In this paper I leveraged recent variation in access to same-sex marriage across states and time to test the competing hypotheses that legal same-sex marriage either increased or decreased the incidences of syphilis, gonorrhea, and chlamydia in a quasi-experimental framework. Results reveal a strong and significant association between the legalization of same-sex marriage and reductions in syphilis rates, an exceptionally strong proxy of risky sex between men. This finding appears to be driven largely by men and young adults. Results also suggest, to a lesser extent, an association between legal same-sex marriage and reductions in chlamydia rates, a more diluted signal of risky sex between men.
I find little evidence of a relationship between same-sex marriage and rates of gonorrhea.
The null finding for gonorrhea, though consistent with Dee (2008) and Francis et al. (2012), raises the question: why would the legalization of same-sex marriage impact rates of syphilis and chlamydia but not gonorrhea, especially given that MSM almost certainly constitute a larger portion of gonorrhea cases
than chlamydia cases (see Figure 1.3)? The answer may have something to do with the timing and severity of symptoms presented by each STI. While gonorrhea can be asymptomatic (Peterman et al., 2006), symptoms in men usually appear one to fourteen days after becoming infected (Harrison et al., 1979), and include discharges from the infected area, itching, and soreness. Symptoms of syphilis, on the other hand, can take anywhere from ten days to three months to manifest, and begin with the appearance of a single sore lasting three to six weeks (CDC, 2017c). These sores often go unnoticed as they are typically painless and can be located in areas that are difficult to see. Even more likely to go unnoticed is chlamydia, which is usually asymptomatic, manifesting symptoms in only an estimated 6 to 30 percent of infected women and 11 percent of infected men (Korenromp et al., 2002; Farley et al., 2003). Even in those cases where symptoms of chlamydia do manifest, it is not until several weeks after infection (CDC, 2017b). In other words, it is much more difficult for someone to be unaware that they have been infected with gonorrhea than it is to unknowingly be infected by syphilis or chlamydia, meaning syphilis and chlamydia are more likely to be discovered by precautionary screening than gonorrhea. The findings that same-sex marriage is associated with reductions in syphilis and chlamydia but not gonorrhea are consistent with the hypothesis that the legalization of same- sex marriage induced sexual minorities to care more about whether or not they are unknowingly carrying an STI, perhaps because sexual health is valuable in the
new LGB marriage market or because sexual minorities are now more invested in the health of their partners. Either way, if individuals are more likely to seek STI screening after the legalization of same-sex marriage, then cases of infections with few or delayed symptoms, such as syphilis or chlamydia, are sure to be identified and treated earlier than they would have been otherwise, thereby shortening the window during which infected individuals are unknowingly spreading these infections.
An analysis using Google Trends data returned evidence of an increase in internet searches relating to syphilis and chlamydia in men and treatment for syphilis after the legalization of same-sex marriage. This is also consistent with the hypothesis that legalizing same-sex marriage induced MSM to seek more frequent screening for syphilis and chlamydia. While increased screening has the effect of limiting the spread of an STI, it is also likely to catch some cases that would have gone unreported otherwise. Such cases would not have shown up in the NNDSS data prior to same-sex marriage, and would therefore bias the estimated effect of legal same-sex marriage on STIs towards zero. Nonetheless, a conservative back of the envelope calculation using the coefficient from the top panel of column 1 in Table 1.1 implies that legal same-sex marriage prevents 3,895 new cases of syphilis each year. Using the cost per syphilis case estimated by Owusu-Edusei et al. (2013), 3,895 fewer syphilis cases each year equates to annual savings of roughly $3.2 million (2018 dollars) in direct syphilis related
medical expenditures. The coefficient in column 1 of panel 3 in Table 1.1 implies a reduction of 76,044 new cases of chlamydia each year. A similar calculation including reductions in chlamydia yields total annual savings in excess of $5.8 million (2018 dollars).19 Overall the findings of this paper suggest that the legalization of same-sex marriage likely had the unintended consequence of improving public health with respect to sexually transmitted infections, improving the quality of life among sexual minorities and saving $5.8 million in direct costs every year. Relatedly, these findings suggest that efforts to repeal same-sex marriage, if successful, may negatively impact public health.
19 Owusu-Edusei et al. (2013) estimates that the lifetime cost of a case of syphilis is $709 in 2010 dollars. They estimate that a case of chlamydia carries a lifetime cost of $30 for a man and $364 for a woman in 2010 dollars.