Authorities in New Orleans are seeing an alarming increase in fatal overdoses involving fentanyl, a synthetic opioid and powerful anesthetic that increasingly has been mixed into — and, in some instances, sold as — heroin.

While the drug has surfaced in “sporadic bursts” over the years, it now appears to have become something of its own trend, said Keith Brown, special agent in charge of the U.S. Drug Enforcement Administration’s New Orleans field office.

The drug largely has been sold on the heroin market without buyers’ knowledge, Brown said, “but it is starting to supplant, combine with or just replace heroin in some markets.”

“Fentanyl has become a huge problem, especially in contributing to the spike in overdoses,” Brown said in an interview. “We’re seeing more and more of it in the metro area, just like we’re seeing more and more of it across the South, the mid-South and even across the country.”

The Orleans Parish Coroner’s Office counted at least nine overdose deaths in the first quarter of this year in which users had lethal levels of fentanyl in their system.

By comparison, the drug — which is many times stronger than heroin and, in its legal form, is intended to manage intense pain — was found in just two drug-related deaths in New Orleans in all of last year, said Dr. Jeffrey Rouse, the parish coroner. In both of the 2014 cases, fentanyl appeared to be related to medical use and was not the sole cause of death.

“Even if you count those two, compared to annualized year-to-date numbers, we are looking at a significant increase” in 2015, Rouse said.

One of the fatalities this year involved “the person’s first use of what was thought to be heroin,” Rouse said. Other cases have involved longtime drug users.

“We are seeing persons who, by all accounts, appear to be experienced heroin users,” Rouse said. “We’re talking about people who know what they’re doing and are dying with needles in their arms.”

Rouse said he suspects the New Orleans deaths actually involve a compound called acetyl fentanyl, an opioid that is technically different from fentanyl but has similar effects.

Acetyl fentanyl is not approved for any medical use in the United States. “Our laboratory testing does not distinguish between the two” substances, he said.

Heroin laced with acetyl fentanyl has been blamed for fatal overdoses for at least the past couple of years in Jefferson Parish. Seven fatal overdoses involving the drug were recorded in 2013 and again in 2014, and the parish already has seen five fatal overdoses related to acetyl fentanyl in 2015, said Mark Bone, chief death investigator for the Jefferson Parish Coroner’s Office.

“A lot of people are substituting acetyl fentanyl for heroin,” said Dr. Gerry Cvitanovich, the Jefferson coroner.

The DEA issued a nationwide alert earlier this year regarding the soaring use of fentanyl, a drug it described as being up to 50 times more powerful than heroin. The drug, which is cheaper than heroin, has been introduced into the heroin supply to dilute the heroin and make it go further, said Brown, the DEA agent.

“People just really don’t know how to handle it,” Brown said. “It’s not being cut right, and it’s being added into heroin by people that couldn’t bake a cake, let alone make drugs.”

Federal authorities also have warned law enforcement agencies about the danger of officers absorbing fentanyl through their skin or inhaling it as airborne powder.

Officer Frank Robertson, a New Orleans Police Department spokesman, said detectives in the city have not encountered a spike of fentanyl cases. But according to the DEA’s National Forensic Laboratory Information System, state and local laboratories around the country reported 3,344 fentanyl submissions last year, compared with just 942 in 2013.

“It’s not just in New Orleans,” Brown said. “It’s in Baton Rouge. It’s in Alabama. It’s in Jackson, Mississippi.”

Deaths involving acetyl fentanyl could be undercounted because it is not part of many screens for illicit drugs. Dr. Beau Clark, the East Baton Rouge Parish coroner, said authorities there are monitoring for the drug but have not seen any fatal cases.

The uptick in deaths involving fentanyl and its related compounds comes as the total number of fatal heroin overdoses in Louisiana appears to be stabilizing to some degree after drastic increases in recent years, according to state and local figures.

In New Orleans, there were a total of 14 drug-related deaths in the first quarter of this year in which investigators detected heroin, compared with 48 such cases in all of last year, according to the Coroner’s Office. Jefferson Parish has recorded at least 18 heroin-related deaths this year, compared with 66 in 2014.

Follow Jim Mustian on Twitter, @JimMustian.