title: Evaluation of the Xpert® MTB/Rif test, microscopic observation drug susceptibility test and nitrate reductase assay, for rapid and accurate diagnosis of smear-negative tuberculosis in HIV patients.
abstract: Diagnosis of smear-negative tuberculosis (TB), which is frequently seen in HIV-infected patients, is a challenge without conventional culture methods. Since 2007, the WHO (World Health Organization) has endorsed new or improved tests for increased and rapid diagnosis of TB. This study was undertaken in an effort to evaluate the accuracy of two rapid culture methods: the Microscopic Observation Drug Susceptibility assay (MODS) and Nitrate Reductase Assay (NRA), and the molecular based test Xpert® MTB/Rif (Xpert), for diagnosis of smear-negative TB in HIV patients using the mycobacteria growth indicator tube (MGIT) in the BACTEC(TM) MGIT(TM) 960 system as the reference test. 430 smear-negative patients with presumptive TB were enrolled in a cross-sectional study at a tertiary care facility in Uganda. Their sputum was tested on MODS, NRA, Xpert and MGIT. Of the 430 patients, 373 had complete results to compute test accuracy. Mycobacterium tuberculosis (MTB) was detected in 43 patients by MGIT. The sensitivity and specificity were 24.4% and 98.1% for MODS, 41.5% and 92% for NRA, 48.8% and 95.1% for Xpert, respectively. The low sensitivity of the tests implies that additional diagnostics such as chest X-ray and conventional liquid culture methods might still be needed to detect TB in smear-negative HIV patients. The high specificity of the tests is useful to confirm TB in HIV patients with symptoms suggestive of TB.
authors.affiliation: Department of Medical Microbiology, Makerere University, College of Health Sciences, Kampala, Uganda; Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.
authors.forename: Simon
authors.initials: S
authors.lastname: Walusimbi
authors.affiliation: Department of Medical Microbiology, Makerere University, College of Health Sciences, Kampala, Uganda.
authors.forename: Freddie
authors.initials: F
authors.lastname: Bwanga
authors.affiliation: Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.
authors.forename: Ayesha De
authors.initials: AD
authors.lastname: Costa
authors.affiliation: Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden; Department of Diagnostics and Vaccinology, Swedish Institute for Communicable Disease Control, Solna, Sweden. Electronic address: melles.haile@smi.se.
authors.forename: Melles
authors.initials: M
authors.lastname: Haile
authors.affiliation: Department of Diagnostics and Vaccinology, Swedish Institute for Communicable Disease Control, Solna, Sweden; Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institute, Stockholm, Sweden.
authors.forename: Sven
authors.initials: S
authors.lastname: Hoffner
authors.affiliation: Department of Medical Microbiology, Makerere University, College of Health Sciences, Kampala, Uganda.
authors.forename: Moses
authors.initials: M
authors.lastname: Joloba
keywords: HIV and TB; MGIT; MODS; NRA; Smear negative TB; Xpert