Parents in New Jersey are concerned after a state medical examiner determined a virus causing severe respiratory illness across the country is responsible for the death of a 4-year-old boy.

Hamilton Township health officer Jeff Plunkett said the Mercer County medical examiner's office found the death of Eli Waller was the result of enterovirus D-68. Waller, the youngest of a set of triplets, died in his sleep at home on Sept. 25.

The virus has sickened more than 500 people in 43 states and Washington, D.C.— almost all of them children. Waller is the first death in New Jersey directly linked to the virus.

School officials are awaiting test results on a second child at Yardville Elementary School in Hamilton Township, MyFoxPhilly.com reported. According to the news site, the boy was Waller’s classmate.

At a community meeting held Sunday, parents called for better communication from school officials.

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"They're not saying this is over with. And I guess that's what I need to hear, that it was an isolated case. It's not," Linda Bonfonti, who has a grandchild in the school district, told MyFoxPhilly.com.

District officials said a complete scrub-down in the schools was ongoing, and that they are continuing to examine their protocol, the news site reported.

Waller was asymptomatic before his death, and the onset of his illness was rapid, Plunkett said.

He stayed home from school Sept. 24 with a case of pink eye, but the medical examiner found that to be unrelated to the virus.

The U.S. Centers for Disease Control and Prevention said earlier this week that four people infected with the virus had died, but it's unclear what role the virus played in the deaths.

Some children are especially vulnerable to infection due to pre-existing conditions, but the medical examiner said that was not the case in the New Jersey boy's death. Most of the severe cases nationwide have involved children because they generally have not been exposed to enteroviruses as often as adults have and are less likely to have developed an immunity to them, officials say.

The boy's family released a statement Sunday and have asked for privacy.

"My words probably won't capture him well, but everyone who met Eli knows how he made people feel; imagine a shy little puppy who wants only to make people proud and happy, maybe tripping a bit over his own paws, but truly full of unconditional love. He was a beautiful mix of hesitancy, need and striving, caution and surprise, all of which were grounded in a pure, unconditional love," Andy Waller, Eli's father, said in the statement.

"The youngest of a set of triplets, born much smaller and lighter than his sisters, Eli nevertheless persevered through all the difficulties that came his way. Eli was not the type to give up, and even though things never really came easily to him, he would just plug away, day after day, practicing sounds, or movements, or skills, until he would eventually get them," the statement read.

"He did this entirely in an effort to make his Mom and Dad pround and we can unequivocally say that we were, and will continue to be, so very proud of our little Eli." Andy said.

The family is working to create "The First Day School Foundation," which aims to provide support for students involved in special education.

"Like so many kids his age, Eli was both nervous and excited about starting school, and it is our sincere hope that this Foundation can work to help kids in a way that will make Eli proud of us all, in the same way that we were all so proud of him," the family said.

"When you're given the news that a virus was the cause of death to your child, of course they were saddened, even more so because they won't get the answers or closure they need," Mayor Kelly Yaede said. "The mother said, `We will never find out where he contracted this.'"

The enterovirus germ is not new. Most people who catch the virus experience only a runny nose and low-grade fever. It was first identified in 1962 and has caused clusters of illness before.

This year, the virus has gotten more attention because it has been linked to hundreds of severe illnesses. Beginning last month, hospitals in Kansas City, Missouri, and Chicago have received a flood of children with trouble breathing.

Reuters and The Associated Press contributed to this report.