Association of Scrub Typhus With the Risk of Autoimmune Diseases: A Population-Based Cohort Study

Infection plays a major role in the development of autoimmune diseases. In this study, we investigated the relationship between scrub typhus and systemic autoimmune diseases. We enrolled 6,928 hospitalized patients with scrub typhus between 2000 and 2012 from the Taiwan National Health Insurance Research Database, and we compared them with 27,712 selected inpatients who had never been diagnosed with scrub typhus (1:4 ratio, matched by age, sex, and index year) in relation to the risk of developing autoimmune diseases. Cox proportional hazards regression analysis was used to analyze the risk of autoimmune diseases by sex, age, and comorbidities, with hazard ratios and 95% confidence intervals. The adjusted hazard ratio for autoimmune diseases for the scrub typhus group was 2.4 (95% confidence interval: 1.66, 3.48, P < 0.0001) compared with the control group. Subgroup analysis showed that women aged <40 years had a significant higher risk of autoimmune diseases. The risk was significantly higher within 3 years after scrub typhus infection. In conclusion, a higher risk of autoimmune diseases was found among the scrub typhus group, especially for female patients, those aged <40 years, and within the first 3 years after getting scrub typhus.