NEW YORK — Hundreds more Americans have been reported to have a vaping-related breathing illness, and the death toll has risen to 12, health officials said Thursday.

The Centers for Disease Control and Prevention said 805 confirmed and probable cases have been reported, up 52% from the 530 reported a week ago. At this point, illnesses have occurred in almost every state.

The confirmed deaths include two in California, two in Kansas, and one each in Florida, Georgia, Illinois, Indiana, Minnesota, Mississippi, Missouri and Oregon. The Mississippi death was announced by officials in that state Thursday.

Over the summer, health officials in a few states began noticing reports of people developing severe breathing illnesses, with the lungs apparently reacting to a caustic substance. The only common factor in the illnesses was that the patients had all recently vaped.

As a national investigation started and broadened, reports have increased dramatically.

It’s not clear how many of the 275 added cases occurred in the last week, and how many are being logged long after they happened. The CDC has not released details on when symptoms began in each case.

The agency’s count includes only illnesses that have met certain criteria. Other illnesses are also being investigated.

Most patients have said they vaped products containing THC, the ingredient that produces a high in marijuana. The investigation has been increasingly focused on products containing THC, with some attention on ingredients added to marijuana oil.

But some patients have said they vaped only nicotine. Currently, health officials are advising people not to use any vaping product until the cause is better understood.