Craigslist launched in Boston, Chicago, New York and six other cities in 2000 and expanded into four cities during each of the following two years. In 2003 it moved into a further 14 cities and in 20011 was present in more than 700 local sites in 70 countries.
The researchers tracked the incidence of new cases of AIDS and syphilis in 50 states and the District of Columbia from 1998 to 2005. They concluded that the entry of Craigslist into an area led to a 14 percent increase in the rate of new AIDS cases resulting in more than $US94 million in annual treatment costs and an 18.8 percent increase in the rate of new syphilis cases, leading to annual treatment costs of more than $US0.84 million.
The researchers were able to drill down and find more specific links: The increase in the AIDS rate was influenced by the number of "Men Seeking Men" ads. The increase in the syphilis rate was influenced by both the number of "Men Seeking Women" and "Women Seeking Men" ads.
Principal researcher Anindya Ghose, New York University Stern School of Business Associate Professor of Information, Operations and Management Sciences, said: "Our study results demonstrate that Craigslist, as a minimally regulated online intermediary with no posting costs, increases the number of transactions taking place, including transactions that have undesirable social consequences.
"Despite the known health risks involved, market participants exert little regulation over their casual sex behaviour, resulting in more STD infections and a need for more resources to diagnose and treat infected individuals."
The full paper: "Internet's Dirty Secret: Assessing the Impact of Technology Shocks on the Outbreaks of Sexually Transmitted Diseases," is available here.