Researchers at the University of Arizona will be launching a study of how prone Hispanic children are to asthma in Tucson compared with their peers on the other side of the U.S.-Mexico border in Nogales, Sonora.

The study will follow 500 pregnant women of Mexican descent in both cities and their newborns for the next five years to see how prevalent asthma is.

Dr. Fernando Martinez, a principal investigator of the project and director of the University of Arizona Health Sciences Asthma and Airway Disease Research Center, said there is four times less asthma in Nogales, Sonora, than in Tucson, which is about an hour's drive away.

A study of teenagers in Nogales, Arizona, showed 16% had asthma compared with 4% to 6% of teens in the same age range just across the border in Nogales, Sonora. Mexicans who come to the United States also have less asthma than Mexican Americans, researchers have found.

The Arizona Daily Star reported that the University of Arizona study will look into how the risk of asthma is affected by the “hygiene hypothesis,” which suggests that a child's reduced exposure to germs stunts their immune system's ability to fight infectious organisms.

Martinez said studies have shown children in Nogales, Sonora, are exposed to harmful bacteria that cause many infections but also protective bacteria that bolster their immune systems.

“Paradoxically, in the middle of all the poverty and underdevelopment in many barrios and colonias in Nogales, Sonora, there is less asthma,” he said. “We want to learn which bacteria children in Nogales, Sonora, are exposed to that Tucson children are not exposed to that leads to asthma.”

The study was delayed due to COVID-19, but researchers plan to begin enrolling pregnant women in August and finish by August 2023. The study will collect blood and stool samples from the women while pregnant, and samples from their children over the years. Researchers also will study children's diets, illnesses, development, vaccine history and environmental dust and water samples from their homes.