PCR colorimetric dot-blot assay and clinical pretest probability for diagnosis of Pulmonary Tuberculosis in Smear-Negative patients

• Published in: BMC public health Vol. 7; no. 1; p. 356
• Main Authors: Scherer, Luciene Cardoso, Sperhacke, Rosa Dea, Jarczewski, Carla, Cafrune, Patrícia I, Minghelli, Simone, Ribeiro, Marta Osório, Mello, Fernanda CQ, Ruffino-Netto, Antonio, Rossetti, Maria LR, Kritski, Afrânio L
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 20.12.2007; BioMed Central; BMC
• Subjects: Adult; Brazil; Care and treatment; Causes of; Colorimetry; Cough; Developing Countries; Diagnosis; DNA, Bacterial - analysis; Health aspects; Humans; Methods; Molecular Probe Techniques; Mycobacterium tuberculosis; Mycobacterium tuberculosis - genetics; Mycobacterium tuberculosis - isolation & purification; Nucleotide Mapping; Polymerase chain reaction; Polymerase Chain Reaction - methods; Probability; Pulmonary tuberculosis; Sensitivity and Specificity; Sputum - microbiology; Tuberculosis, Pulmonary - diagnosis; Tuberculosis, Pulmonary - epidemiology; Tuberculosis, Pulmonary - microbiology; Brazil
• ISSN: 1471-2458; 1471-2458
• DOI: 10.1186/1471-2458-7-356

Smear-negative pulmonary tuberculosis (SNPTB) accounts for 30% of Pulmonary Tuberculosis (PTB) cases reported annually in developing nations. Polymerase chain reaction (PCR) may provide an alternative for the rapid detection of Mycobacterium tuberculosis (MTB); however little data are available regarding the clinical utility of PCR in SNPTB, in a setting with a high burden of TB/HIV co-infection. To evaluate the performance of the PCR dot-blot in parallel with pretest probability (Clinical Suspicion) in patients suspected of having SNPTB, a prospective study of 213 individuals with clinical and radiological suspicion of SNPTB was carried out from May 2003 to May 2004, in a TB/HIV reference hospital. Respiratory specialists estimated the pretest probability of active disease into high, intermediate, low categories. Expectorated sputum was examined by direct microscopy (Ziehl-Neelsen staining), culture (Lowenstein Jensen) and PCR dot-blot. Gold standard was based on culture positivity combined with the clinical definition of PTB. In smear-negative and HIV subjects, active PTB was diagnosed in 28.4% (43/151) and 42.2% (19/45), respectively. In the high, intermediate and low pretest probability categories active PTB was diagnosed in 67.4% (31/46), 24% (6/25), 7.5% (6/80), respectively. PCR had sensitivity of 65% (CI 95%: 50%-78%) and specificity of 83% (CI 95%: 75%-89%). There was no difference in the sensitivity of PCR in relation to HIV status. PCR sensitivity and specificity among non-previously TB treated and those treated in the past were, respectively: 69%, 43%, 85% and 80%. The high pretest probability, when used as a diagnostic test, had sensitivity of 72% (CI 95%:57%-84%) and specificity of 86% (CI 95%:78%-92%). Using the PCR dot-blot in parallel with high pretest probability as a diagnostic test, sensitivity, specificity, positive and negative predictive values were: 90%, 71%, 75%, and 88%, respectively. Among non-previously TB treated and HIV subjects, this approach had sensitivity, specificity, positive and negative predictive values of 91%, 79%, 81%, 90%, and 90%, 65%, 72%, 88%, respectively. PCR dot-blot associated with a high clinical suspicion may provide an important contribution to the diagnosis of SNPTB mainly in patients that have not been previously treated attended at a TB/HIV reference hospital.