Workload and cross-harvest kidney injury in a Nicaraguan sugarcane worker cohort

Abstract

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.

Keywords: CKDu; Heat stress; Inflammation; Kidney; Workload.

Figure 1

Median (solid blue line) and 90% range (grey dotted lines) wet-bulb globe temperature (WBGT) in the sugarcane fields of Ingenio San Antonio (ISA) during harvest in 2017–2018. The ISA rest schedules during harvest in 2017–2018 are compared with the American Conference of Governmental Industrial Hygienists (ACGIH) recommendations for heavy physical work according to the median WBGT. *Threshold limit values (red dashed lines) for the number of minutes of rest per hour recommended by the ACGIH for heavy physical work.

Figure 2

Participant flow chart. ISA, Ingenio San Antonio; SCr, serum creatinine.

Figure 3

Renal function (eGFR) by job and time of testing. Dashed lines indicate median (black) and 90% range (grey) eGFR in administrative staff at baseline. BeGFR denotes mean (95% CI) baseline eGFR. ΔeGFR denotes mean (95% CI) cross-harvest change in eGFR. Includes only workers measured before and at the end of harvest. eGFR, estimated glomerular filtration rate. EPI denotes eGFR is estimted according to the Chronic Kidney Disease Epidemiology Collaboration equation.