Clinical characteristics and therapeutic dilemmas in nocardiosis: Insights from a case series

Nocardiosis often requires prolonged antimicrobial therapy, and trimethoprim-sulfamethoxazole (TMP-SMX) is considered the cornerstone of treatment. However, TMP-SMX-related adverse events frequently complicate long-term therapy, and real-world data regarding treatment continuity and outcomes remain limited.

We conducted a retrospective observational study of patients with Nocardia species isolated from clinical specimens at a tertiary-care academic hospital in Japan between January 2015 and April 2025. Clinical characteristics, antimicrobial therapy, adverse events, and outcomes were reviewed.

Eleven cases were enrolled, with a median age of 65 years. The cohort comprised seven patients with severe nocardiosis (disseminated disease, brain abscess, and pneumonia in transplant recipients) and four patients with mild nocardiosis (cutaneous infection and pneumonia). Nine patients received TMP-SMX as part of the initial regimen, of whom seven required modification of therapy within 1 day to 3 months because of adverse events. Following modification of TMP-SMX, patients were treated with alternative regimens, including fluoroquinolone-and minocycline-based therapies, as well as β-lactam-containing combinations. Importantly, no cases of treatment failure or death were observed, and no relapses were identified during the available follow-up period, even among patients with those clinically complex diseases.

Although TMP-SMX is the first-line therapy for nocardiosis, the majority of our patients did not tolerate the drug. Nevertheless, favorable outcomes were observed with alternative regimens, even in patients with clinically complex disease, suggesting that alternative regimens may be reasonable options when TMP-SMX is not tolerated.