TRENTON, N.J. (AP) — A New Jersey medical examiner says a virus that has been causing severe respiratory illness across the country is responsible for the death of a 4-year-old boy.

Hamilton Township health officer Jeff Plunkett says the medical examiner determined the death of Eli Waller was the result of enterovirus 68.

The virus has sickened more than 500 people in 43 states and Washington, D.C. — almost all of them children. Earlier this week, the U.S. Centers for Disease Control and Prevention said four people infected with the virus had died but what role it played in the deaths was unclear.

Some children are especially vulnerable to infection because of pre-existing conditions, though the medical examiner said that was not the case in the New Jersey death.

Township officials say the boy’s parents have asked for privacy.