Aerial mosquito spraying could occur earlier and more often this year, as a result of new state guidelines for battling Eastern equine encephalitis.

An expert panel — convened ­after the state was criticized for not proactively spraying mosquito-­killing pesticides last summer — concluded that Eastern equine encephalitis is an annual risk for Massachusetts residents. The findings led the state Department of Public Health to ­announce this week that it will lower the threshold for considering when to spray and will research new spraying tactics to target disease-bearing mosquitoes.

Last summer, two cases of Eastern equine encephalitis were contracted in Southeastern Massachusetts, one of them fatal.

“EEE and other mosquito-borne illnesses represent a serious public health concern for Massachusetts families,” John Auerbach, commissioner of public health, said in a statement. “These revised guidelines will ensure that we mount the most effective science-based approach to reduce the risk of disease spread by mosquitoes among our residents.”

The creation of the panel, which included specialists from around the country, was prompted by an outcry from several health agents in towns across Southeastern Massachusetts. In December, they sent a joint letter to Auerbach, urging more aerial spraying and asking that the region be considered to be at high risk for Eastern equine encephalitis. None of the health agents could be reached Thursday.

Members of the panel agreed that the disease has evolved from occurring sporadically, with some years of no cases, into an annual event.

“I think EEE is out there every summer,” said Dr. Richard Pollack, a Harvard instructor and chairman of the mosquito advisory group. “Sometimes we’ve just gotten lucky and not had any ­humans infected.”