The Food and Drug Administration should have acted sooner to curb the surge in youth vaping, the acting head of the agency, Dr. Ned Sharpless, told a House subcommittee Wednesday in his first appearance before Congress since news of severe lung illnesses linked to vaping began to circulate this summer.

State health departments in nearly every state tell NBC News that they are actively investigating more than 1,000 cases of the illnesses. That's higher than the Center for Disease Control and Prevention's official case count, currently at 530, which only includes confirmed or probable cases. Ten people have died.

But despite investigations by hundreds of physicians, state health officials, the FDA and the CDC, no single ingredient or product has been identified as the cause of the illnesses.

The FDA has received 300 vape product samples, and has tested about half for the presence of nicotine, THC (the psychoactive ingredient in marijuana), painkillers, cutting agents, pesticides and toxins.

About half of the products that contained THC also contained an ingredient vitamin E acetate, said Sharpless. That's an oil that has "no business being in lungs."

But there's no evidence that one ingredient can explain all of lung illnesses. Health investigators say it's likely there are multiple causes.

"There may be a particular problematic source in California, and something different going on on the East Coast," said Dr. Anne Schuchat, the CDC's principal deputy director. Schuchat also testified before the subcommittee Wednesday.

She said the tedious investigation cannot keep up with the fast-moving spate of illnesses.

"The data are coming in as we speak," Schuchat said. "I’m extremely frustrated with the pace of our investigation."

Sharpless also told legislators that the FDA is finalizing plans to remove flavored electronic cigarettes from the marketplace, and will begin enforcing the "existing law that limits the marketing of such products" in the coming weeks.

That means flavored e-cigarettes would essentially be banned from being sold, unless companies can provide evidence their products would benefit public health.

Some states have already enacted temporary bans on flavored vapes, including Michigan, New York and Rhode Island. Massachusetts went one step further, banning all vaping devices for 4 months.

But Sharpless could not guarantee mint and menthol — favored by a third of young people who vape — will be part of the Trump administration's anticipated enforcement action.

The plan of action that comes after years of skyrocketing rates of kids and teenagers using e-cigarettes.

"In retrospect, the FDA should have acted sooner," Sharpless said.

Others in public health say they, too, are impatiently waiting for answers, but insist a thorough and careful investigation is crucial.

"We understand it’s a broad and deep analysis, and we want to make sure we go after the correct substance," Dr. Lee Norman, secretary of the Kansas Department of Health and Environment, told NBC News.

But he added, "The sooner the better."

"This is an epidemic," he said, "and it's getting worse."