Dysuria and medical events related to heat stress and muscle injury among male Nicaraguan sugar cane workers

Abstract

Background. Nicaraguan sugar cane workers have an elevated prevalence of chronic kidney disease of unknown origin (CKDu). CKDu pathogenesis may involve environmental heat exposure along with generation of mechanical heat, providing an opportunity for recurrent heat stress and muscle injury with subsequent kidney injury. A common urinary symptom among at-risk workers is dysuria. Compared with other job types, cane cutters may be at elevated risk of these potential intermediate events, though longitudinal studies are limited.Methods. Using employment data for male workers at a Nicaraguan sugar cane company, we classified active work months as cane cutting or non-cane cutting for each month of follow-up, July 1993 through June 2010. Based on medical records, we determined occurrence of: dysuria, heat-related events, and muscle-related events during follow-up. Dysuria was defined as pain upon urination without other explanatory cause. Heat-related events included heat stress or experiencing >=2 heat symptoms. Muscle-related events were defined to identify potential rhabdomyolysis. Associations between cane cutting and each outcome were analyzed using logistic regression based on generalized estimating equations for repeated events, controlling for age.Results. The 242 workers contributed 13,530 active work months, with 22.4% of person-months classified as time worked in cane cutting. There were 376 dysuria events, 35 heat-related events, and 32 muscle-related events. Cane cutting months exhibited a higher odds of dysuria and heat-related events [dysuria: OR=1.67 (95% CI: 1.18-2.37); heat: 1.97 (0.92-4.22)] compared with non-cane cutting months. The associations with cane cutting strengthened after subjects had worked >=60 months [dysuria: OR=2.70 (95% CI: 1.72-4.24); heat: 3.05 (1.22-7.61)]. No association was observed for muscle-related events.Conclusions. Working in cane cutting compared with working in a different job was associated with increased dysuria and heat-related events, supporting the hypothesis that cane cutters are at increased risk of events suspected of inducing or presaging CKD.