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

Erica Chavez Santos, June T Spector, Jared Egbert, Jennifer Krenz, Paul D Sampson, Pablo Palmández, Elizabeth Torres, Maria Blancas, Jose Carmona, Jihoon Jung, John C Flunker, Erica Chavez Santos, June T Spector, Jared Egbert, Jennifer Krenz, Paul D Sampson, Pablo Palmández, Elizabeth Torres, Maria Blancas, Jose Carmona, Jihoon Jung, John C Flunker

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.

Keywords: Agricultural workers; Core body temperature; Heat education and awareness tools (HEAT); Heat strain; Heat stress; Heat-related illness; Intervention study; Physiological strain index.

Conflict of interest statement

The authors declare that they have no competing interests.

© 2022. The Author(s).

Figures

Fig. 1
Fig. 1
Study flow
Fig. 2
Fig. 2
Scatter plot of maximum Heat Index and PSI by effort level. Lines are unadjusted regression lines using linear models
Fig. 3
Fig. 3
Box plot of maximum PSI by effort and group status. C = comparison; I = intervention groups
Fig. 4
Fig. 4
Box plot of maximum PSI by number of reported HRI symptomsa. aN = 65 unique participants with PSI and HRI symptoms data within a week of field PSI measurement, 121 observations

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