Diagnostic Accuracy of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis in a High-HIV-Prevalence Setting

Abstract

Sputumacid-fastbacilli (AFB) smear microscopy has suboptimal sensitivity but remains the most commonly used laboratory test to diagnose pulmonary tuberculosis (TB). We prospectively evaluated the small membrane filtration (SMF) method that concentrates AFB in a smaller area to facilitate detection to improve the diagnostic performance of microscopy. We enrolled adults with suspicion of pulmonary TB from health facilities in south western Uganda. Clinical history, physical examination, and 3sputum samples were obtained for direct fluorescent AFB smear, SMF, XpertMTB/RIF, and MGIT culture media. Sensitivity and specificity were estimated for SMF, AFB smear, and XpertMTB/RIF, using MGIT as the reference standard. The analysis was stratified according to HIV status. From September 2012 to April 2014, 737 participants were included in the HIV-infected stratum (146[20.5%] were culture positive) and 313 were in the HIV-un infected stratum (85[28%] were culture positive). In HIV-infected patients, the sensitivity of a single SMF was 67.4%(95% confidence interval [CI],59.9% to 74.1%); for AFB, 68.0% (95%CI,60.6%to74.6%); and for XpertMTB/RIF, 91.0%(95%CI, 85.0% to 94.8%). In HIV-un infected patients, the corresponding sensitivities were 72.5%(95%CI,62.1% to 80.9%),80.3%(95%CI,70.8%to87.2%), and 93.5%(95%CI,85.7% to 97.2%). The specificity for all 3 tests in both HIV groups was>96%. In this setting, the SMF method did not improve the diagnostic accuracy of sputum AFB. The XpertMTB/RIF assay performed well in both HIV-infected and-uninfected groups.