Accurate diagnosis of Nontuberculous mycobacterial pulmonary disease (NTM-PD) depends on the quality of sputum specimens. While assessing sputum purulence may enhance diagnostic accuracy in NTM-PD, its utility has yet to be fully established.

This single-center retrospective study included 183 patients with NTM-PD. Sputum specimen quality was assessed using the Miller and Jones classification, and the association between the grade of sputum purulence and NTM culture positivity was evaluated. Additionally, we investigated whether specimens with lower purulence grades retained diagnostic value.

Of 469 sputum specimens evaluated, 252 (53.7 %) were NTM culture positive. Purulent specimens graded as P1, P2, and P3 showed significantly higher culture positivity rates compared to non-purulent specimens and were strongly associated with positive NTM culture (OR 4.58; 95 % CI, 2.961–7.086; p < 0.001). Culture positivity rates were 65.3 % for P1, 65.7 % for P2, and 65.9 % for P3 specimens, versus 36.4 % for M1 and 36.8 % for M2 specimens. Notably, approximately one-third of the lower-purulence (M1, M2) specimens still yielded positive cultures, indicating that they retain diagnostic value.

Sputum purulence as assessed using the Miller and Jones classification provides valuable diagnostic information for NTM-PD. While purulent sputum (P1–P3) is strongly associated with positive culture and smear results, specimens with lower purulence grades (M1 and M2) also retain diagnostic value. These findings support the practicable use of sputum purulence assessment to enhance diagnostic yield in clinical settings.

Nontuberculous mycobacterial pulmonary disease

Mycobacterium avium complex

Miller and Jones classification

Sputum specimen quality

© 2025 Japanese Society of Chemotherapy, Japanese Association for Infectious Diseases, and Japanese Society for Infection Prevention and Control. Published by Elsevier Ltd.