Risk of stroke with antivenom usage after venomous snakebite in Taiwan: a population-based cohort study

Summary Background and purpose Stroke is a rare complication of snakebites, but may lead to serious sequelae. We aimed to explore the relationship between venomous snakebite and the risk for acute stroke, in a nationwide population-based cohort study. Methods This retrospective cohort study used claims data between 1 January 2000 and 31 December 2012, from the Taiwan National Health Insurance Research Database. The study included data of patients aged 18 years or older with venomous snakebite (n = 535), matched for propensity score with controls without venomous snakebite (n = 2140). The follow-up period was the duration from the initial diagnosis of venomous snakebite and administration of antivenom to the date of an acute stroke, or until 31 December 2013. The competing risk model was used to estimate the hazard ratio (HR) and 95% confidence intervals (CIs) of stroke, ischemic stroke and hemorrhagic stroke, after adjusting for demographic and other possible stroke risk factors. Results The adjusted HR for the venomous snakebite group compared with the control group was 2.68 for hemorrhagic stroke (95% CI = 1.35-5.33). Stratified analysis showed that the older age group (>65 years old) had a higher risk of hemorrhagic stroke. A 2.72-fold significant increase in the risk for hemorrhagic stroke was observed following venomous snakebite with antivenom usage (95% CI = 1.41–5.26). Conclusion Venomous snakebite is associated with an increased risk of hemorrhagic stroke after the use of antivenom. Further study of the underlying mechanism is warranted.