Additional biomarkers are needed to guide the start of Mycobacterium avium pulmonary illness (Mav-PD) treatment. TTP (time to positive sputum culture detection) may have prognostic and monitoring implications. To examine if TTP is linked to infection severity and early treatment response in Mav-PD patients. During 2015-2019, researchers conducted a retrospective cohort analysis of patients who had two positive sputum cultures for M. avium, an ‘index’ sputum M. avium isolates, a CT scan within 6 months, and no treatment for ≥6 months before the index sputum. The researchers calculated TTP from when the specimen arrived in the laboratory to when the culture-positive was confirmed. TTP was analyzed using Mann-Whitney U, Spearman’s Correlation Coefficient, and Wilcoxon signed-rank tests to see if it was associated with markers of infection severity (Mav-PD, bronchiectasis, cavitary disease, treatment initiation by 3 and 6 months, AFB smear). They looked into a TTP threshold that could detect M. avium illness. There were 125 patients in all, with a mean (SD) age of 68.5 (12.5) years and 65% meeting disease criteria. TTP was 12 days on average (IQR 10-15; range 6-44). TTP and the grade of the AFB smear were adversely linked (ρ -0.58, p<0.001). TTP was linked to NTM illness (p=0.03), AFB smear positivity (p<0.001), and three (p=0.01) and six (p=0.03) month therapy beginning. A threshold TTP of ≤10 days was associated with Mav-PD (80.6% vs 58.4%; ð (95%CI) 22.1 (5.6-38.6)%,p=0.02), AFB smear positivity (83.3% vs 20.2%, ð (95%CI) 63.1(48.3-77.9)%, p<0.001), treatment by three (38.9% vs 13.5%; ð (95%CI) 25.4 (8.0-42.8)%, p=0.003) and six (47.2% vs 19.1%; ð (95%CI) 28.1 (9.9-46.4)%,p=0.003) months. After three and six months of treatment, the median (IQR) change in TTP was +8 (1-undefined; p<0.001) and +7 (0-undefined; p=0.001) days respectively. TTP is linked to bacterial burden and infection severity, and treatment response. A threshold of ≤10 days could help predict substantial Mav-PD. TTP should be investigated more because it is an easily available biomarker.