Keywords. China; HIV; syphilis.The story of sexually transmitted diseases(STDs) in China is complicated andcompelling [1]. Before the formation ofthe People’s Republic of China (PRC) in1949, sexually transmitted infectionswere a major source of disease [2]. Forexample, in 1949, 84% of sex workers inBeijingwereestimatedtohavesyphilis[3].In this same year 10% of all infants bornat Beijing Medical College suffered fromcongenital syphilis, and among some ofChina’s national minority groups syphilisprevalence exceeded 50% [4]. In the faceof this staggering burden of disease, theearly leaders of the PRC prioritizedpublic health. By 1964, extraordinary na-tional initiatives had virtually eliminatedsyphilis [1].But syphilis and other STDs have re-turned to China with a vengeance [5, 6].China now faces a substantial burden ofSTDs in the general population [7–9],and alarmingly high prevalence of STDsamong at-risk populations including sexworkers and men who have sex with men(MSM) [10–12]. Recognizing the gravityof the problem, in 1987, the governmentdeveloped a mandatory case reportingsystem [8]. Between 2004 and 2011, thisnational sentinel surveillance system re-corded a >4-fold increase in syphiliscases [5]. In 2011, China’s syphilis inci-dence of 32.0 new cases per 100000 resi-dents [5] stood in sharp contrast tosyphilis incidence in the United States(4.5 new cases per 100000) [13] andEngland (5.6 newcases per 100000)[14].How can we explain this rapid resur-gence of STDs? China’s unprecedentedsocial, political, and economic changesbeginning in the 1980s favor the trans-mission of STDs [15, 16]. Earlier sexualdebut, later marriage, more lifetime part-ners, and more commercial sex [17–19]have vastly accelerated the spread ofSTDs. Population-level biological forcesmay also play a role. Following syphilisinfection, the immune system registers amemory response that could result inheightened immunity or alter the courseof disease [20]. Grassly et al demonstrat-ed the plausible impact of this responseleading to herd immunity though a mod-eling study of syphilis trends in theUnited States [21]. If their argument iscorrect, the great success of China’searlier eradication campaigns may havede facto led to heightened susceptibilityacross a general population with virtuallyno immune experience with syphilis forseveral generations.Globally, it has become clear that thespread of STDs and human immunodefi-ciency virus (HIV) among MSM deservesintense attention [22]. In this issue ofClinical Infectious Diseases, Wu and col-leagues describe a remarkable nationalstudy of HIV and syphilis prevalenceamong MSM in China. The investigatorsconducted a61-city,cross-sectionalstudyof >47000 MSM. The results are sober-ing. The prevalence of HIV infection inthe population surveyed was 4.9% andthe prevalence of syphilis infection was11.8%. This disease prevalence is consis-tent with reports of the spread of syphilisand the disproportionate burden of HIVamong MSM worldwide [23].At the patient level, Wu et al’sdatareflect the fierce synergy between HIVand syphilis. Among those with syphilisinfection, HIV prevalence was >3 timeshigher (3.9% vs 12.5%). Importantly,syphilis measurement assessed activeor recent infection rather than lifetimeexposure. This critical distinction sup-ports the link between ulcerative STDsand heightened susceptibility to HIVinfection [24].Examination of the ecological andpopulation-level results is more compli-cated. The investigators chose particular