Clinical outcomes in Mycobacterium xenopi versus Mycobacterium avium complex pulmonary disease: A retrospective matched cohort study

Mycobacterium xenopi is associated with the highest mortality among pulmonary nontuberculous mycobacterial (NTM) infections, but whether this is due to the infection or other factors is unclear. There is little information regarding outcomes among patients infected with M. xenopi versus other NTM species. We conducted a retrospective matched cohort study comparing M. xenopi pulmonary disease (Mx-PD) to M. avium complex (MAC)-PD. Patients were matched by sex, age, radiologic subtype, and presence of cavitation. Baseline clinical characteristics, treatment, and outcomes were compared using matched analyses. We identified 70 Mx-PD cases: 29 fibrocavitary-type, 28 nodular-bronchiectatic-type, and 13 unclassifiable-type CT patterns, mean (SD) age 63 (13) years, and 54.3% (n = 38) female. Median follow-up duration was longer in the Mx-PD cohort (1552 days versus 1035 days, p = 0.01). Symptoms, radiologic phenotype, and pulmonary function were similar between groups although the Charlson Comorbidity Index was numerically higher in Mx-PD patients (3.6 versus 3.2, p = 0.08). Rifamycins were used less frequently in Mx-PD (59.5% versus 85.7%, p = 0.02). Although combined clinical and radiologic improvement was similar between the groups, successful treatment was more common with Mx-PD (40.5% versus 16.7%, p = 0.02) owing to superior culture conversion (70.8% versus 33.3%, p = 0.0001). Mortality 24 months after initiation of treatment was numerically but not statistically greater in the Mx-PD cohort (20.4% versus 10.3%, p = 0.32). Among matched Mx-PD and MAC-PD patients, standard anti-mycobacterial treatment was significantly more likely to achieve culture conversion and successful treatment for Mx-PD patients. Mortality among Mx-PD patients was numerically, but not statistically higher, possibly explained by increased comorbidity burden.