Fentanyl is a synthetic opioid that is quickly becoming a major contributor to the U.S. addiction crisis. Here are the top things to know about the drug. (Amber Ferguson/The Washington Post)

A Florida state attorney is voicing alarm after a 10-year-old boy died with a dangerous opioid mixture in his system — making him one of the state's youngest victims in the nationwide drug epidemic.

The Miami Herald reported that Alton Banks started vomiting June 23 after he returned to his Miami home from a community pool.

Authorities said the boy was later found unconscious and rushed to a nearby hospital, where he was pronounced dead. Preliminary toxicology results recently showed that the child had heroin and fentanyl in his system — a lethal mixture that has claimed numerous lives across the country, Miami-Dade State Attorney Katherine Fernández Rundle said. But the circumstances surrounding his death are still unknown, and the state attorney says she wants answers.

“How did this happen to a 10-year-old?” Rundle said to The Washington Post on Tuesday, noting that investigators do not suspect the child was exposed at home.

“It's the nightmare that every parent fears,” Rundle said. She said he was a happy-go-lucky boy “just doing what we want kids to do — be outside, be playful, be exploring, be with your friends.”

Rundle said the boy was a victim of “this terrible scourge that is running rampant in our country. Our community is not alone in this struggle. This epidemic has grasped and gripped communities everywhere.”

A spokeswoman for the Miami-Dade medical examiner’s office told The Post that she could not release any information because the case is under investigation.

Fentanyl can be prescribed as a legal painkiller, but its illicit use has experts particularly concerned amid a raging and relentless nationwide drug crisis.

Opioids, including heroin, fentanyl and other painkillers, are the main drivers of overdose deaths across the United States, according to data from the Centers for Disease Control and Prevention.

Opioid deaths have continued to spike, with more than 33,000 fatalities across the country in 2015 — the highest toll in recent history, according to data released by the CDC. As The Washington Post’s Christopher Ingraham reported, that marked an increase of nearly 5,000 deaths from 2014. Deaths involving synthetic opioids, such as fentanyl, rose by nearly 75 percent from 2014 to 2015.

In Florida, 3,228 people died from overdoses in 2015, a nearly 23 percent increase from the previous year, according to the CDC.

“When our innocent children are falling prey to these dealers of death, then it’s time — we need to take action, we need to be aware, we need to educate each other,” Rundle said.

A couple months ago, the opioid epidemic prompted Gov. Rick Scott (R) to declare a public health emergency.

Lawmakers in Florida recently passed legislation that imposes strict penalties for fentanyl-related crimes. The bill, which has been signed by the governor and goes into effect Oct. 1, among other things will allow authorities to charge dealers with murder when illegal distribution of fentanyl results in an overdose death.

The Drug Enforcement Administration has cautioned users about the dangers of the potent synthetic opioid but, more recently, has started warning first responders not to touch it.

In Connecticut last year, 11 SWAT officers were exposed to heroin and fentanyl after raw drug powder became airborne during a bust and, as a precaution, the entire team was taken to a hospital for treatment.

In May in Ohio, a police officer accidentally overdosed on fentanyl when he got a white powder on his hand. Paramedics gave him a dose of Narcan, an overdose antidote.

Marcel Casavant, chief toxicologist at Nationwide Children’s Hospital in Columbus, Ohio, said fentanyl can be inhaled, injected, and taken by mouth or through a patch on the skin. He conducted a study, which was published earlier this year, looking at calls that came through poison-control centers from 2000 to 2015 in the United States, reporting children being exposed to prescription opioids, including fentanyl.

Casavant, also the medical director of the Central Ohio Poison Center, said there were 222 fentanyl exposures among children younger than 5, 28 exposures among children 6 to 12, and 163 exposures among teens.

“The things we used to do to keep toddlers safe are not good enough to keep older children safe,” he said, noting that controlled medications should be kept locked away.

After the preliminary toxicology results in Alton's case, his mother, Shantell Banks, told the Miami Herald that her son, a fifth-grader at Frederick Douglass Elementary, was a “fun kid” who wanted to be an engineer when he grew up.

She said he was also a Carolina Panthers fan. “Cam Newton was his favorite football player,” she told the Herald.

Banks could not be reached for comment by The Post.

Asked about the preliminary findings in Alton's case, Joshua M. Sharfstein, an associate dean at the Johns Hopkins Bloomberg School of Public Health, said he had never heard of a case like it.

“It's a horrible situation and a devastating tragedy,” he said about the boy's death, “and it needs to be understood.”

This post has been updated.