GeneXpert® assay; and its performance for the diagnosis of HIV-associated tuberculosis: Is scale-up worth it?

Abstract

Background: Synergistic Tuberculosis (TB) and human immunodeficiency virus (HIV) co-infections are responsible for epidemics in several nations and have established themselves as a tremendous health challenge to these nations in terms of patient point of care and economic burden on health care organizations. TB is the fundamental driver of HIV-related mortality around the world. Co-infection with these two pathogens results in an accelerated course for the two illnesses and raises complex challenges in diagnosis and therapy. TB and HIV both work in synergy to accelerate the deterioration of the immunological defense mechanisms often leading to death. This present study was designed to evaluate the performance of GeneXpert assay for the detection of Mycobacterium tuberculosis among HIV positive and negative TB patients. Methods and materials: The present prospective cross-sectional study was conducted in the Mycobacteriology laboratory, Allama Iqbal Medical College, Lahore, Pakistan from 2011–2017. A total of 3784 (HIV-ve n = 3568, HIV +ve n = 216) sputum samples were collected with complete history from patients strongly suspected for pulmonary TB (PTB) patients. HIV status was evaluated by PCR (Quantitative) and then referred for Flow-cytometry and GeneXpert assay for MTB Results: Out of a total of n = 3784 PTB, the prevalence of HIV was 5.7% (n = 216/3784). Of 216 HIV positive, 15.7% (n = 34) were also co-infected with TB. The sensitivity of the ZN smear and GeneXpert assay was considerably reduced among HIV and TB co-infected patients. The sensitivity and specificity of ZN smear was 63.7%, and 100% among HIV negative compared to 23.5% and 100% among HIV positive individuals respectively. Whereas sensitivity and specificity of the GeneXpert were found to be 94.5% and 100% for HIV negative individuals as compared to the 76.4%, and 100% respectively among the HIV positive patients. Furthermore, in the case of smear-negative samples, GeneXpert assay showed noticeable sensitivity and specificity 85.8%, 100% and 69.2%, 100%, respectively for HIV negative and positive patients. Conclusion: The GeneXpert assay showed an overall better sensitivity compared to the ZN smear for the diagnosis of TB, the sensitivity was much less in TB patients co-infected with HIV, compared to the HIV negative patients.