Analysis of clinical characteristics and prognosis of sulfonamide-resistant Nocardia species infections: a retrospective study

Trimethoprim-sulfamethoxazole (TMP-SMZ) resistance occurs frequently in multiple Nocardia species. However, there remains a paucity of research on TMP-SMZ-resistant Nocardia species infections. This study aims to characterize the clinical features of TMP-SMZ-resistant Nocardia infections, providing references for clinical diagnosis and management. We retrospectively reviewed clinical-radiological-microbiological data of 36 patients with TMP-SMZ-resistant Nocardia spp. infections admitted to Peking Union Medical College Hospital from January 2014 to April 2024. Patients were stratified into two groups based on immunosuppression status and the clinical characteristics were compared. Data from 75 patients in the sulfonamide-sensitive group were collected, and comparisons of bacterial species, clinical characteristics, and prognosis were performed between the sulfonamide-sensitive group and the sulfonamide-resistant group. A total of 36 sulfonamide-resistant patients was enrolled in this study, with a mean age of (62.0 ± 14.0) years. Pulmonary infection was documented in 35 of 36 patients (97.2%). Nocardia farcinica was the most commonly isolated pathogen. Bronchiectasis was identified radiologically in 23 patients (63.9%). Patients in the immunosuppressed group presented with more severe clinical symptoms and radiological manifestations; however, the between-group differences did not achieve statistical significance after Bonferroni correction. Compared with the non-immunosuppressed group, the immunosuppressed group had a higher prevalence of concurrent opportunistic infections, such as cytomegalovirus viremia (46.2% vs. 0%, p = 0.029). Nocardia farcinica was the most frequently isolated species in both the sulfonamide-resistant and sulfonamide-sensitive groups, with a numerically higher proportion in the sulfonamide-resistant group (41.7% vs. 30.7%) while the difference was not statistically significant. Nocardia farcinica was the predominant TMP-SMZ-resistant species in this cohort. No significant differences in clinical symptoms or radiological manifestations were observed between immunosuppressed and non-immunosuppressed patients after correction for multiple comparisons. In suspected TMP-SMZ-resistant Nocardia infection, molecular diagnostics may enable timely species identification and species-level AST, potentially supporting treatment optimization.