Supplementary Material for: Herpes Simplex Virus Infection and Risk of Alzheimer's Disease: A Systematic Review and Meta-Analysis

Introduction: The relationship between Herpes Simplex Virus (HSV) infection and the risk of Alzheimer's Disease (AD) remains unclear.
Methods: A systematic review and meta-analysis were conducted to investigate this potential association. Observational studies were sourced from PubMed, Embase, Web of Science, and the Cochrane Library up to July 31, 2024. The analysis utilized the generic inverse variance method with a random effects model. Effect sizes were calculated as odds ratios (OR) or hazard ratios (HR) with corresponding 95% confidence intervals (CI).
Results: A total of 26 original studies, encompassing 1,213,193 participants, were included in the meta-analysis. The findings indicated a 32% higher likelihood of AD in individuals with HSV infection in case-control studies (OR = 1.32; 95% CI: 1.12, 1.55; I2 = 22.7%) and a 20% increased risk in cohort studies (HR = 1.20; 95% CI: 1.10, 1.31; I2 = 11.0%). Specifically, HSV-1 infection was associated with 46% higher odds of AD (OR = 1.46; 95% CI: 1.14, 1.86; I2 = 3.1%).
Conclusion: This meta-analysis demonstrates an association between HSV infection and increased risk of AD, particularly for HSV-1. Given the high global prevalence of HSV-1 and the heterogeneity of existing evidence, these findings should be regarded as hypothesis-generating, underscoring the need for rigorous, biomarker-informed studies to clarify causality and identify susceptible subgroups.