More than 500 people have been sickened in an outbreak of vaping-related illness in the United States, health authorities said Thursday, as Los Angeles became the latest city to take steps to ban flavored e-cigarettes.

The known tally from the lung disease has jumped from 380 to 530, though the number of deaths stood unchanged at seven, according to a weekly report from the U.S. Centers for Disease Control and Prevention.

More than half of the cases involved patients under 25 years old and three-quarters were men, said Anne Schuchat, the centers' principal deputy director. Sixteen percent of those taken ill were under age 18.

E-cigarettes have been touted as a safer alternative to smoking. But critics say the risks are insufficiently understood, while flavored vaping liquids appeal particularly to children and risk getting them addicted to nicotine.

The U.S. Food and Drug Administration's laboratories are testing more than 150 samples of suspect product, but have yet to identify the substance responsible for the patients' severe pulmonary disease, said Mitch Zeller, who directs the administration's Center for Tobacco Products.

"There is no consistent pattern when it comes to ... what products plural are being used, how they're being used, where they might have been purchased, and what might have happened to the products along the way, from the time that they were put into the hands of the end user, to the moment of aerosolization, and, inhalation," Zeller said.

Investigators have so far been careful not to point the finger at any one brand, product or source.

Health authorities first realized in July that vaping was linked to the severe breathing difficulties, coughing, chest pain and even nausea being reported by young people.

Most reported that they had vaped cannabis-laced e-liquids, but some said they had used only nicotine products.

Reacting to the health scare, the state of New York banned flavored e-cigarettes Tuesday, effective immediately, following in the footsteps of Michigan which declared a ban earlier this month that has yet to go into effect.

On Thursday, the city attorney for Los Angeles, Mike Feuer, likewise recommended a citywide ban on flavored tobacco products.

And in India authorities announced on Wednesday a ban on the sale of all electronic cigarettes.