Hookups via the online ad website Craigslist have been linked to an increase in cases of HIV, researchers from New York University and the University of Minnesota have found.

Researchers concluded there was a nearly 16 percent increase in HIV cases across U.S. cities after Craigslist became available in the area, according to the New York Daily News.

The increase was attributed to those who cruised the site's personal ads looking for sexual encounters, said study co-author Jason Chan, assistant professor of information and decision sciences at the University of Minnesota.

Chan, who conducted the study with NYU professor Anindya Ghose, was working on his dissertation about the social and health effects of Internet platforms when he got the idea to take a look at Craigslist, the Star Tribune reported.

"We started seeing a lot of ads for these personal hookups and one night stands," Chan told the Daily News. "We were originally under the impression that maybe it was just a New York City thing."

The duo looked at 33 cities from 1999 and 2008. In every city, there were increases of HIV cases a year after Craigslist arrived- a delay caused by how long it took for the site to gain followers and for symptoms to appear in those infected.

There were an additional 6,000 HIV cases a year during the time period studied, resulting in an estimated $62 million to $65.3 million for treatment costs.

Chan and Ghose found no differentiation between types personal ads, such as men seeking women or men seeking men. Their findings were published in the journal MIS Quarterly.

"Our study results suggest that there is a new social route of HIV transmission that is taking place in this digital era," Chan said. "Health care practitioners and policymakers have to look more closely at online platforms to assess how its usage may facilitate the spread of HIV and STDs across the country."

Already thinking ahead of Craigslist, some researchers are looking into the impact of cellphone apps for dating that lead to almost instant hookups wherever the person is.

Paige Padgett, a University of Texas assistant professor studying interaction via mobile apps, said one of the problems with apps, and perhaps dating sites, is they can lead to a false sense of intimacy.

"You're sharing personal information a lot faster...so then when you actually meet face to face, you feel you really know that person," she told the Star Tribune.