Getting to the Bottom of It: Sexual Positioning and Stage of Syphilis at Diagnosis, and Implications for Syphilis Screening

Background. Syphilis control among men who have sex with men (MSM) would be improved if we could increase the proportion of cases who present for treatment at the primary stage rather than at a later stage, as this would reduce their duration of infectivity. We hypothesized that MSM who practiced receptive anal intercourse were more likely to present with secondary syphilis, compared to MSM who did not practice receptive anal intercourse. Methods. In this retrospective analysis of MSM diagnosed with primary or secondary syphilis at Melbourne Sexual Health Centre between 2008 and 2017, we analyzed associations between the stage of syphilis (primary vs secondary) and behavioral data collected by computer-assisted self-interviews. Results. There were 559 MSM diagnosed with primary (n = 338) or secondary (n = 221) syphilis. Of these, 134 (24%) men reported not practicing receptive anal sex. In multivariable logistic regression analysis, MSM were more likely to present with secondary rather than primary syphilis if they reported practicing receptive anal intercourse (adjusted odds ratio 3.90; P < .001) after adjusting for age, human immunodeficiency virus status, and condom use. MSM with primary syphilis who did not practice receptive anal intercourse almost always (92%) had their primary syphilis lesion on their penis. Conclusions. The finding that MSM who practiced receptive anal intercourse more commonly presented with secondary syphilis-and hence, had undetected syphilis during the primary stage-implies that anorectal syphilis chancres are less noticeable than penile chancres. These men may need additional strategies to improve early detection of anorectal chancres, to reduce their duration of infectivity and, hence, reduce onward transmission.