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(Reuters) - U.S. health officials said on Thursday two more deaths occurred since last week from a mysterious respiratory illness tied to vaping, taking the total toll to 54.

The Centers for Disease Control and Prevention (CDC) also reported 97 more hospitalized cases from 50 states, the District of Columbia, and two U.S. territories, as of Dec. 17. The number of people hospitalized now stands at 2,506.

The deaths have been confirmed in 27 states and the District of Columbia, and the CDC said more deaths are under investigation.

U.S. officials in November reported the discovery of Vitamin E acetate — believed to be used as a cutting agent in illicit vaping products containing marijuana components — in all lung samples from 29 patients.

CDC has called Vitamin E acetate as a “chemical of concern” and recommended the substance not be added to e-cigarette, or vaping products, while the investigation is ongoing.