(CNN) It's called the "celebrity effect" -- the ability of a well-known personality to raise awareness of an illness or public health concern.

When Katie Couric had a live TV colonoscopy in 2000, screenings and awareness of colon cancer increased. Angelina Jolie's 2013 decision to remove both breasts more than doubled genetic testing referrals among women at high risk for breast cancer.

Now there's the "Charlie Sheen effect." When Sheen announced in November he had been hiding his HIV-positive status for years, media coverage and public interest on the star and the topic of HIV exploded. A study published Monday in JAMA Internal Medicine shows just how much.

Researchers from San Diego State University's School of Public Health ran an analysis of media and Internet searches after Sheen's November 17 announcement. They found that media coverage of HIV on the day of Sheen's disclosure ranked in the top 1% compared with the last seven years. It followed years of declining media coverage of HIV -- from 67 stories per 1,000 in 2004 to 12 stories per 1,000 in 2015.

The actor's announcement was also connected to the most Google searches on HIV ever recorded in the United States, the study said. Using an experimental algorithm to mine data from the day Sheen spoke out to December 8, researchers found 2.75 million more searches than expected contained the word HIV. Perhaps more impressive, researchers said, 1.25 million of those searches "were directly relevant to public health outcomes because they included search terms for condoms, HIV symptoms, or HIV testing."

"That's great news," said Morrigan Phillips, program director for Victory Programs' Boston Living Center , one of 17 health and housing programs that serve the HIV, addiction and homeless population in the Boston area. "People are curious. Hopefully they have found their way to useful and accurate sources of information such as the Centers for Disease Control (and Prevention)."

"The day of Sheen's disclosure was the the biggest abrupt HIV event in our existence," said JD Davids, managing editor of TheBody.com , an HIV/AIDS awareness site founded 25 years ago. "It was our largest traffic day ever, by far. Our usual top traffic day is World AIDS Day, and the day of Sheen's disclosure and the two that followed drastically exceeded that level of activity."

"The sheer volume of searches shows how much interest there is, but it's also an alarm bell," said Carl Sciortino, executive director of the Massachusetts AIDS Action Committee . "There is a lack of information or general awareness."

"We see it every day at AIDS Action when we talk to young people who have never had basic sex education. And we see it every day when someone newly diagnosed walks in our door and is in a panic because they don't know the first thing about HIV."

Sheen as role model?

Two months after Sheen came out of the "HIV closet," he told Dr. Mehmet Oz he had stopped taking the HIV drugs that had reduced the virus to "undetectable levels" in his blood. Instead, he was working with a doctor in Mexico, unlicensed in the United States, who claimed to be developing a cure for HIV.

Sheen then flip-flopped when his manager told People magazine the actor was back on his HIV medications after his viral levels went back up.

Such changes in treatment can put even more pressure on community organizations to provide evidence-based prevention services, but Sciortino said he looks on the bright side.

"HIV thrives in dark places, in silence," he said. "Every year that goes by we have a new generation that doesn't remember the darkest days. Visibility, conversation, press attention are all good for raising awareness, even stories about an actor that causes polarizing reactions."

"It's the Sheen effect, no matter who he is or what he believes or what he does," said Davids, adding that Sheen's disclosure shows "even rich and well-known people are subject to terrifying HIV stigma.

"No one would recommend this guy as an ambassador for feminist, egalitarian relationships. That being said, he can absolutely take a vital leadership role in providing accurate and lifesaving information on HIV, and in advocating for the policies that can end the epidemic in our lifetimes."

The good and bad of the 'celebrity effect'

The role of celebrities in bringing attention to little-discussed diseases can be huge. Michael J. Fox put a human face on Parkinson's disease and raised millions to search for a cure. Lance Armstrong made it OK to talk about testicular cancer and the need for young men to be screened. Montel Williams frequently talked about his personal battle with multiple sclerosis on his talk show. And while social media deserves the real credit for the success of the ALS Ice Bucket Challenge, mass celebrity participation certainly played a key role in driving the $115 million in donations.

But while Couric, Fox and Williams seem to have improved the public's awareness of devastating diseases, some celebrities have sent out messages that run counter to mainstream medical advice.

Michael Parkinson, a British broadcaster diagnosed with prostate cancer, told the public how men could determine if they too had the disease. "The test is if you can pee against a wall from 2 feet, you haven't got it," Parkinson said. The medical community was quick to refute his claim.

In the States, actor Suzanne Somers promotes proteolytic enzyme therapy for pancreatic cancer and bioidentical hormones to reverse aging despite little scientific proof for either.

And then there are the many celebrities who have come out publicly against childhood vaccinations. Alicia Silverstone expressed her anti-vax views in her 2014 book, "The Kind Mama." In 2012 and again in 2015 Donald Trump linked them to autism, something medical science has refuted again and again. GOP candidates Ron Paul and Ben Carson did the same.

Long before that, Jenny McCarthy became the face of the anti-vaccination movement, which she blamed for years for her son's autism. In an article for The Huffington Post in 2009, McCarthy's ex, actor Jim Carrey, said, "In this growing crisis, we cannot afford to blindly trumpet the agenda of the CDC, the American Academy of Pediatrics or vaccine makers."

The 'Angelina effect'

Over the years, researchers have been studying the celebrity effect to help organizations maximize public health benefits and reduce potential negatives.

Angelina Jolie decided to undergo a double mastectomy in 2013.

One case that has been studied in depth is Jolie's 2013 decision to undergo a double mastectomy because she inherited the BRCA1 gene, putting her at high risk for breast and ovarian cancer. A UK study found referrals to genetic testing among high-risk Englishwomen rose by 2.5% in the two months after her announcement, a ripple effect that lasted another three months before it began to fade. The same researchers continued to analyze numbers throughout 2014 and into 2015, and found women still mentioning the "Angelina effect" as a reason for their doctor visits and questions about potential risk.

Not only did her action send more Englishwomen to their doctors, the researchers said, but 2.5% more women choose to undergo a bilateral risk-reducing mastectomy.

In the United States, researchers found Jolie's revelation had a similar impact on public awareness and Internet use as Sheen's, showing a massive increase in traffic to the National Cancer Institute's online resources.

But there was also a downside. Researchers also found that while three of every four Americans knew about Jolie's actions, "fewer than 10% of respondents had the information necessary to accurately interpret Ms. Jolie's risk of developing cancer relative to a woman unaffected by the BRCA gene mutation," the authors said. They concluded that public awareness in this case was "not associated with improved understanding."

An analysis in the BMJ concluded: "Jolie's announcement may have catalyzed a herd seeking the test, including many for whom it is neither appropriate nor cost effective."

'We could save a lot of lives'

The bottom line, according to experts: While no one disputes the benefit of well-crafted, medically accurate celebrity messages, the medical community needs to up its communication efforts so that members of the public can better understand the information to improve their health.

Join the conversation See the latest news and share your comments with CNN Health on Facebook and Twitter.

"In the era of social media and 24-hour news cycle, it's easy for things to be sensationalized and then forgotten," said Phillips of the Victory Programs' Boston Living Center. In the case of Sheen and his impact on HIV prevention, she added, more needs to be done.

"This cannot just be a flash in the pan," she said. "HIV prevention and treatment is larger than this moment."

Sciortino adds, "Charlie himself has a real opportunity to do some good. We would all benefit if he would work with public health organizations to figure out the right message and story to put out there.

"For example, most of the world still doesn't know that we now have a pill a day that prevents HIV, pre-exposure prophylaxis (PrEP). If Charlie got that story out there, we could save a lot of lives."