Native Americans may be the most affected by the opioid epidemic that has spread across the U.S., and federal officials are looking for solutions.

A hearing Wednesday in the nation’s capital shed light that overdose deaths in Native American communities have skyrocketed in the time the epidemic has swept America.

Native Americans and Alaska Natives saw a fivefold increase in overdose deaths between 1999 and 2015, Dr. Michael Toedt told the U.S. Senate Committee on Indian Affairs.

Centers for Disease Control and Prevention figures indicate the increase in that period was higher for Native Americans than any other group, jumping to roughly 22 deaths for every 100,000 people in metropolitan areas, and nearly 20 for every 100,000 people in non-metropolitan areas.

But the statistics, while staggering, may represent an undercount for Native Americans and Alaska Natives by as much as 35 percent, because death certificates often list them as belonging to another race, said Toedt, who is the Indian Health Services’ chief medical officer.

The hearing in Washington comes as a growing number of tribes file lawsuits against drug manufacturers and distributors, saying they misrepresented addiction risks.

A few states over on Wednesday Milwaukee County officials filed suit against 13 drug companies on behalf of county taxpayers claiming 336 people died from opioids in the county last year, more than double the number from five years earlier, according to Fox 6 Milwaukee.

“Make no mistake, there is blood on their hands and there should be a stain on their conscience,” Milwaukee County Corporation Counsel Margaret Daun told Fox 6 Milwaukee.

Federal officials, back in D.C., said the opioid epidemic is straining tribal resources.

U.S. Attorney John Anderson of New Mexico said tribal leaders in a northern stretch of the state had called for solutions.

One pueblo police chief described losing a brother and sister to overdoses, he said.

“The opioid epidemic knows no boundaries,” Anderson said, “and so our pueblos are equally affected by heroin and prescription opioids.”

Several senators questioned whether a decline in prosecutions in Indian Country cases also had contributed to the crisis.

“We need a plan and it can’t just be about treating the addiction,” said Sen. Heidi Heitkamp, D-N.D. “It needs to be a plan that gets law enforcement on the ground.”

The Associated Press contributed to this report.