Association Between Post-COVID-19 Infection and Fibromyalgia: A Controlled Case–Control Study

<b>Background</b>: Persistent musculoskeletal pain has been increasingly reported following COVID-19 infection. However, the association between post-COVID-19 infection and fibromyalgia diagnosed using standardized criteria remains incompletely understood. <b>Objective</b>: This study aimed to investigate the association between post-COVID-19 infection and fibromyalgia diagnosed according to the 2016 American College of Rheumatology (ACR) criteria. <b>Methods</b>: In this case-control study, individuals with post-COVID-19 infection were compared with COVID-19-negative controls. Fibromyalgia was diagnosed using the ACR 2016 criteria. Clinical assessments were performed under standardized conditions. Patients with ongoing symptoms compatible with long COVID were excluded based on clinical evaluation. <b>Results</b>: The prevalence of fibromyalgia was significantly higher in participants with post-COVID-19 infection compared with controls. Individuals in the post-COVID group demonstrated higher odds of meeting ACR 2016 fibromyalgia criteria and exhibited greater symptom burden across clinical measures. These findings indicate a robust association between post-COVID-19 infection and subsequent fibromyalgia diagnosis. <b>Conclusions</b>: Post-COVID-19 infection was associated with an increased likelihood of fibromyalgia diagnosed using standardized criteria. While causality cannot be inferred due to the observational design, the findings highlight the importance of considering fibromyalgia in patients presenting with persistent musculoskeletal pain after COVID-19 and support further longitudinal and mechanistic research. These findings should be interpreted in light of the observational design and potential selection bias inherent to the case-control methodology.