Objectives To examine the association between workload and kidney injury in a fieldworker cohort with different levels of physically demanding work over a sugarcane harvest, and to assess whether the existing heat prevention efforts at a leading occupational safety and health programme are sufficient to mitigate kidney injury.
Methods Biological and questionnaire data were collected before (n=545) and at the end (n=427) of harvest among field support staff (low workload), drip irrigation workers (moderate), seed cutters (high) and burned sugarcane cutters (very high). Dropouts were contacted (87%) and reported the reason for leaving work. Cross-harvest incident kidney injury (IKI) was defined as serum creatinine increase ≥0.30 mg/dL or ≥1.5 times the baseline value, or among dropouts reporting kidney injury leading to leaving work.
Results Mean cross-harvest estimated glomerular filtration rate change was significantly associated with workload, increasing from 0 mL/min/1.73 m2 in the low-moderate category to −5 mL/min/1.73 m2 in the high and −9 mL/min/1.73 m2 in the very high workload group. A similar pattern occurred with IKI, where low-moderate workload had 2% compared with 27% in the very high workload category. A healthy worker selection effect was detected, with 32% of dropouts reporting kidney injury. Fever and C reactive protein elevation were associated with kidney injury.
Conclusions Workers considered to have the highest workload had more cross-harvest kidney damage than workers with less workload. Work practices preventing heat stress should be strengthened and their role in preventing kidney damage examined further. Future occupational studies on chronic kidney disease of unknown aetiology should account for a healthy worker effect by pursuing those lost to follow-up.
- Heat stress
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Presented at A previous version of parts of this work has been presented as a poster and conference abstract at the Third International Workshop on Chronic Kidney Diseases of Uncertain/Non-Traditional Etiology in Mesoamerica and Other Regions, March 2019 in San José, Costa Rica.
Contributors CW, DHW and JG conceived and CW prepared the first protocol draft. The final protocol was produced with essential input from IW and KJ. SP, IW and CW collected the field data. DHW was the principal investigator and supervised the project. CW and EH were responsible for data management and statistical analyses. UE and JA were responsible for laboratory analyses. EH was responsible for drafting the manuscript, with input from all authors. All authors contributed to the revised drafts with text and/or intellectual content. All authors of this article have read and approved the final version submitted.
Funding This research was funded via the Adelante Initiative, a multistakeholder programme working to improve labour conditions in the sugarcane industry and beyond. Funding was provided by the German Investment Corporation (DEG) and the Ingenio San Antonio (ISA) sugar mill via the DEG’s technical support programme for loan recipients. Under the technical support programme, the DEG funds half of the programme and the loan recipient, ISA in this case, the other. Laboratory analyses were paid directly to Lund University by ISA from the matching funds designated to the technical support programme. The remaining funds from ISA were dedicated to the logistical operations required by the mill to run its field interventions. DEG and Stavros Niarchos Foundation provided funds directly to the non-governmental organisation, La Isla Network, to pay for the management and execution of the research. Gothenburg and Lund Universities also supported the work by inkind funding.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval This study was approved by the Comité de Ética para Investigaciones Biomédicas (CEIB), Facultad de Ciencias Médicas, Universidad Nacional Autónoma de Nicaragua (UNAN - León (FWA00004523/IRB00003342). The biochemical investigation carried out at the Division of Clinical Chemistry and Pharmacology at Lund University in Sweden was approved by the Regional Ethical Review Board in Lund (reg no 2018–256).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement No data are available.
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