A decade ago, Baltimore saw a stretch of drug overdoses similar to the more than two dozen reported cases on a single day this week that spun up a frenetic response from law enforcement, medical personnel and harm reduction advocates.

It was the summer of 2015 and Baltimore’s health commissioner at the time, Dr. Leana Wen, heard from community leaders in a meeting about “bad batches” of drugs.

The substance turned out to include fentanyl, a powerful synthetic opioid that was 50 times more powerful than what many heroin users had been used to.

“EMS would see a spike of overdoses in West Baltimore and then a hospital would say they saw patients around this time, but no one knew if they were connected,” Wen said in an interview Friday.

The meeting gave rise to a new kind of campaign in the city dubbed “Don’t Die,” a call-out to educate health care and drug treatment providers and the public.

City officials wanted to warn them about these batches of pills or powder seen as “bad” because the drugs had been adulterated with something potentially life-threatening that wasn’t advertised by the street dealers. Wen said she paired those efforts with the wide distribution of the opioid reversal medication naloxone along with the proper training to deploy it.

Despite those efforts, opioids, most notably fentanyl, became entrenched as a particular scourge in the city. And the efforts today to identify and track down the origins of the latest “bad batches” remains an uphill fight.

Officials say they can’t always quickly link up overdoses to a particular batch because people use the drugs alone and sometimes say they don’t seek care even if they overdose, according to Wen and other experts.

The market for illegal drugs used in the city also has only become more treacherous because of the proliferation of new and dangerous contaminants, experts said in interviews this week.

On Thursday, dozens were treated at area hospitals for overdoses linked to a suspected “bad batch” of drugs, according to law enforcement officers and community advocates. In the days ahead, officials said, they will investigate to see if there are more victims, what they consumed and how it got to all those people clustered near Pennsylvania and North avenues.

The broad investigation includes scientists like Edward Sisco, who said he expects to receive samples of the alleged bad batch for examination. He’s a research chemist at the National Institute of Standards and Technology, whose lab now partners with 80 sites, such as treatment centers, in 15 states including Maryland, which send him trace amounts of drugs for testing.

Sisco said in an interview Friday that he looks for the presence of dangerous additives, and increasingly, the proportions of each, to spot trends that could be harmful to drug users.

He said over the years, fentanyl completely replaced heroin because of cost and access to the synthetic painkiller, with chemical ingredients largely originating in makeshift Chinese labs.

Law enforcement officials say drug dealers shipped their products, sometimes through the U.S. mail, to Mexico and trucked them over the border. Along Interstates 95 and 81 and other highways, they reached Baltimore and other Maryland cities.

From there, established sellers found ready buyers. Some of those consumers had become hooked on prescription medications which later led them to fentanyl. Others had begun using street drugs recreationally.

When the group assembled by Wen learned from each other about a spike in overdoses — defined as three or more linked overdoses — a text alert would ping community treatment providers and users warning them about the dangers of a “bad batch” on the street.

Wen acknowledged in an interview Friday, however, that the approach had to be scaled back after some consumers used the health warnings as more of a tip sheet to find more powerful drugs.

Sisco, the drug scientist, said illegal drug samples from Maryland that he has analyzed in recent years contained xylazine, an animal tranquilizer that also causes deep wounds where people inject the drugs. Last year, he said other tests of drugs advertised as fentanyl also contained BTMPS, a chemical used in plastic production.

More recently, his tests have revealed the presence of medetomidine, which is similar to xylazine, and local anesthetics like lidocaine.

He said they are likely causing a lot of mass overdoses, but it’s usually not immediately clear because of that shadowy nature of use.

Sometimes, the quick spike in overdoses does become public. In 2018, for example, more than 90 people overdosed at the same time in a New Haven, Conn., park on a synthetic cannabinoid known as K2.

There are also new risks as some consumers have figured out how to make online orders for drugs directly from vendors in China and other countries, said John Cook, a Baltimore-Washington area official from the High Intensity Drug Trafficking Areas program, which was created by the U.S. Congress to assist law enforcement.

He said cartels manufacturing products are known by law enforcement officials to adulterate fentanyl with other drugs specifically to make them more attractive by trying to “extend the ‘high.’” They also give them catchy street names.

The chemicals from China added to recreational illegal drugs aren’t made by professionals and can be especially dangerous, said Ibrar Mian, the U.S. Drug Enforcement Administration’s special agent in charge for the Washington region.

But Mian said they can make pills indistinguishable from prescription oxycodone, Xanax and Adderall, and estimates 5 of every 10 of those pills could be deadly. Naloxone, he said, only reverses an overdose of an opioid like heroin or fentanyl and has no effect on many of the dangerous additives.

Cook called this week’s mass overdoses in Baltimore “an extremely concerning event and the magnitude is significant. The preparation by emergency responders for such an event likely saved many lives.”

The only way to prevent another mass overdose?

Mian says, “No one should be consuming.”

Banner reporter Justin Fenton contributed to this article.