WASHINGTON (Reuters) – At least 1,013 people died of overdoses in several U.S. cities from 2005 to 2007 after illegally injecting the highly potent painkiller fentanyl, U.S. officials said on Thursday.

The fentanyl, at least some of which came from Mexico, was sold illegally by drug dealers on U.S. streets, sometimes mixed with cocaine and heroin, according to a report issued by the U.S. Centers for Disease Control and Prevention.

The Chicago area had the most deaths with 349, followed by Philadelphia with 269, the Detroit area with 230. Other deaths were reported in St. Louis, Missouri, and the states of Delaware and New Jersey.

Emergency medical personnel reported finding some victims with the needle still in their arms, not having completed the injection because the drug was so powerful, said retired CDC public health service officer Dr. Stephen Jones, who wrote the report.

The fentanyl caused perhaps hundreds of other deaths not reflected in the official tally of 1,013 deaths, Jones said in a telephone interview.

“I think this is an extraordinary episode of fatal drug overdoses. But it’s got to be recognized as part of the bigger problem of the increasing numbers of drug overdose deaths in the United States.”

The number of deaths from drug overdoses and other cases of unintentional drug poisonings jumped from 11,155 in 1999 to 22,448 in 2005, the CDC noted, with powerful painkilling drugs playing an important role.

The fentanyl used in Chicago and Detroit was believed to have come from an illicit production facility in Toluca, Mexico, that was shut down by authorities in May 2006, the CDC said.

Fentanyl is used medically to treat pain in cancer patients and others but also is abused for recreational use.

“One gram of pure fentanyl can be cut into approximately 7,000 doses for street sale. Manufacture of (fentanyl) requires minimal technical knowledge, and recipes for making (fentanyl) are available on the Internet,” according to the report.

“The unknowns of what somebody can obtain on the streets and misuse are a very obvious message from this outbreak,” Nick Reuter of the U.S. Substance Abuse and Mental Health Services Administration said in a telephone interview.

Jones said the recent deaths marked the worst known outbreak of U.S. fentanyl deaths. An earlier series of deaths in the 1980s included at least 110 fatal overdoses, he said.

(Editing by Maggie Fox and Bill Trott)