An outbreak of a mysterious lung disease worsened over the last week with 805 confirmed or probable cases, a 52% surge over the previous week, the Centers for Disease Control and Prevention said Thursday.
At least 12 people have died across 10 states, the CDC said, citing data compiled through Tuesday.
Health officials still don't know what is making people sick. "Most patients have reported a history of using e-cigarette products containing THC. Many patients have reported using THC and nicotine. Some have reported the use of e-cigarette products containing only nicotine," CDC said.
The CDC confirmed 530 probable cases and seven deaths as of Sept. 17. The increase in cases from last week represents new cases and recent reporting of previously identified cases. Patients have been found in 46 states, up from 38 last week, and one U.S. territory.
The disease is impacting mostly men, and all reported cases have a history of e-cigarette or vaping use, health officials said. Two-thirds of the victims are ages 18 to 34 and 16% are under age 18, the CDC said.
The CDC has dispatched more than 100 doctors and investigators to identify the specific cause of the deadly illness, which resembles a rare form of pneumonia. Early symptoms include coughing, shortness of breath, fatigue, chest pains, nausea, vomiting and diarrhea.
U.S. lawmakers are seizing on the outbreak to scrutinize the e-cigarette industry. A House panel that is investigating the market leader Juul pressed a top CDC official on Tuesday for answers on what's making people sick.
Health and Human Services Secretary Alex Azar said President Donald Trump is preparing a ban on flavored e-cigarettes, which have been scrutinized by officials for their appeal to children.
State and local governments are already banning sales.
Michigan is the first state to ban sales of flavored e-cigarettes, while San Francisco became the first U.S. city to prohibit the sales of flavored e-cigarette products.
Public health officials, in the meantime, are urging consumers not to use e-cigarettes or other vaping products. The CDC also recommends not using vaping products off the street and not adding substances to products that are not intended by the manufacturer.
—CNBC's Angelica LaVito contributed to this report.