A woman smokes an E-Cigarette at Digital Ciggz in San Rafael, California.Justin Sullivan | Getty ImagesThe number of cases of a deadly vaping illness continues to rise “at a brisk pace” with 18 confirmed deaths and more than 1,000 cases in almost every state across the U.S., according to the Centers for Disease Control and Prevention. The CDC has identified 275 new cases over the last week and is investigating several other deaths that are suspected of being caused from vaping, Dr. Anne Schuchat, the CDC’s principle deputy director, told reporters on a conference call Thursday. “We haven’t seen a measurable drop in the occurrences of new cases,” she said.Doctors still don’t know what’s making people sick, Schuchat said. Of the 578 cases where doctors know what patients were using, roughly 78% of them said they vaped THC, the active ingredient in marijuana, while 17% percent said they exclusively used nicotine, according to the CDC. The number of deaths jumped from 12 confirmed fatalities last week to 18 this week, the CDC said. It’s proving to be an especially deadly illness for older adults. “The fatalities that we’re seeing tend to be a bit older,” she said, adding that the media age among the deceased is close to 50 while the median age among all patients is 23. The CDC has dispatched more than 100 physicians and investigators since the lung disease started to emerge as a public health threat in July. Doctors initially said the illness resembled a rare for pneumonia, caused by oil in the lungs, but new research casts doubt on that theory.Researchers at the Mayo Clinic published a study Wednesday said a mix of “toxic chemical fumes,” not oils as previously expected, may be what’s making patients sick. They examined lung biopsies from 17 patients suspected of having the mysterious illness.Public health officials are urging consumers not to use e-cigarettes or other vaping products in the meantime. The CDC also recommends not using vaping products off the street and not adding substances to products that are not intended by the manufacturer.This is a developing story. Please check back for updates.