Methods: This retrospective cohort study evaluated all patients diagnosed with MAC pulmonary disease at our institution from 2000 to 2012. After identifying patients who suffered a clinical relapse of MAC, we calculated the elapsed time from completion of therapy for the initial infection to the time of clinical relapse. We then regrew these banked isolates, subjected these isolates to PFGE in order to differentiate true relapses versus reinfection, and performed macrolide susceptibility testing on each isolate.
Results: Of the 190 patients who completed anti-MAC therapy, 48 (25%) suffered a clinical relapse. Forty-five pairs of isolates were subjected to PFGE and we found that 25 (56%) of the patients suffered a true relapse and 20 (44%) had a reinfection. The median time between completion of therapy and clinical relapse was significantly lower in the true relapse group compared to the reinfection group (210 days vs. 671 days, p<0.001). The measured convalescent macrolide minimum inhibitory concentrations (MICs) were significantly more likely to decrease in the reinfection group compared to the true relapse group (63% vs 17%, p=0.004).
Conclusion: Our findings suggest that patients with a true relapse of MAC pulmonary disease present earlier than those with reinfection. The routine use of PFGE to aid in the management of clinical relapses of MAC pulmonary disease may be beneficial as those suffering a true relapse are more likely to have increasing macrolide MICs compared to those with reinfection.
C. Qi, None