Getting to the bottom of it: Sexual positioning and stage of syphilis at diagnosis, and implications for syphilis screening.Clin Infect Dis. 2019 Aug 17 [Online ahead of print]CI
Syphilis control among 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 the duration of infectivity. We hypothesised that men who have sex with men (MSM) who practised receptive anal intercourse were more likely to present with secondary syphilis, compared to MSM who did not practise receptive anal intercourse.
In this retrospective analysis of MSM diagnosed with primary or secondary syphilis at Melbourne Sexual Health Centre between 2008 and 2017, we analysed associations between the stage of syphilis (primary vs secondary) and behavioural data collected by computer-assisted self-interview (CASI).
559 MSM were diagnosed with primary (n=338) or secondary (n=221) syphilis. 134 (24%) men reported not practising receptive anal sex. In multivariate logistic regression, MSM were more likely to present with secondary rather than primary syphilis if they reported practising receptive anal intercourse (adjusted odds ratio 3.90, p<0.001) after adjusting for age, HIV status, and condom use. MSM with primary syphilis who did not practise receptive anal intercourse almost always (92%) had their primary syphilis lesion on their penis.
The finding that MSM who practised receptive anal intercourse more commonly presented with secondary syphilis, and hence in whom the primary stage had gone undetected, 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.