# Trimethoprim-sulfamethoxazole and the risk of early severe infection in elderly-onset myeloperoxidase-antineutrophil cytoplasmic antibody-associated vasculitis

## TL;DR

This study found that using trimethoprim-sulfamethoxazole may lower the risk of severe infections in elderly patients with a specific type of vasculitis.

## Contribution

The study identifies trimethoprim-sulfamethoxazole as a potential prophylactic for reducing early severe infections in elderly-onset MPO-AAV patients.

## Key findings

- Severe infections occurred in 34% of elderly MPO-AAV patients.
- Trimethoprim-sulfamethoxazole use was significantly associated with reduced infection risk.
- The protective effect of trimethoprim-sulfamethoxazole remained significant after adjusting for sex.

## Abstract

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) has improved survival outcomes with advancements in immunosuppressive therapies; however, the increased incidence of infections remains a significant concern. Reports on infection risk factors other than age are limited, especially in older adults with AAV who are at a higher risk.

We aimed to identify the risk factors for early-phase infection during treatment initiation in older adults (aged ≥ 75 years) with myeloperoxidase (MPO)-ANCA-positive AAV (MPO-AAV). This was a single-center, retrospective observational study that included 50 patients who were classified as having microscopic polyangiitis. Severe infections were defined as those requiring hospitalization within six months of treatment initiation.

Severe infections occurred in 17 (34%) patients. No statistically significant associations were observed between disease incidence and either combined immunosuppressive therapy or organ-specific lesions. However, trimethoprim-sulfamethoxazole (TMP-SMX) was significantly associated with a reduced risk of infection. This association remained statistically significant after adjustment for sex (hazard ratio, 0.23; 95% CI, 0.08–0.64; P < 0.01).

In older adults with MPO-AAV, TMP-SMX use was associated with a reduced risk of early severe infection. Although limited by the observational nature of the study, these findings suggest a potential role for TMP-SMX prophylaxis in high-risk elderly populations.

Not applicable.

The online version contains supplementary material available at 10.1186/s12882-025-04695-y.