The Internet's power to make something "go viral" has surpassed the phrase's original meaning.
Sneeze once, you might pass a virus to the person next to you. Post something online, the entire world might get infected.
Take the H1N1 vaccine: Late last month, the search term "H1N1 vaccine dangers" hit Google's top 10 searches.
A video of a cheerleader supposedly crippled after getting the flu vaccine received almost a million hits.
It's driving doctors crazy, as they insist the vaccine is safe and anti-vaccine preachers are plain wrong. But the H1N1 story is evidence of a broader trend: The public's appetite for Internet health information has fundamentally altered the doctor-patient relationship.
"People don't have that kind of patriarchal relationship with their physicians anymore," said Dr. Maxine Barish-Wreden, who heads Sutter Medical Center's integrative medicine team. "They come in, and they're armed with some data already."
Almost all U.S. physicians said in a survey that at least some patients bring to appointments health information they found online, according to the Manhattan Research Group, a company that researches health care trends.
Sometimes it means those precious few minutes with the doctor can be spent setting the patient on the right track.
"There's such a fine line between somebody who's well-informed and somebody who's misinformed," said Diane Chan, a pediatrician at Kaiser's Roseville, Calif., Medical Center. "Because then I have two jobs: One, to convince you you don't have a disease that you think you do, and then to diagnose you with the right thing."
Sixty-one percent of Americans look online for health information, the majority of whom say their last search had an impact on medical decisions, according to a 2009 survey from the Washington-based Pew Research Center.
Evelyn Meletlidis of Roseville said she looks up health information online every day because she has an autistic 4-year-old. She belongs to Internet groups for parents of kids with autism.
Her choice not to continue vaccinating her son was a decision made after extensive research online and offline, she said, and one not welcomed by doctors.
"I've been literally kicked out of offices because I won't vaccinate my child," she said.
Despite all the online information, Pew researchers also found the Internet hasn't replaced doctors.
"People turn first to their doctor, then to Dr. Mom, and third to Dr. Google," said Suzanne Fox, one of the Pew study authors.
Roughly two-thirds of doctors think online health research is a good thing, according to the Manhattan Research Group.
When harnessed in the correct way, doctors say, the Internet makes the patient a partner, not a passive bystander. If a patient already has researched a specific condition, it means a physician can bypass the basics and get right down to real questions.
Some providers have tapped into this thirst for knowledge with their own online information channels. Patients at Kaiser Permanente can log onto an interactive Web site and find information and videos on topics such as how to prepare for a major surgery.
Dr. Kristopher Kordana said e-mail has made his internal medicine practice more patient-centered, as counterintuitive as that sounds.
Kordana, who works at Kaiser South Sacramento Medical Center, said many patients are elderly or have persistent conditions. In the past, when they wanted professional advice, they would have to call the advice nurse, who would deliver the question to the doctor.
Now the patient can just e-mail him directly, Kordana said. If he's at his computer, he can respond in under a minute. "It's really freed up my time so I actually have more face-to-face with patients," he said.