Objective: The prevalence of syphilis differs considerably between different populations and individual
level risk factors such as number of sex partners seem unable to completely explain these
differences. The effect of network level factors, such as the prevalence of partner concurrency, on
syphilis prevalence has not hitherto been investigated. Study design: Linear regression was performed
to assess the relationship between the prevalence of male concurrency and prevalence of
syphilis in each of 11 countries for which we could obtain comparable data. The data for concurrency
prevalence was taken from the WHO/Global Programme on AIDS (GPA) sexual behavioural
surveys. Syphilis prevalence rates were obtained from antenatal syphilis serology surveys done in
the same countries. In addition, we used linear regression to assess if there was a relationship
between syphilis and concurrency prevalence of various racial and ethnic groups within the United
States and South Africa. Results: In the international study, we found a strong relationship between
the prevalence of male concurrency and syphilis prevalence (r = 0.79, P = 0.003). In the
subnational studies, the relationship between concurrency and syphilis prevalence was positive in
all cases but was only statistically significant so in the case of South Africa’s racial groups (r = 0.98,
P = 0.01). Conclusions: The findings of an ecological-level association between syphilis and partner
concurrency need to be replicated but suggest that efforts directed towards decreasing partner
concurrency may reduce syphilis prevalence.