Diagnosis of active pulmonary tuberculosis using the xpert MTB/RIF assay in smear negative tuberculosis suspects at Kenyatta National hospital and Mbagathi district hospital.
Abstract
Background: Pulmonary tuberculosis (PTB) is a major global health problem and currently it
stands as the second leading cause of mortality from a single infectious disease worldwide
according to the WHO world TB report 2012. Over the past century, diagnosis of PTB has relied
almost exclusively on smear microscopy which has been shown to have a low sensitivity
especially in patients co-infected with HIV. Novel diagnostic methods, such as the recently
developed Xpert MTB/RIF assay are bound to be essential tools in the global fight against TB.
Objectives: In this study, we sought to determine the yield of this novel assay in the
microbiological diagnosis of PTB in patients suspected to have PTB who are sputum smear
negative.
Design: It was a cross sectional descriptive study
Setting: The Kenyatta National Hospital (KNH) and Mbagathi District Hospital (MDH).
Methods: Files of prospective patients seen at the Tb clinics of both hospitals and the Tb wards
in MDH were perused. Those which met the inclusion criteria were recruited with consent into
the study and the study questionnaire administered. Spot sputum samples from each patient
which were of proper quality were tested for active mycobacterium tuberculosis and rifampicin
resistance using the Xpert MTB/RIF assay. Data from the study questionnaire and results of the
assay were entered and analyzed using SSPS version 17.0 software. Measured outcomes
included the proportion of active PTB in smear negative PTB suspects; the prevalence of
rifampicin resistance in this group and the association between the Xpert MTB/RIF assay result
and patients presenting symptoms.
Results: A total of 179 sputum samples were run from 179 eligible participants. The Xpert
MTB/RIF assay yield was high at 19% (95%CI 13.5-25.5) with a 0% rifampicin resistance rate.
Presence of night sweats on its own, or both night sweats and weight loss were weakly
associated with Xpert MTB/RIF assay positivity (OR 10.1; 95%CI 1.3-76.7, p=0.007) and (OR
7.1; 95% CI 2.1-24.3, p<0.001) respectively.
Conclusion: The additional yield of the Xpert MTB/RIF assay in patients who are sputum smear
negative PTB suspects in our study is 19% which when taken in the context of a 34% notified
smear negative rate in Kenya, is high. This has important public health implications wherein
patients who can transmit Tb are not being identified by smear microscopy.
Publisher
University of Nairobi