Human immunodeficiency virus infection can lead to AIDS, which affects 1.2 million Americans, according to the U.S. Centers for Disease Control and Prevention. Sheen's announcement, which made national headlines, renewed attention to the dangers of HIV and AIDS at the time.
According to the study update, what it called the "Charlie Sheen effect" had a big impact on HIV testing in the U.S., with sales of at-home testing nearly doubling the week of his announcement.
Researchers from the University of Southern California and the University of California at San Diego, among other institutions, published their findings today in the medical journal Prevention Science. The study was a follow-up to one published last year, which documented a surge in people searching for information on HIV and AIDS.
"Our strategy allowed us to provide a real-world estimation of the Charlie Sheen effect on HIV prevention and contrast that effect with our past formative assessment using Internet searches," study co-author Eric Leas, a research associate in the San Diego State University–UCSD doctoral program in public health, said in statement today.
The researchers looked at weekly sales data from April 12, 2014, to April 16, 2016, of OraQuick rapid in-home HIV tests, the only test of this type available in the U.S. They found that the week after Sheen announced on the "Today" show that he was HIV positive, in November 2015, there was a 95 percent increase in OraQuick HIV test sales.
The HIV test sales continued to be above normal over the next four weeks, fluctuating from approximately 20 percent to 60 percent above the previous level.
Surprisingly, researchers found that these numbers far surpassed the sales uptick after World AIDS Day. Despite widespread attention to encourage people to get tested or be HIV aware through the World AIDS Day campaign, they found that sales increased just 31 percent but that rates returned to normal the next week.
Testing is key to combating HIV, since symptoms of infection often do not appear for years. According to the CDC, 1 in 8 of those infected in the U.S. is not aware of having the virus.
John Ayers, a behavioral scientist at SDSU, said the study could help public health officials better engage with people.
"We can make public health more connected to the public it serves," he told ABC News. According to him, the public health system is top-down, and informational messages come mainly from experts. "We forgot to listen to the public, and this is what the public is engaging on."
Ayers and his team also looked at how search terms on Google trends were associated with increased sales and found they could predict sales within a somewhat small margin of error.
"We can discover when events are occurring, measure their impact and work to grow their impact," he said. "That's what public health can become."
The case shows it is key for public health officials to take advantage of these public announcements, according to Dr. Barron Lerner, a professor of medicine and population health at NYU Langone Medical Center.
"People look down at celebrities and feel that the information that's being generated is not useful to regular people," Lerner said. "But it reminds us that, regardless of who the person is, it will at least generate interest."
Ayers had a similar take. "It's an empowering message. The truth is that you can make a difference by just speaking out on something," he said. "We all hear talk is cheap. That's not true."
Lerner said that Sheen's talking about his high-risk sexual practices may have also helped educate people about risks surrounding HIV, which is primarily spread through sexual contact and intravenous drug use. Additionally, Lerner said, more people getting tested for HIV is "a good thing, regardless of who he is."
Dr. Crystal Tan contributed to this article. She is an anesthesiology resident at Massachusetts General Hospital and part of the ABC News medical unit.