The hoaxes are so widespread, health experts are actively refuting them to alert the press and calm frantic callers.
A few weeks ago, America's imminent health danger was flesh-eating bacteria carried by bananas from Costa Rica.
Before that, the menace du jour was infected hypodermic needles planted in theater seats and pay phone coin-return slots.
And this week, apparently, you should look out for the dreaded Klingerman Virus, which reportedly has killed _ and we're only talking in confirmed cases here _ seven unsuspecting people who received in their mailboxes a blue envelope labeled, "A gift for you from the Klingerman Foundation."
As surely as a cocktail of Pop Rocks and soda didn't kill Mikey, the Life cereal spokesboy, none of those "health threats" is true. But like the genre's sibling, the urban myth, medical myths are being carried across the nation like spores on the wind by the Internet and the fears of people willing to believe the worst.
They are a growing problem for the public health officials who must debunk them.
The Centers for Disease Control and Prevention, in fact, has been so bombarded by frantic calls from the public and press about such hoaxes that it has begun issuing written statements to refute them.
The May issue of the venerable Mayo Clinic's Women's HealthSource newsletter also seeks to put several myths to rest and warn readers against falling for new ones.
"We just recently had been getting tons of letters from women who were terrified that they were going to get breast cancer from their deodorant or flesh-eating bacteria from their bananas," explained Michelle Felten, managing editor of the newsletter.
Mayo didn't want to bestow credibility on the hoaxes by printing them, but the sheer volume of inquiries convinced the editors it was time to tell the public, "This is just hooey," she said. "Use your common sense. If it sounds too bizarre to be true, it probably is."
In this week's e-mail alert about the Klingerman Virus, people were warned the blue envelope from the fictitious Klingerman Foundation contained a small sponge contaminated with a "strain of virus . . . not previously encountered."
It said that the virus causes dysentery and that at least seven of the 23 confirmed victims have died. It names the CDC, the U.S. Postal Service and state health departments as the sources and warns, "PLEASE PASS THIS ON TO EVERYONE YOU CARE ABOUT."
People fall for these hoaxes for a variety of reasons, experts say.
The most successful ones achieve an air of credibility by blending shreds of real science, medical terms and authoritative sources like the CDC.
Their explanations also seem somewhat plausible.
Take, for instance, the one about deodorants and breast cancer: The e-mail explained that antiperspirants block sweat glands, which keeps the body from purging toxins. Those toxins collect in the lymph nodes under the arms, which eventually causes cell mutations and cancer in the breast.
Nice try, but no way.
The flesh-eating banana bulletin warned that the bug that causes necrotizing fasciitis had learned to graft itself to fruit skin and that contaminated bananas had arrived from Costa Rica.
The U.S. Food and Drug Administration knew of the problem, the alert said, but failed to warn the public because the agency feared a banana panic.
The CDC got so many calls about the bananas that it posted a bulletin on its Web site, http://www.cdc.gov, explaining that it's impossible to catch flesh-eating bacteria from fruit. The agency posted a similar message regarding Klingerman's, as did the Florida Department of Health.
"We do what we can to set the record straight when there's enough e-mail traffic going on," CDC spokesman Tom Skinner said.
And doctors who doggedly work to spread messages of good health _ don't smoke, exercise, eat right _ say they're frustrated by how easily medical myths can grab the public's attention, while their warnings of real disease often go unheeded.
"Prevention, like washing hands, it's just not a sexy topic for the public," lamented Dr. Joseph Yao, an infectious disease specialist at the Mayo Clinic in Jacksonville.
"Whereas if we have flesh-eating bacteria . . . death, heroic surgery, losing limbs _ these are always things that will catch people's eyes."