The effect of the participatory heat education and awareness tools (HEAT) intervention on agricultural worker physiological heat strain: results from a parallel, comparison, group randomized study

Abstract

Background Farmworkers are at risk of heat-related illness (HRI). We sought to: 1) evaluate the effectiveness of farmworker Spanish/English participatory heat education and a supervisor decision-support mobile application (HEAT intervention) on physiological heat strain; and 2) describe factors associated with HRI symptoms reporting. Methods We conducted a parallel, comparison group intervention study from May–September of 2019 in Central/Eastern Washington State, USA. We used convenience sampling to recruit adult outdoor farmworkers and allocated participating crews to intervention (n = 37 participants) and alternative-training comparison (n = 38 participants) groups. We measured heat strain monthly using heart rate and estimated core body temperature to compute the maximum work-shift physiological strain index (PSImax) and assessed self-reported HRI symptoms using a weekly survey. Multivariable linear mixed effects models were used to assess associations of the HEAT intervention with PSImax, and bivariate mixed models were used to describe factors associated with HRI symptoms reported (0, 1, 2+ symptoms), with random effects for workers. Results We observed larger decreases in PSImax in the intervention versus comparison group for higher work exertion levels (categorized as low, low/medium-low, and high effort), after adjustment for maximum work-shift ambient Heat Index (HImax), but this was not statistically significant (interaction − 0.91 for high versus low/medium-low effort, t = − 1.60, p = 0.11). We observed a higher PSImax with high versus low/medium-low effort (main effect 1.96, t = 3.81, p < 0.001) and a lower PSImax with older age (− 0.03, t = − 2.95, p = 0.004), after covariate adjustment. There was no clear relationship between PSImax and the number of HRI symptoms reported. Reporting more symptoms was associated with older age, higher HImax, 10+ years agricultural work, not being an H-2A guest worker, and walking > 3 min to get to the toilet at work. Conclusions Effort level should be addressed in heat management plans, for example through work/rest cycles, rotation, and pacing, in addition to education and other factors that influence heat stress. Both symptoms and indicators of physiological heat strain should be monitored, if possible, during periods of high heat stress to increase the sensitivity of early HRI detection and prevention. Structural barriers to HRI prevention must also be addressed. Trial registration ClinicalTrials.gov Registration Number: NCT04234802, date first posted 21/01/2020.

How Does Environmental Temperature Affect Farmworkers’ Work Rates in the California Heat Illness Prevention Study?

“…Educational campaigns for farmworkers and supervisors have been shown to increase workers' knowledge of best practices for HRI prevention 30,31 . However, the evidence that they result in empirical measures of decreased HRI or dehydration is weaker 32 . Heat-related illness may also be underrecognized by both workers and clinicians, 33 and workers may need targeted interventions to recognize symptoms of HRI and learn appropriate first aid 34 .…”

“… 30 , 31 However, the evidence that they result in empirical measures of decreased HRI or dehydration is weaker. 32 Heat-related illness may also be underrecognized by both workers and clinicians, 33 and workers may need targeted interventions to recognize symptoms of HRI and learn appropriate first aid. 34 It also remains unquantified how effective the existing California HRI prevention standard is to date, 23 with more research needed to target further policy changes.…”

Considerations for occupational heat exposure: A scoping review

“…prevention program called Heat Education and Awareness Tools (HEAT) uses a social-ecological model approach that has been successful among agricultural labourers [102]. HEAT training uses an engaged and relational approach to learning, taking into consideration the perspectives and satisfaction levels of employees, as well as accounting for risk factors at multiple levels (individual, interpersonal, supervisor, and community) [101].…”