Kidney Function in Rice Workers Exposed to Heat and Dehydration in Costa Rica

Abstract

The aim of this study was to evaluate heat exposure, dehydration, and kidney function in rice workers over the course of three months, in Guanacaste, Costa Rica. We collected biological and questionnaire data across a three-month-period in male field (n = 27) and other (n = 45) workers from a rice company where chronic kidney disease of unknown origin (CKDu) is endemic. We used stepwise forward regression to determine variables associated with estimated glomerular filtration rate eGFR at enrollment and/or change in eGFR, and Poisson regression to assess associations with incident kidney injury (IKI) over the course of three months. Participants were 20−62 years old (median = 40 in both groups). Dehydration was common (≥37%) in both groups, particularly among other workers at enrollment, but field workers were more exposed to heat and had higher workloads. Low eGFR (<60 mL/min/1.73 m2) was more prevalent in field workers at enrollment (19% vs. 4%) and follow-up (26% vs. 7%). Field workers experienced incident kidney injury (IKI) more frequently than other workers: 26% versus 2%, respectively. Age (β = −0.71, 95%CI: −1.1, −0.4), current position as a field worker (β = −2.75, 95%CI: −6.49, 0.99) and past work in construction (β = 3.8, 95%CI: −0.1, 7.6) were included in the multivariate regression model to explain eGFR at enrollment. The multivariate regression model for decreased in eGFR over three month included current field worker (β = −3.9, 95%CI: −8.2, 0.4), current smoking (β= −6.2, 95%CI: −13.7−1.3), dehydration (USG ≥ 1.025) at both visits (β= −3.19, 95%CI: −7.6, 1.2) and pain medication at follow-up (β= −3.2, 95%CI: −8.2, 1.95). Current fieldwork [IR (incidence rate) = 2.2, 95%CI 1.1, 5.8) and being diabetic (IR = 1.8, 95%CI 0.9, 3.6) were associated with IKI. Low eGFR was common in field workers from a rice company in Guanacaste, and being a field worker was a risk factor for IKI, consistent with the hypothesis that occupational heat exposure is a critical risk factor for CKDu in Mesoamerica.

Keywords: agricultural workers; chronic kidney disease; heat exposure; hydration; occupational.

Figure 1

Selection of study participants. Two women were employed, and one provided informed consent, but had incomplete samples at follow-up. Only men are included in the analysis and shown here.

Figure 2

(a) WBGT from 7:00 am–12:50 pm during study days in March (enrollment) and May (follow-up) outdoors (usual shift 6:00 am–1:00 pm with workers eating lunch in the field under a roof at approximately noon) and indoors from 8:00 am to 2:50 pm (usual shift 8:00 am–5:00 pm). The Occupational Safety and Health Administration (OSHA) recommended limits for moderate work (28 °C), and heavy work (26 °C) in acclimatized workers is indicated by the red lines. Median WBGT were 30.9 °C and 32.0 °C outdoors in compared to 27.4 °C and 27.7 °C indoors. (b) Average WBGT by time in outdoor (blue) and indoor (green) conditions in March (baseline, dark blue and dark green) and May (follow-up, light blue and light green) are shown in figure b. The OSHA recommended limit for moderate work which applied to both field and other workers on some days (27.8 °C), is shown in orange, and the limit for heavy work, which applied to field workers on some days (26.1 °C), is shown in red.