"We haven't seen a measurable drop in the occurrences of new cases," she said. "The data that we've seen doesn't suggest it has peaked, it doesn't suggest this is declining."

Schuchat called it a "very concerning outbreak" with no signs of abating.

The CDC has identified 275 new cases over the last week and is investigating several other deaths that are suspected of being caused by vaping, Dr. Anne Schuchat, the CDC's principle deputy director, told reporters on a conference call Thursday.

The 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 throughout the U.S., according to the Centers for Disease Control and Prevention.

The CDC has confirmed 1,080 probable cases across 48 states and the U.S. Virgin Islands so far.

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.

"In light of the seriousness of this condition," consumers should stop vaping, particularly THC and especially anything bought off the street, she said, or any substance not intended by the manufacturer.

The number of confirmed fatalities jumped from 12 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 median 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 form of pneumonia, caused by oil in the lungs, but new research casts doubt on that theory.

Researchers at the Mayo Clinic published a study Wednesday that said a mix of "toxic chemical fumes," not oils, may be what's making patients sick. They examined lung biopsies from 17 patients suspected of having the mysterious illness.

"CDC will continue to work with FDA and state health partners to investigate the cause, or causes, of this outbreak and to bring an end to these lung injuries," CDC Director Robert Redfield said.

WATCH: Juul ramps up lobbying efforts as vaping backlash grows