The number of vaping-related illnesses in the U.S. could soon climb much higher, a health official told a hearing convened by an Illinois congressman Tuesday.

Anne Schuchat, of the Centers for Disease Control and Prevention, told a Congressional subcommittee that she believes “hundreds more” lung illnesses have been reported to health authorities since last Thursday, when the CDC put the tally at 530 confirmed and probable cases.

Nine deaths have been reported; the first was in Illinois.

The subcommittee is led by U.S. Rep. Raja Krishnamoorthi, a Democrat from northwest suburban Schaumburg.

The CDC is investigating the little-understood outbreak but has not yet identified a common electronic cigarette or ingredient.

The illnesses, which resemble an inhalation injury, have triggered a swift backlash against e-cigarettes, including a proposed federal ban on flavors by the Trump administration and an end to sales in Walmart stores nationwide. Michigan and New York have also called for state-level restrictions.

Under questioning from House Democrats at the first congressional hearing on the emerging problem, Schuchat emphasized how little is known about the effects of inhaling various oils, flavor particles and other ingredients in vaping products.

“We don’t know enough about the aerosol that vaping produces in terms of the short and longer-term health impacts,” said Schuchat. “It may indeed be that the process itself is risky.”

Many patients reported vaping THC from marijuana, but Schuchat and state health officials have cautioned that some said they only vaped nicotine.

The CDC is recommending that people not use e-cigarettes at all while authorities investigate.

Krishnamoorthi slammed Food and Drug Administration regulators for not requiring more testing of nicotine-containing e-cigarettes.

“When a product is released onto the market without safety testing or clinical trials, this is what we fear,” said Krishnamoorthi, who chairs the economic subcommittee of the House Committee on Oversight and Reform.

The FDA gained authority to regulate the products in 2016, but repeatedly pushed back the timeline for reviewing their health effects. The current deadline for submitting products is next May.

Lawmakers also heard from the mother of 18-year-old Piper Johnson of southwest suburban New Lenox, who was rushed to the emergency room in mid-August with chest pain, difficulty breathing, coughing and nausea.

Her mother, Ruby Johnson, told lawmakers the problems emerged while she was driving Piper to start her freshman year of college in Colorado.

“What started as an exciting rite of passage turned into a terrifying near-death experience that involved a weeklong hospital stay,” said Johnson, detailing a battery of drugs and medical interventions used to treat her daughter, including oxygen, intravenous fluids, steroids, anti-nausea drugs and pain relievers.

Johnson said her daughter had vaped THC but was mainly using nicotine e-cigarettes such as Juul in the weeks before she became sick. Johnson blamed e-cigarette manufacturers for targeting teens with appealing flavors and the FDA for allowing vapes to “proliferate, flourish and remain for purchase,” without formal review.

Illinois health officials have been investigating dozens of cases of people being hospitalized with serious lung problems after they used e-cigarettes or other vaping products. Officials have confirmed at least 16 cases where people with a history of vaping were hospitalized with a respiratory illness.

Illinois officials on Aug. 23 reported what they consider the first death in the nation linked to vaping after the person contracted a serious lung disease. Officials did not release further details, including the identity or location of the person, or what kind of vaping product was used.

Public health officials have labeled underage vaping an epidemic and new survey data shows the problem worsening. Nearly 28% of high school students reported vaping in the last month, according to preliminary CDC figures for 2019. That number is up from 21% last year and 12% the year before.

WBEZ news producer Araceli Gómez-Aldana and the Associated Press contributed.