The use of Genexpert MTB/RIF® compared to microscopy culture and sensitivity for the diagnosis of hand and wrist tuberculosis

Abstract

Purpose:

The global burden of Tuberculosis (TB) is ever increasing; the burden in Sub-Saharan Africa is further compounded by the rising number of Human Immunodeficiency Virus (HIV) infections, poverty and overcrowding. Musculoskeletal TB makes up 1% of all infections with spinal, hip and knee involvement being the commonest manifestations. Hand and wrist TB is a far less frequent presentation but with far reaching and devastating complications as the hand is important for prehension and interaction with the environment. The challenges in making a definitive diagnosis of TB are well established, failure to grow the mycobacterium under laboratory culture media may delay initiation of treatment even in the face of symptomatology suggestive of infection. The purpose of the study was to compare the conventional Microscopy culture and sensitivity method with the newer Genexpert MTB/RIF test looking at the sensitivity and specificity, the turnaround time and to report the number of drug resistant cases. Materials and Methods:

A retrospective review of all hand and wrist TB cases was performed from 01 October 2012 until 31 December 2016. All cases diagnosed with hand and wrist TB were included, demographic data, laboratory results including HIV status, Microscopy culture and sensitivity, Genexpert as well as histology results were collected. The sensitivity, specificity and time taken to diagnosis or results between MC&S and Genexpert were analysed, therefore, resistant strains of TB were also reported.

Results and conclusion:

The overall sensitivity and specificity for Genexpert were 86% (95% CI, 48.7 to 97.4) and 33% (95% CI, 13.8 to 60.9) respectively, the positive predictive value (PPV) was 43% and the negative predictive value (NPV) was 80%. There were eight false-positive Genexpert tests and one false-negative Genexpert test. The mean turnaround time of one Genexpert result was two days, that of Microscopy was five days and that for culture was 21 days. iv

Genexpert and Microscopy had a significantly shorter turnaround time (two and five days, respectively) compared to culture with 21 days. Two cases were rifampicin resistant.

Conclusion:

Genexpert MTB/RIF is a reliable and rapid test to timeously diagnose TB. However, the test needs to be correlated with clinical symptoms. Although culture remains the gold standard, prolonged time to diagnosis may delay commencement of therapy.