Monotherapy: Key cause of macrolide-resistant Mycobacterium avium complex disease.

Background: Macrolide-resistant Mycobacterium avium complex (MAC) disease is very difficult to cure. Macrolide-resistance emerges in patients and is largely preventable by appropriate screening and treatment practices.

Methods: Patients with macrolide-resistant MAC isolates between March 2019 and March 2022 were retrieved from the mycobacteriology reference laboratory database at Radboudumc, Nijmegen, the Netherlands. Clinical consultation reports were extracted from the database to assess the cause of macrolide resistance.

Results: Sixteen patients with macrolide-resistant MAC disease were included, from a total of 815 patients with MAC isolates (2%); Macrolide monotherapy in bronchiectasis or CF was the most frequent cause of development of macrolide-resistance MAC disease (n = 8; 50%). Short (n = 3; mean duration 9 months, range 6-12) or guideline non-compliant (n = 2) treatment regimens and patient non-adherence (n = 2) were other key causes of macrolide-resistance.

Conclusions: Macrolide monotherapy after inappropriate screening is the most frequent cause of macrolide-resistant Mycobacterium avium complex disease in the Netherlands. Educational efforts are needed to prevent this.