HIV-positive actor Charlie Sheen has helped increase awareness and testing of the condition according to two new U.S. studies looking into what researchers have dubbed the "Charlie Sheen effect."

The first study, led by San Diego State University Graduate School of Public Health research professor John W. Ayers, found that millions of online search queries for HIV prevention and testing were carried out after the actor made the announcement that he is HIV-positive on NBC's "Today Show" on Nov. 17, 2015.

In a more recent follow-up study, also by Prof Ayers, the team investigated whether internet search queries, which they based on Google Trends data on searches with "test," "tests," or "testing" and "HIV," showed a link with an increase in HIV testing.

The researchers collected data on sales of OraQuick, the only rapid at-home HIV test kit available in the United States, and found that in the same week Sheen made his TV appearance, sales in OraQuick nearly doubled, reaching an all-time high.

Sales continued to remain significantly higher than usual for the following three weeks, with 8,225 more sales than expected.

"In absolute terms, it's hard to appreciate the magnitude of Sheen's disclosure," commented study co-author Benjamin Althouse, "However, when we compared Sheen's disclosure to other traditional awareness campaigns the 'Charlie Sheen effect' is astonishing."

One of the most high-profile and longest-running of these traditional awareness campaigns is World AIDS Day, with OraQuick sales following Sheen's announcement nearly eight times greater than sales around the well-known event.

Study co-author Mark Dredze, a Johns Hopkins University computer scientist, added that "public health must ready itself for the next Sheen-like event by embracing big media data for decision making." However, he also added that the Charlie Sheen effect may still be going.

"Our findings build on earlier studies that suggest empathy is easier to motivate others when the empathy is targeted toward an individual versus a group," explained co-author Jon-Patrick Allem, research scientist with the University of Southern California Keck School of Medicine.

"It is easy to imagine that a single individual, like Sheen, disclosing his HIV status may be more compelling and motivating for people than an unnamed mass of individuals or a lecture from public health leaders."

The findings can be found published online in the journal Prevention Science.