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Background: Our aim was to describe the annual prevalence of herpes simplex virus (HSV) reactivation in relation to solar ultraviolet (UV) radiation and antiviral drug use in the Swedish adult population.

Methods: The study comprised 2879 anti-HSV-1 immunoglobulin (Ig) G positive subjects from five different cohorts who had donated serum from 1988 to 2010. The sera were analyzed for anti-HSV IgM using enzyme-linked immunosorbent assay. Associations between the presence of anti-HSV IgM antibodies, the apolipoprotein E ε4 allele and the serum sampling year were assessed by logistic regression. Seasonality of anti-HSV IgM was evaluated in a UV radiation model. Data of antiviral drugs for the entire Swedish population were compiled from two different nationwide databases: the Swedish Prescribed Drug Register and the Swedish Association of the Pharmaceutical Industry.

Results: Cross-sectional and longitudinal analyses indicated that the prevalence of anti-HSV IgM antibodies declined between 1988 and 2010 (odds ratio [OR] = 0.912, p <.001), while the total annual use of antiviral drugs in Sweden gradually increased from 1984 to 2017. Higher UV radiation was associated with higher prevalence of anti-HSV IgM antibodies (OR = 1.071, p =.043).

Conclusion: The declining time trend of HSV reactivation in a Swedish cohort coincides with a steady increase of antiviral drug use in the Swedish general population.