False Positive Tuberculosis Cases (Xpert MTB/RIF Assay) Among People Living With HIV Attending Bahati Comprehensive Care Centre Nairobi, Kenya

Author(s): Lucy Obonyo Nyang’au, Evans Amukoye, Stanley Kangethe, Jackson Onyuka


The introduction of GeneXpert MTB/RIF assay has impacted positively in tuberculosis diagnosis, providing a rapid way of identifying tuberculosis patients in high burden, low income countries. However Mycobacterium tuberculosis (MTB) detection in previously treated patients, which may be due to old deoxyribonucleic acid or active disease, still remains a diagnostic dilemma for diagnosis of tuberculosis. A retrospective cohort study was conducted among consenting patients with signs and symptoms of tuberculosis attending Bahati comprehensive care centers. A total of three hundred and forty six patients were sampled and their sputa collected, subsequently laboratory analysis was carried out for detection and culture of Mycobacterium tuberculosis. Seventy seven (22%) sputa had Mycobacterium tuberculosis detected on Xpert MTB/RIF assay sputa from these patients with bacteriologically confirmed pulmonary tuberculosis were subjected to culture on Mycobacterium Growth Indicator Tube (MGIT) media. Detection of Mycobacterium tuberculosis on Xpert MTB/RIF assay with no isolation of growth on culture indicated a false positive tuberculosis diagnosis. Out of 77 isolates subjected for culture a total of 0(0%) and 5(7.5%); P=0.484, isoniazid preventive therapy and non- isoniazid preventive therapy patients had false positive tuberculosis cases, while 0(0%) and 5(25%); P=0.001 new and retreatment patient’s had false positive tuberculosis. Our study concluded that there was no significant association between isoniazid preventive therapy and tuberculosis false positivity but there was significant association between patient treatment status and tuberculosis false positivity. Previously treated tuberculosis patients were significantly associated with false positivity, this call for clinicians to exercise caution when interpreting results from previously treated tuberculosis patients.

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