WASHINGTON — Sixteen states have now reported 153 cases of serious, vaping-related respiratory illnesses in the past two months, and many of the patients are teenagers or young adults.

In a statement on Wednesday, the Centers for Disease Control and Prevention said that all of the cases occurred in people who acknowledged vaping either nicotine or tetrahydrocannabinol, known as THC, the high-inducing chemical in marijuana.

Federal and state officials say that they are mystified as to what is causing the illnesses, but that it does not appear that an infectious disease is responsible. No one product or device is common among the cases, the agency said. It also was unclear whether a contaminant in a used cartridge or a home-brewed concoction of vaping liquids contributed to some of the ailments.

The patients, most of whom were adolescents or young adults, were admitted to hospitals with difficulty breathing. Many also reported chest pain, vomiting and fatigue.