Meeting via Craigslist May Boost HIV Rate in High- and Low-Risk Floridians

In the year after Craigslist arrived in communities across Florida, an added 1,149 people became infected with HIV compared with the year before, according to estimates based on a 12-million person analysis. The 13.5% jump in HIV cases reflected new infections in traditionally high-risk as well as lower-risk populations.

Research documents the impact of "Internet-enabled matching platforms" like Craigslist and Grindr on HIV incidence, noted University of Maryland researchers who conducted this study. Their analysis took the next step, figuring how dating-and-mating sites affect incidence in groups defined by gender, race and wealth.

To gauge the impact of Craigslist on HIV rates, the researchers measured the change in HIV incidence before and after Craigslist arrived in individual counties or cities across Florida from January 2002 through December 2006. They used hospital census data involving 12 million people admitted to 223 hospitals in these discrete areas, counting new asymptomatic HIV infections in the year before and the year after local residents could find partners via Craigslist. The analysis took place before other hookup sites, like Grindr and Tinder, became available in these areas.

The researchers determined that asymptomatic HIV incidence in studied populations rose 13.5% after Craigslist's debut. They estimated that an additional 1,149 people picked up HIV in the year after Craigslist arrived than in the preceding year. Blacks accounted for almost two thirds of the new infections, 63%, a surprising finding given research showing slower Internet adoption by blacks than other racial/ethnic groups. The high proportion of newly infected blacks could indicate that non-Internet factors were coincidentally driving HIV incidence higher in blacks during the study period.

HIV incidence also rose among whites and Latinos after Craigslist went online, although those increases were not always statistically significant. The new HIV rate did not differ significantly between whites and Latinos, another surprising finding in light of higher overall HIV prevalence among Latinos than whites in the U.S. Nor did post-Craigslist HIV incidence differ much between men and women (54% and 46% of new infections), even though gay and bisexual men account for the bulk of new U.S. HIV infections. People not using Medicaid accounted for 62% of new HIV infections, a counterintuitive finding given the traditionally higher HIV risk in poorer groups that rely on Medicaid for care.

Together, these findings suggest that a general-population mating platform like Craigslist can have a leveling effect on HIV incidence. "HIV prevention efforts tend to focus on the highest-risk populations, such as the economically disadvantaged," said senior researcher Ritu Agrawal in a press statement, "but public-health officials should be aware that online platforms may be 'changing the game.'"

The University of Maryland team calculated that the additional HIV cases they counted cost Florida an extra $6.9 million in annual treatment costs starting in 2006 and a cumulative additional treatment tally of $710 million over the lifetimes of everyone with new HIV infection.

The analysis is limited by its focus on HIV incidence in people admitted to the hospital; population-wide HIV incidence may be higher or lower if incidence could be measured in both inpatients and non-hospitalized people. Also, the study could not determine how many infected people actually used Craigslist to meet sex partners or even had Internet access. And the researchers could not assess other HIV risk factors beyond race, gender and Medicaid use.

The study, "Matching platforms and HIV incidence," will be published in the journal Management Science.

Mark Mascolini is a freelance writer focused on HIV infection.