More than 1,800 people have been sickened with a lung illness tied to vaping, according to data from the Centers for Disease Control and Prevention.

The outbreak, which began ramping up in late August, has killed 37 people in 24 states. It has afflicted patients in nearly every state, the District of Columbia and the U.S. Virgin Islands, suggesting the culprit is a product (or products) available nationwide or online. The only state that hasn’t reported a confirmed case is Alaska.

The CDC investigation is ongoing as cases continue to rise. While the agency has not identified the cause of the lung disease or any potential products or brands involved, it reported that THC vaping cartridges have been used by most patients. Additionally it noted that often the products are from informal sources – either bought on the street or obtained from friends and family.

The patient age is beginning to skew younger. According to the CDC, 79% of patients are under 35, with a median age of 24. But the age of patients who died from the illness is older, with a median age of 53. The CDC also reported that 70% of patients are male.

This follows trends for vaping use overall. In 2017, 2.8% of adults, or about nine million people, were current e-cigarette users, according to the CDC. Underage teens make up about a third of that, with the CDC reporting in 2018 that 3.6 million U.S. middle and high school students have used e-cigarettes in the past 30 days.

Last month, CDC officials noted that the rate of new cases had slowed, but the pace has picked up again. Officials are attributing that slowdown to reporting lags.