Relapse versus reinfection of mycobacterium avium complex pulmonary disease: Patient characteristics and macrolide susceptibility

Rationale: Clinical recurrence of Mycobacterium avium complex (MAC) pulmonary disease occurs in 10 to 40% of patients treated for this disease process. Episodes of clinical recurrence may represent true relapse from the same MAC strain or reinfection with a new strain. Objectives: The purpose of this study was to investigate the clinical implications of separating patients into these two groups. Methods: This retrospective study evaluated patients with a clinical recurrence of MAC pulmonary disease at our institution from 2000 to 2012. Isolates were genotyped using pulsed-field gel electrophoresis to differentiate relapse versus reinfection. Change in macrolide susceptibility was also analyzed. Measurements and Main Results: In our cohort, 25% of patients suffered a clinical recurrence. Of the 46 included patients, 25 (54%) suffered a true relapse and 21 (46%) had a reinfection. Median time between completion of therapy and clinical recurrence was significantly lower in the relapse group compared with the reinfection group (210 d vs. 671 d;P = 0.004).The measured convalescent macrolide minimum inhibitory concentrations were significantly more likely to increase in the relapse group compared with the reinfection group (80 vs. 33%; P = 0.002). No differences in clinical outcomes were observed between the two groups at conclusion of the study. Conclusions: Our findings suggest that patients with true relapse of MAC pulmonary disease present earlier than those with reinfection. Routine use of pulsed-field gel electrophoresis in the management of clinical recurrences may be beneficial, as those suffering a relapse are more likely to have increasing macrolide minimum inhibitory concentrations than those with reinfection.