Doctors warn that chronic kidney disease caused by heat stress could be a major health problem for millions of workers worldwide as the temperature rises over the next decade.
They believe that more research is needed into the possible links between heat and CKDu chronic renal disease of uncertain origin to determine the extent of the problem.
CKDu is a different form to chronic kidney disease (CKD), which causes progressive loss of kidney function. This condition is most common in elderly people or those with other conditions like diabetes and hypertension. However, CKDu epidemics have already begun to spread in rural areas of El Salvador and Nicaragua. There, abnormally high numbers have died from irreversible kidney damage.
CKDu is also being reported to affect large numbers of manual workers in hot environments in Central America and South America.
The fluid balance of the body is controlled by kidneys, making them especially sensitive to extreme temperatures. It is becoming increasingly clear that CKDu should not be considered a heat-related injury. This is because workers are sustaining subtle damage to their kidneys every day while working in the field. This can lead to severe kidney disease and complete renal failure.
The repetitive, low-grade attack on the kidneys doesn't always cause symptoms. Workers may not be aware that they are becoming sicker over time, until it becomes so severe that they have end-stage renal disease. Dr Cecilia Sorensen, Columbia University director of the global consortium for climate and health education, stated that workers might not know they are suffering from this condition.
She said that we don't know the extent of the problem because we aren't doing surveillance. While there are certain hotspots, it's not clear if they are widespread or how severe the problem is.
However, the documented epidemics share similar characteristics. People who are affected often work in heat conditions outside and are from economically and socially disadvantaged backgrounds with limited access to healthcare or insurance.
During a demonstration in Nicaragua, where CKDu has claimed the lives of tens of thousands of workers, a former sugarcane worker with kidney issues, left, a mock coffin was carried by the man. Photograph: Esteban Flix/AP
According to Sorensen, the severity of kidney damage increases the more vulnerable and depressed the worker. According to Sorensen, those who are not able to control their work conditions or are incentivised by employers to work longer hours without breaks (e.g. workers paid for the number of berries picked or the amount of sugar cane cut) are most likely to be the worst affected.
They are getting sick because of the work they do, but there is no way to stop it. There is very little regulation in the workplace that would prevent this. She said that it is a major blind spot and a human rights problem.
Ramn Garca Trabanino is a clinical nephrologist who is also the medical director at El Salvadors Centre of Hemodialysis. He first noticed an unusually high number of CKD patients in his hospital when he was a medical student over two decades ago.
He said that they were young men and were dying because we did not have the funds or the ability to provide dialysis treatment. They died every day, and we did our best to help them.
He has been researching similar epidemics in Mexico and Costa Rica since then.
You will see that the maximum temperatures maps for Central America match the regions in which we describe the disease. Every year, we fight for the top spot for the country with the highest CKD mortality. Our mortality rates are 10 times higher that what we should be expecting. It is impossible to find new patients.
While the majority of scientists agree that CKDu is caused by heat exposure and dehydration (the consensus view), some scientists believe that CKDu may also be related to genetic makeup and risk factors such as poverty, malnutrition and other social determinants.
Professor Richard Johnson of the University of Colorados School of Medicine said that recurrent heat stresses are not just a problem in Nicaragua's sugarcane fields. It isn't as well-known that heat stress and dehydration could be a factor in kidney disease in our societies.
Professor Tord Kjellstrom of the Australian National University's national centre of epidemiology and population Health said heat stress isn't getting the attention it deserves in discussions about how to reduce the worst effects of climate change.
The number and intensity of heat days will increase, and working people will have to face greater challenges in avoiding heat stress. This is especially true for the two-thirds who live in sub-tropical and tropical areas. Kjellstrom, who was also a member of the Intergovernmental Panel on Climate Change, stated that heat exhaustion can threaten the livelihoods and hamper efforts to reduce poverty.
Global warming is a grave threat to the lives of workers and the livelihoods for millions. If we want to be able to deal with the future, emerging policies on climate must reflect this.
