Time to treatment and severity of snake envenoming in Brazil

To analyze the relationship between time to treatment and severity of snakebite envenomation in Brazil.

This case-series retrospective study analyzed 144 251 snakebite cases in Brazil between 2007 and 2015, as reported to the Brazilian Notifiable Diseases Information System. The main dependent variable was snakebite envenomation severity (mild/moderate/severe). The main predictor was time to treatment (early (< 6 hours) vs. delayed (≥ 6 hours)). Covariables were snake type (Bothrops/Crotalus/Micrurus/Lachesis), patient's age and sex, bite site, and treatment at a specialized care center (center/noncenter). Polytomous logistic regression techniques were used to control the covariates and assess confounding and effect modification.

The time to treatment variable was strongly associated with the severity of snakebite envenomation. Snake type and treatment at specialized care center modified the main association effect. The association between delayed time to treatment and envenomation severity was consistently stronger among patients treated at specialized care centers than among those who were not treated at such centers. Odds ratios tended to increase significantly from moderate to severe envenomation for cases within the subgroups "Center + Bothrops" (1.37 to 2.05), "No center + Bothrops" (1.25 to 1.47), "Center + Crotalus" (1.35 to 3.03), "No center + Crotalus" (0.97 to 2.72), and "Center + Lachesis" (1.22 to 1.89).

This study confirmed the classical hypothesis that the time between snakebite and initiation of medical care is associated with severity of snakebite envenomation. It is therefore necessary to provide snakebite victims early access to specialized medical care, particularly to antivenom therapy.