There are limited studies on the association between systemic autoimmune rheumatic diseases (SARDs) and leptospirosis. Therefore, this study aims to identify the effects of leptospirosis on the risks of developing SARDs with a nationwide retrospective cohort study. Patients with leptospirosis who did not have a diagnosis of SARDs before the index date were enrolled from the Taiwan National Health Insurance Research Database between 2000 and 2010, as the leptospirosis cohort. For each patient with leptospirosis, one control without a history of leptospirosis and SARDs was randomly selected (non-leptospirosis cohort). Cox proportional hazards regression models were used to analyze the risk of SARDs according to sex, age, and comorbidities. Among the 23 million people in the cohort, 3,393 patients with leptospirosis (68.91% men, mean age 52.65 years) and 33,930 controls were followed for 18,778 and 232,999 person-years, respectively. The incidence of SARDs was higher in the leptospirosis cohort than in the non-leptospirosis cohort (1.38 vs 0.33 per 1000 person-years), with a hazard ratio (HR) of 4.42 (95% confidence interval [CI] = 2.82–6.92). The risk of developing SARDs was highest for leptospirosis patients aged ≥65 years (HR = 2.81% CI = 1.07–7.36) compared with patients aged ≤39 years. Patients with leptospirosis have a 4.42-fold higher risk of SARDs than that in the general population. Further research is warranted to investigate the mechanism underlying this association.
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