Fatal Snakebite Envenoming and Agricultural Work in Brazil: A Case-Control Study

We investigated the association between fatal snakebite envenoming and agricultural work in Brazil, considering the effects of relevant covariables. A nested case-control study was performed using 1,119 fatal cases of snakebite envenoming among persons aged ≥ 10 years, notified to the Brazilian official reporting system, from 2004 to 2015. As controls, 4,476 cases were randomly selected from the 115,723 nonfatal cases of snakebite, without missing data, that occurred in the same time period. The main predictor was occupation in the agriculture sector; the main outcome was death by snakebite envenoming. Logistic regression analysis was used to investigate the main association, controlling for the effects of relevant covariables. Fatal cases had a 20% greater chance (odds ratio [OR] = 1.20; 95% confidence interval [CI]: 1.00-1.39) of being among farmers than the controls. However, late (≥ 6 hours) time to treatment (OR = 2.00; 95% CI: 1.70-2.36); adequate antivenom with an insufficient (OR = 1.25; 95% CI: 1.04-1.50) or excessive (OR = 4.89; 95% CI: 4.10-6.03) number of vials; inadequate antivenom and insufficient or excessive number of vials (OR = 3.87; 95% CI: 2.40-6.24); no use of antivenom (OR = 2.05; 95% CI: 1.60-2.64); and age ≥ 60 years (OR = 1.98; 95% CI: 1.61-2.44) were more strongly associated with lethality. Lethality was 1.0% in the period, being 0.47% among those receiving early and adequate treatment. We concluded that in Brazil, fatal snakebite envenoming was associated with agricultural work, controlling for relevant covariates. However, quality of health care provided and greater age were much more strongly associated with lethality.