A Case-Crossover Study of Heat Exposure and Injury Risk in Outdoor Agricultural Workers

Abstract

Background: Recent research suggests that heat exposure may increase the risk of traumatic injuries. Published heat-related epidemiological studies have relied upon exposure data from individual weather stations.

Objective: To evaluate the association between heat exposure and traumatic injuries in outdoor agricultural workers exposed to ambient heat and internal heat generated by physical activity using modeled ambient exposure data.

Methods: A case-crossover study using time-stratified referent selection among 12,213 outdoor agricultural workers with new Washington State Fund workers' compensation traumatic injury claims between 2000 and 2012 was conducted. Maximum daily Humidex exposures, derived from modeled meteorological data, were assigned to latitudes and longitudes of injury locations on injury and referent dates. Conditional logistic regression was used to estimate odds ratios of injury for a priori daily maximum Humidex categories.

Results: The mean of within-stratum (injury day and corresponding referent days) standard deviations of daily maximum Humidex was 4.8. The traumatic injury odds ratio was 1.14 (95% confidence interval 1.06, 1.22), 1.15 (95% confidence interval 1.06, 1.25), and 1.10 (95% confidence interval 1.01, 1.20) for daily maximum Humidex of 25-29, 30-33, and ≥34, respectively, compared to < 25, adjusted for self-reported duration of employment. Stronger associations were observed during cherry harvest duties in the June and July time period, compared to all duties over the entire study period.

Conclusions: Agricultural workers laboring in warm conditions are at risk for heat-related traumatic injuries. Combined heat-related illness and injury prevention efforts should be considered in high-risk populations exposed to warm ambient conditions in the setting of physical exertion.

Fig 1. Sensitivity analyses.

1 primary analysis (N = 51,801); 2 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) that occurred on weekends (included n = 43,531); 3 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with locations based only on zip code or city (included n = 32,810); 4 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with injury locations based only on first healthcare address (included n = 44,498); 5 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with geocoding accuracy scores less than 0.80 (included n = 47,588); 6 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with injury times that were not between 5:30 am and 4:30 pm (included n = 43,808); 7 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with injury times that were not between 5:30 am and 12:30 pm (included n = 30,870); 8 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with more than seven days of time-loss (included n = 42,885); 9 sensitivity analysis with maximum daily dry air temperature instead of Humidex (N = 51,801); 10 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) that resulted in death (included n = 51,776); 11 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with more than one day between the injury date and the first visit to a healthcare provider (included n = 30,758); 12 sensitivity analysis excluding from primary analyses injuries (and corresponding referent days) with injuries that occurred on public holidays (n = 49,713).