Central American Kidney Disease Epidemic Linked to Occupational Heat Exposure.

For two decades, Nicaragua and El Salvador have seen increasing mortality from an unusual form of chronic kidney disease (CKD), also called Mesoamerican Nephropathy (MeN). The disease has disproportionately affected sugarcane and other agricultural workers, and appears to be unrelated to traditional kidney disease risk factors such as diabetes. Researchers from the School of Public Health have been collaborating with researchers from the region since 2008, but the specific cause or causes of the disease remain unknown.

Now, a new study by the research team adds to the evidence that the CKD epidemic in the region is linked to occupational heat exposure.

The study, published in the American Journal of Kidney Diseases, found 12.1 percent of a sample of artisanal brick makers in Nicaragua had CKD, and that the disease was particularly common among individuals who worked with the ovens for baking bricks.

“We knew from going to the health clinic in La Paz Centro that kidney disease was a real problem, but we did not anticipate how high the prevalence would be, or how severe some of the cases,” says Madeleine Scammell, associate professor of environmental health and one of the study’s two senior authors.

“Clinicians in the region have also said that sugarcane workers are not the only people affected by this disease, despite the media attention they receive, and we were told by brick makers that oven workers were at greatest risk,” she says. “It turns out their observations were spot-on.”

The researchers gathered data from 224 workers at brickmaking facilities in La Paz Centro, a municipality in northwestern Nicaragua, in February and June of 2016. This sample constituted about 44 percent of the brick makers in La Paz Centro.

The brick makers were all between 18 and 60 years old, had been working in brickmaking for at least a year, and had been working for no more than two hours on the mornings when researchers collected blood and urine samples to estimate kidney function. The brick makers answered questions about their roles in the brickmaking process, their working hours, their height and weight, how much water and alcohol they normally drank, whether they smoked, how long they had worked in brickmaking, their histories of diabetes and hypertension, their education levels, and whether they had immediate family members with CKD.

The researchers found that 12.1 percent of the brick workers had stage 3 to 5 CKD. Operating the ovens, less education, older age, and having an immediate family member with CKD were all associated with worse kidney function. The biggest risk factors for a decline in kidney function during the study period were drinking less than three liters of water during a working shift and working for more than 48 hours per week.

The researchers noted that the workers who tended and/or loaded the ovens often worked more hours than those whose roles involved other parts of the brickmaking process. However, while the sample only included 32 women, these women were just as likely to work with the ovens as men—but none of them had CKD. This may be an area for further study, the authors wrote, as is the question of whether CKD runs in families because of genetic factors or because brickmaking—like agriculture and other industries where CKD is common—itself runs in families.

Since completing the study, the research team in Nicaragua has begun collaborating with a local nephrologist to host monthly clinics in La Paz Centro to provide additional care and follow-up for CKD patients, Scammell says.

Lead authorship of the study was shared by Caryn Sennett, who was an SPH master’s student during the study, and Lyanne Gallo Ruiz, who was a medical student at the National Autonomous University of Nicaragua (UNAN). Senior authorship was shared by Scammell and Marvin González Quiroz, an instructor at UNAN.

The other SPH co-authors were: doctoral student Komal Basra; Rebecca Laws, who was a postdoctoral associate during the study; Yorghos Tripodis, research associate professor of biostatistics; Daniel Brooks, associate professor of epidemiology; and Michael McClean, professor of environmental health.

The other co-authors were: Damaris Lopez Pilarte and Juan José Amador, formerly of the Nicaraguan Ministry of Health and now full-time BU researchers in Nicaragua; Mauricio Sánchez Delgado, Ana García Urbina, Tania Gámez Altamirano, and Aurora Aragón of UNAN; and Joseph Kupferman and David Friedman of Harvard Medical School.

—Michelle Samuels