Chickenpox and Risk of Stroke: A Self-controlled Case Series Analysis

Background. There is good evidence that respiratory and other infections that cause systemic inflammation can trigger strokes; however, the role of specific infections is unclear. Case reports have highlighted chickenpox as a pos-sible risk factor for arterial ischemic stroke, particularly in children, but rigorous studies are needed to determine and quantify any increased risk. Methods. We used anonymized electronic health records totaling>100 million person-years of observation from 4 UK primary care databases to identify individuals who had documented clinical chickenpox and a stroke or transient ischemic attack (TIA). Self-controlled case series methods were used to quantify any increased risk of first stroke or TIA in the 0–6 and 7–12 months following chickenpox compared to other observed time periods. We ana-lyzed data within each database, and performed meta-analyses to obtain summary age-adjusted incidence ratios (IRs) separately for adults and children. Results. Five hundred sixty eligible individuals (including 60 children) were identified who experienced chick-enpox and a stroke or TIA during follow-up. Among children, there was a 4-fold increased risk of stroke in the 0–6 months after chickenpox (summary IR = 4.07; 95 % confidence interval [CI], 1.96–8.45; I2 = 0%). Among adults, there was a less marked increased risk with moderate between-database heterogeneity (random-effects summary IR = 2.13; 95 % CI, 1.05–4.36; I2 = 51%). There was no significant increased risk of stroke in the 7–12 months after chickenpox in children or adults, nor was there evidence of increased risk of TIA in either time period. Conclusions. Our study provides new evidence that children who experience chickenpox are at increased risk of stroke in the subsequent 6 months