The 35 people who are thought to have died of drug overdoses in just five days this month ranged in age from 19 to 66, the Philadelphia Department of Public Health said Monday. Sixty-nine percent of the victims were male and 60 percent were non-Hispanic whites.

Emergency departments around the city reported treating a spike in  nonfatal overdoses over the same period, although the increase — 171 from Dec. 1 to 5— was not as extreme as the death count suspected by the Medical Examiner's Office.

About 700 deaths in Philadelphia were identified as drug-related in 2015, or just under two per day. There were 12 deaths on the first day of the recent spike alone — considerably more than the number of fatalities the Medical Examiner's Office normally sees from all causes.

"This sharp rise in fatal overdoses occurred in the context of an escalating public health problem in Philadelphia, which may experience as many as 900 overdose deaths in 2016. Fentanyl has been increasingly involved in fatal overdoses," the health department said in Monday's update.

All of the drugs involved in the most recent spate of deaths will not be confirmed until toxicology tests are completed, a process that typically takes eight weeks. Meanwhile, the cases are suspected of being due to unintentional drug overdoses, based on autopsy findings, evidence at the scene, and other circumstances.

Police, too, are not expected to conclude their investigation for some time.

Chief Medical Examiner Sam. P. Gulino said last week that 184 drug-related deaths in 2015 had tested positive for fentanyl and that he projected that number would rise to at least 300 this year. Final results will not be known until all tests are back, probably in March.

The U.S. Centers for Disease Control and Prevention reported last week that more than 52,000 Americans died from drug overdoses in 2015, or 16.3 per 100,000 residents, up 11 percent from the previous year.

The CDC said heroin deaths were up 21 percent nationally (and 21 percent in New Jersey and 30 percent in Pennsylvania).

Federal data do not track fentanyl separately, but the agency said that the synthetic opioid would be the dominant factor in a broader category that was up about 73 percent. That same category rose 100 percent in Pennsylvania and 125 percent in New Jersey, according to CDC statistics.

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