PORTLAND (AP) — The number of gonorrhea cases in Maine has more than quadrupled in the past four years, concerning public health officials.

The Maine Center for Disease Control and Prevention said there were 441 reported cases of the sexually transmitted disease as of Dec. 14 this year, up from 98 reported cases in 2008.

More than half of those cases are in people in their 20s.

Dr. Stephen Sears, state epidemiologist, told The Portland Press Herald the trend is “concerning,” but mirrors national figures. He said the exact reason for the rise is a mystery.

He said the state needs to launch a public education campaign.

Sears said the Maine CDC will review this year’s cases in the coming weeks to look for patterns among various racial, gender and age groups.