimating the diagnostic characteristics of culture. Both LCA and CRS estimated the probability of disease higher than culture alone.