Increased Susceptibility to Salmonella Infection in Systemic Lupus Erythematosus Compared with Other Systemic Autoimmune Diseases: Insights from a Retrospective Cohort Study from the Largest Health Care System in Taiwan

Systemic lupus erythematosus (SLE) and other systemic autoimmune rheumatic diseases (SARDs) require long-term immunosuppressive therapy, placing patients at increased risk of infection. <i>Salmonella</i> species are particularly concerning due to their invasiveness and potential link to autoimmune activation, notably in SLE. This study aimed to compare the risk of culture-confirmed <i>Salmonella</i> infection between SLE and other SARDs, based on data from the Chang Gung Research Database between 2005 and 2020. After propensity score matching, 3537 patients per group were analyzed. Patients with SLE had a higher incidence of <i>Salmonella</i> infection compared with those with other SARDs (0.54 vs. 0.17 per 1000 person-years), with a significantly greater cumulative incidence (log-rank <i>p</i> < 0.01). The adjusted hazard ratio (HR) for <i>Salmonella</i> infection in SLE was 2.47 (95% confidence interval (CI): 0.95-6.38), and the competing risk model confirmed a significant association (sub-distribution HR 2.58, 95% CI: 1.06-6.29, <i>p</i> = 0.04). Among SLE patients, lymphopenia was the only independent predictor of <i>Salmonella</i> infection (adjusted HR 3.98, 95% CI: 1.83-8.68, <i>p</i> < 0.001). Bloodstream infections were most common (70%), and serogroup D was the predominant strain (80%). These results suggest patients with SLE face higher <i>Salmonella</i> risk than other SARDs, especially those with lymphopenia, underscoring the need for targeted surveillance and preventive strategies.