After more research, however, the doctors blamed an unexpected source, said Henry Spiller, director of the Kentucky Regional Poison Center:

A hookah.

Hookahs are water pipes in which tobacco is usually heated using charcoal and the smoke is cooled by water in the base. The tobacco is often flavored, and the smoke is usually drawn into the mouth and lungs through hoses, allowing more than one person to smoke at a time. They're commonly perceived as a less-toxic alternative for tobacco use.

But health officials and researchers say the ancient smoking method, which has its roots in the Middle East and India, may actually pose great health risks, including carbon-monoxide poisoning.

The male patient at Jewish, whom Spiller would not name, was treated in a hyperbaric oxygen chamber and recovered, Spiller said. A cigarette smoker may have a carbon-monoxide level of about 5 percent, but the male patient at Jewish was tested at about 29 percent, Spiller said.

"They're the levels we're used to seeing when you have furnace issues, house fires, car in the garage -- the really significant carbon-monoxide poisonings," Spiller said.

Hookahs and other water pipes have not faced the same sort of scrutiny from health researchers as cigarettes, but the risks are becoming better understood as the devices grow in popularity in the United States, said Thomas Eissenberg, a professor of psychology at Virginia Commonwealth University who has performed extensive research on such pipes.

The increased health risk of hookahs is partly because of how they're used. A cigarette smoker may take 10 puffs per cigarette; a hookah user may take 100 during a session, Eissenberg said.

And the Centers for Disease Control and Prevention says that, in a one-hour hookah session, the user inhales 100 to 200 times the volume of smoke inhaled from a single cigarette.

Increased levels of carbon monoxide stem from the charcoal used to heat the tobacco, the CDC said.

While the water in the hookah's base cools the smoke, making it more palatable than hotter cigarette smoke, it does not filter toxic materials from the tobacco, Eissenberg said.

Carbon-monoxide poisoning mimics other ailments, with many symptoms such as nausea and fatigue resembling influenza, Spiller said.

In severe cases, carbon-monoxide poisoning can lead to a coma or death, Spiller said.

Regular hookah users also risk long-term health problems from the increased levels of carbon monoxide, including neurological damage, Spiller said.

Carbon monoxide "blocks oxygen transport, but it also has a couple other mechanisms that if you do this chronically it continues to injure the brain," Spiller said.

"I'm afraid, for all I know, somebody who's been doing this a while -- 10 or 15 a year over a period, he may lose a few points of his IQ."

Donald Moore, 28, of Louisville, said he's assumed that smoking a hookah has risks akin to cigarettes.

For the past couple of years, Moore said, he's often smoked from a hookah and had tea with friends. He began smoking tobacco from a hookah to sate a desire for cigarettes, which he quit several years ago. Unlike cigarettes, hookahs are "not really an acquired taste" because of the water-cooled smoke, he said.

"At no point did I consider smoking from a hookah to be safer than a cigarette," Moore said. "It's going to give you cancer one way or another."

The carbon-monoxide risks were new to Moore, but he said the knowledge probably won't deter him.

Erin Lee's Smokey's Bean coffeehouse in Louisville mostly uses a mixture in its hookahst hat contains some tobacco but no nicotine and may be smoked indoors despite a citywide smoking ban, she said. The few Smokey's Bean hookah products that contain nicotine must be smoked outdoors, she said.

Lee said she's not concerned about health problems with her products because of the lack of nicotine.

Lee said hookahs are common at coffee shops on the West Coast, where she used to live.

"It's like a social thing, which I think goes hand and hand with coffee," Lee said.