Association between influenza infection and subsequent Parkinson’s disease diagnosis: a systematic review and meta-analysis

Introduction As infectious agents may be associated with neurodegenerative diseases, this systematic review and meta-analysis investigated whether prior influenza infection is associated with an increased odds of subsequent Parkinson’s disease (PD) diagnosis.Methods We searched PubMed, Web of Science, and Scopus for observational studies examining influenza infection and later PD diagnosis. Seven studies (comprising eight cohorts) were analyzed using frequentist and Bayesian random-effects meta-analyses. Meta-regression and subgroup analyses were conducted to explore the moderating effect of the time interval between influenza exposure and subsequent PD diagnosis (i.e. exposure window).Results A significant association was observed in both approaches: pooled OR = 1.87 (95% CI: 1.24–2.81) under the frequentist model, and posterior median OR = 1.88 (95% CrI: 1.07–3.36) under the Bayesian model. Meta-regression and subgroup analyses identified the influenza exposure window as a moderator (R2 = 36.6%, p < 0.05), with studies reporting influenza exposure within five years before PD diagnosis showing the strongest associations.Conclusion Our findings support a probable and temporally sensitive association between influenza infection and subsequent PD diagnosis. However, these findings should be interpreted cautiously, given the retrospective and heterogeneous nature of the available data.