Snakebites and climate change in California, 1997-2017.

Background: Climate change effect on flora and fauna has been scientifically documented, but the effect on North American venomous snakebites is unknown. The objectives were to examine Californian snakebite incidence and correlate with weather patterns and climate changes.

Methods: A retrospective analysis of snakebites reported to the Californian Poison Control System from 1 September 1997 to 30 September 2017. Venomous snakebite reports were aggregated by caller zip code, and correlated per county with weather data, air temperature, precipitation, population data, eco-regions, and land characteristics. Time series decomposition by seasonality and trend, regression, and autocorrelation were used to assess association between climate variables and incidence.

Results: There were 5365 reported venomous snakebites during the study period, with a median age of 37 years (22-51) with 76% male (p < .001, 95% CI 75.6-77.9%). Most snakebite outcomes were coded as minor (1363, 25%) or moderate (2607, 49%), with three deaths. Adjusted for population, the annualized incidence of snakebites statewide slightly decreased (rho = -0.11, p = .65). The snakebite incidence per million people rose after a period of no drought and declined during drought (r = -0.41, p ≪ .01). Snakebite incidence decreased by 6-month prior drought (-3.8% for each 10% increase in drought), and increased by 18-month prior precipitation (+3.9% for each 10% increase in precipitation).

Conclusions: Patterns of precipitation and drought had a significant and predictive effect on snakebites in California over a 20-year period. Snakebite incidence decreased following drought, and increased after precipitation.