Dissertation (MMED Microbiology and Immunology)Non tuberculous mycobacterium are increasingly being recognized as human pathogens, causing morbidity and mortality to the society. Both non tuberculous mycobacterium and Mycobacterium tuberculosis are acid fast bacilli. Patients with non tuberculous mycobacterium pulmonary infection may present with clinical features similar to pulmonary tuberculosis infection. Because both non tuberculous and mycobacterium tuberculosis are acid fast bacilli, they cannot be distinguished by smear microscope, a routine diagnostic method in resource limited settings like Tanzania. As a result patients with non tuberculous mycobacterium may be prescribed anti-tuberculosis drugs. The study aimed to determine the prevalence, predictors and antimicrobial susceptibility pattern of non tuberculous mycobacterium among patients with smear positive results. Between October 2020 to March 2021 this cross-sectional analytical study design consented and recruited 140 patients with positive sputum smear microscopy results for acid fast bacilli. Patients provided sputum sample for Mycobacterial culture on solid Lowenstein Jensen media. The GenoType CM/AS (Hain Life science, Nehren, Germany) kit detected species from cultures isolates. Antimicrobial susceptibility testing was performed using proportion method on Lowenstein Jensen media. Normally distributed continuous data were summarized as mean with standard deviation. While Fisher’s exact test compared proportion, binary logistic regression model estimated the odds for detecting non tuberculous mycobacterium. A p value of ˂0.05 was considered significance. Out of 140 patients with acid fast bacilli sputum smear positive, 6(4.29%) had non tubercuulous mycobacterium infection and were identified as Mycobacterium avium (n=4) and Mycobacterium kansasii (n = 2). All 6 non tuberculous mycobacterium species were resistant to isoniazid, rifampcin and ethambutol but were sensitive to kanamycin, amikacin and ofloxacin. In adjusted binary regression model, patients with history of previous pulmonary tuberculosis infection were 7.76 times likely to have non tuberculous mycobacterium compared to those who had no exposure to Mycobacterium tuberculosis infection (p = 0.038). Non tuberculous mycobacterium is prevalent among patients with sputum smear positive for acid fast bacilli suggesting continual screening. Previous history of pulmonary tuberculosis infection was an independent predictor of non tuberculous mycobacterium infection. All non tuberculous mycobacterium were susceptible to aminoglycosides (kanamycin and amikacin) and fluoroquinolones such as ofloxacin.