People living near gas hydraulic fracturing sites are more concerned than had been thought about possible health effects of the drilling, U.S. researchers say.

Dr. Poune Saberi of the Perelman School of Medicine at the University of Pennsylvania and the Center of Excellence in Environmental Toxicology and colleagues collected responses from 72 adults visiting a primary care physician's office in the hydrofracking-heavy area of Bradford County, Pa.

The study participants volunteered to complete an investigator-facilitated survey. Twenty-two percent of the participants said the hydrofracking might be the cause of such health concerns as sinus problems, sleeping difficulties and gastrointestinal problems.