Increased risk of rheumatoid arthritis among patients with Mycoplasma pneumonia: A nationwide population-based cohort study in Taiwan

Objective: An association between Mycoplasma pneumonia (MP) and rheumatoid arthritis (RA) had been reported in animal studies for decades. However, clinical evidence for this association is lacking. Therefore, this study aimed to provide epidemiologic evidence to clarify the relationship between MP and development of RA. Methods: This 13-year nationwide, population-based, retrospective cohort study analyzed the risk of RA in a cohort of MP patients. We cross linked and compared the database of those with catastrophic illnesses to make sure the diagnoses of RA are correctly labeled. We selected 116,053 hospitalized patients diagnosed with MP between 2000 and 2012 from the Taiwan National Health Insurance Research Database and 464,212 matched controls at a 1:4 ratio by age, gender, and index year, in relation to the risk of developing RA. The follow-up period referred to the initial diagnosis of MP until the date of RA diagnosis, censoring of RA, or 31st December 2013. The Cox proportional hazard model was used to analyze the association between MP and incidence of RA among patients with different potential risks. Results: The adjusted hazard ratio (HR) for incidental RA in the MP group was 1.37 (95% confidence interval CI = 0.87–2.16), compared to non-MP controls. Stratified analysis revealed that the adjusted HR was 3.05 (95% CI = 1.16–7.99, p = 0.02) in a subgroup of patients over the age of 65.The adjusted HR of RA for the MP group among aged ≦19 years and ≥ 65 years was 3.19 (95% CI = 1.04.9.76) and 4.14 (95% CI = 1.27,13.4) within the first 2 years of follow-up. Conclusion: This cohort study demonstrated that patients with MP had a higher risk of developing RA, especially in the first 2 years, in those aged younger than 19 and over 65.