Heat exposure and kidney health of Costa Rican rice workers

Abstract

Background/Aim: Chronic kidney disease of unknown etiology (CKDu) affects populations along the Pacific coast of Mesoamerica including the Guanacaste province of Costa Rica. Although the etiology of CKDu is unclear, it is known to be associated with heavy labor in hot environments. The aim of this longitudinal study was to describe heat exposure and renal health of Costa Rican rice workers over three months of production.Methods: We collected pre-shift urine and blood samples from 72 workers with different jobs in a rice company at baseline and three months later. Metabolic and ambient heat loads were measured for each job using the WBGT index (wet bulb globe temperature) and NIOSH guidelines. Serum creatinine (S-Cr, mg/dl) was used to estimate glomerular filtration rate (eGFR) as the main outcome.Results: Participants were 20-62 years old (41.2±10.3) and educational levels ranged from zero to university (mean 7 years). Most participants (90%) were dehydrated (USG≥1.025) in at least one of the two pre-shift measurements while 35% of all workers were dehydrated in both samples. At baseline mean S-Cr was 1.22 mg/dL in field workers and 1.12 mg/dL in non-field workers (p=0.083) and three months later levels were 1.35 mg/dL and 1.12 mg/dL respectively (p=0.008). The only predictor of low eGFR identified using multiple logistic regression analysis was being a field worker. Low eGFR was seen in 18.5% of field workers and 4.3% of non-field workers at baseline. Three months later, when workloads were higher, 25.6% of field workers (n=7) and 6.7% of non-field workers (n=4) had low eGFR (p=0.034).Conclusions: Dehydration was quite common in this study. Low eGFR was particularly prevalent in field workers in heat stress conditions. There is an urgent need to continue to improve efforts to provide adequate water, rest and shade for heat-exposed workers in accordance with national regulations.