Comparative Sensitivity of Smear Microscopy for Acid Fast Bacilli versus Gene Xpert MTB/RIF Assay on Endobronchial Washings of the Sputum Smear Negative/Sputum Scarce Patients with Suspected Pulmonary Tuberculosis Keeping Culture as Gold Standard

Abstract

Background: Tuberculosis (TB) is the world's tenth most common cause of death, and it continues to be a serious global health problem, generating considerable morbidity and mortality. According to the World Health Organization (WHO) Global Tuberculosis Report 2020, there were an estimated 10 million new tuberculosis cases and 1.4 million tuberculosis deaths globally in 2019. TB incidence and mortality rates have decreased since the WHO end TB Strategy was adopted in 2014; nonetheless, the rate of decline has been far slower than predicted, highlighting the need for better, more focused implementation of this strategy. Objectives: To determine the comparative sensitivity of smear microscopy (SM) for acid fast bacilli (AFB) versus Gene Xpert MTB/RIF assay on endobronchial washings of the Sputum Smear Negative/Sputum scarce patients with suspected Pulmonary tuberculosis (PTB) keeping culture as gold standard. Methodology: This Cross-sectional validational study was carried out in the Department of Pulmonology, Ayub Teaching Hospital Abbottabad, Pakistan from 28th March to 28th September 2022. All patients of any gender having age 20 to 75 years with TB who were sputum smear negative or had scarce sputum were included. Patients who were already diagnosed as PTB and those who were already on anti tuberculous treatment were excluded. Results: Mean age of the patients was 47.02±14.65 years ranging from 20 to 75 years with 44(50.6%) males and 43(49.4%) females. In comparative sensitivity of Gene Xpert with respect to culture as gold standard the sensitivity of Gene Xpert was 93.24% while its specificity was 84.62% with positive predicted value (PPV) of 97.18%, negative predicted value (NPV) of 68.75% and accuracy of 91.95%. In comparative sensitivity of AFB SM with respect to culture as gold standard, the sensitivity of SM was 74.32% and specificity was 53.85%, PPV was 90.16%, NPV was 26.92% and the accuracy was 71.26%. Conclusion: Gene Xpert is more sensitive than SM to detect mycobacterium TB and rifampicin resistance. Gene Xpert can be utilized for earlier detection of rifampicin resistant TB cases on the endobronchial washings while waiting for detailed culture results in suspected PTB cases having either sputum negative or sputum scarce disease. Keywords: Comparative sensitivity, Smear microscopy, Gene Xpert, Endobronchial washings, Sputum smear