Syphilis Cases Plummet in Hangzhou District After Two-Decade Epidemic Peak

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The two-decade record from Xihu District offers an unusually granular window into how a mature urban syphilis epidemic can bend downward when surveillance, treatment, and screening programs operate continuously over a generation. The inverted U-shaped trajectory documented in the study—climbing from 68.71 reported cases per 100,000 residents in 2005 to a peak of 155.16 per 100,000 in 2010, then falling to just 13.17 per 100,000 by 2025—mirrors in miniature the broader arc of China’s syphilis resurgence and subsequent response. When the national epidemic re-emerged in the late 1990s after near-elimination, coastal provinces with dense populations, high mobility, and strong healthcare infrastructure were among the first to register steep increases. Zhejiang Province, and Hangzhou in particular, fit that profile precisely, which helps explain why Xihu District was classified as a hyperendemic area for local transmission and why its reported incidence long exceeded national averages.

The joinpoint analysis identifying four distinct phases adds interpretive value beyond what a simple linear trend could convey. The rapid growth phase from 2005 to 2008, with an annual percentage change of 25.23 percent, likely reflects a combination of genuine transmission intensity and expanding case-finding capacity. The China Information System for Disease Control and Prevention, launched nationally after the 2003 SARS epidemic, mandated that hospitals, community health centers, and township facilities report confirmed syphilis cases within 24 hours of diagnosis. As this real-time reporting infrastructure matured in the mid-2000s, previously uncounted cases would have entered the system, inflating apparent incidence even before any true change in transmission. Disentangling ascertainment effects from genuine epidemiological shifts is a perennial challenge in interpreting notifiable disease data, and the authors’ reliance on a single passive surveillance source means some caution is warranted when attributing every inflection point to changes in disease dynamics alone.

The mild decline phase from 2008 to 2019, with an annual percentage change of negative 5.00 percent, coincides with a period in which China scaled up syphilis screening in antenatal clinics, expanded free treatment policies, and integrated sexually transmitted infection services into broader HIV prevention frameworks. The accelerated decline from 2019 to 2023, at negative 18.69 percent annually, and the apparent reduction phase from 2023 to 2025, at negative 39.01 percent annually, are striking in their steepness. Part of this acceleration plausibly reflects genuine programmatic success, including expanded provider-initiated testing and partner services. However, the timing also overlaps with the COVID-19 pandemic and its aftermath, during which healthcare-seeking behavior, screening volumes, and reporting practices were disrupted across China and globally. Reduced opportunistic screening during lockdown periods and altered healthcare utilization patterns could suppress reported incidence independently of true transmission declines. The authors acknowledge residual challenges such as hidden undiagnosed latent infections, and the extraordinarily steep final-phase decline should be read with this measurement context in mind.

The dominance of latent syphilis across all stages and throughout the entire study period deserves particular emphasis. Latent syphilis is defined by the absence of clinical symptoms despite serological evidence of infection, and it is detected almost exclusively through screening rather than symptomatic presentation. A high proportion of latent cases in surveillance data can indicate two very different realities: either widespread successful case-finding that captures asymptomatic infections before they progress, or a large reservoir of undiagnosed infection circulating silently in the population. Because latent syphilis can still be transmitted vertically from mother to fetus and can reactivate or progress to tertiary disease, the persistent latent predominance in Xihu District suggests that screening intensity, not just symptomatic care, drove much of the observed epidemiology. The steep decline in primary and secondary syphilis, with average annual percentage changes of negative 14.76 percent and negative 12.19 percent respectively, is more directly interpretable as a reduction in recently acquired infections, since these stages manifest with characteristic lesions that prompt clinical presentation.

The near-disappearance of congenital syphilis is among the most consequential findings for public health practice. The surge in congenital cases during 2006 and 2007 aligns with the tail end of the national epidemic’s growth phase, when maternal infection prevalence was high and routine antenatal syphilis screening was not yet universal. China subsequently made antenatal syphilis testing a standard component of prenatal care and, in 2010s policy iterations, provided free screening and treatment for pregnant women. The fact that no notified congenital syphilis cases have been recorded in Xihu District since 2017 represents achievement of a milestone that the World Health Organization’s global strategy frames as central to elimination efforts. The WHO targets for 2030 include reducing adult syphilis incidence by 90 percent relative to a 2020 baseline and keeping congenital syphilis below 50 cases per 100,000 live births. Xihu District’s congenital notification rate of zero for eight consecutive years exceeds that threshold by a wide margin, though maintaining elimination requires sustained vigilance, since congenital syphilis can re-emerge quickly if antenatal screening coverage lapses.

The gender disparity in decline rates, with females showing an average annual percentage change of negative 10.23 percent compared with negative 5.54 percent among males, is consistent with patterns observed in many syphilis control programs. Women are more likely to encounter the healthcare system through reproductive health services, antenatal visits, and gynecological care, creating additional screening touchpoints that men typically lack. This structural asymmetry in healthcare contact means that male-focused outreach, including services delivered through venues frequented by men who have sex with men, migrant worker populations, and other groups with limited routine care engagement, remains essential for closing the gap. The faster decline among women also compounds the significance of the congenital syphilis elimination, since reduced maternal infection directly protects pregnancies.

The age-stratified findings highlight two populations requiring continued attention. Adults aged 20 to 39 consistently carried the highest reported incidence burden, with a long-term average annual percentage change of negative 10.47 percent. This age concentration reflects peak sexual activity years and aligns with national Chinese data showing syphilis incidence rising among adolescents and young adults even as overall trends improved. Interventions tailored to this group, including digital outreach, youth-friendly clinic services, and integration with HIV pre-exposure prophylaxis programs, are logical priorities. The elderly population aged 60 and above presented a different pattern: prominent high reported incidence before 2019 followed by a sharp drop, with an average annual percentage change of negative 9.53 percent. Elevated syphilis rates among older adults in China have been attributed in part to widespread opportunistic screening during hospital admissions and health examinations, which can detect long-standing latent infections, as well as to genuine transmission within this age group. The post-2019 decline among the elderly may partly reflect changes in screening practices during the pandemic era, again underscoring the need to distinguish reported incidence from true incidence.

Tertiary syphilis remained at extremely low absolute levels with sparse case counts throughout the 21 years, which is expected given that tertiary disease develops years to decades after initial infection and requires prolonged untreated latency. The rarity of tertiary cases in the surveillance record suggests either effective interruption of progression through earlier detection or under-ascertainment of late manifestations that present to cardiology, neurology, or ophthalmology services without syphilis serology being ordered. Sparse counts also limit statistical power for trend estimation in this subgroup, a limitation inherent to analyzing rare outcomes.

Several methodological considerations frame the interpretation of these findings. The study uses reported rather than confirmed incidence, meaning case counts depend on diagnostic criteria, testing frequency, and reporting compliance, all of which changed over the study window. Diagnostic classification shifted from the GB 15974-1995 standard to WS 273-2007 in 2007 and then to WS 273-2018 in 2018, and such criteria revisions can introduce artificial discontinuities in staged case counts. Population denominators drawn from municipal statistical bureau estimates may not fully capture the massive migrant population flowing through Xihu District, potentially distorting rate calculations in either direction. Joinpoint regression, while powerful for identifying inflection points, can be sensitive to the number of allowed joinpoints and to short-term fluctuations, particularly in the final 2023 to 2025 segment where only a few data points drive the steep negative 39.01 percent estimate.

Despite these caveats, the overall picture is one of substantial, sustained progress. A decline from a peak of 155.16 per 100,000 to 13.17 per 100,000 over fifteen years represents roughly a 92 percent reduction from the epidemic’s height, approaching the scale of reduction the WHO envisions globally by 2030. For a district once classified as hyperendemic, this trajectory demonstrates that comprehensive, long-duration control programs combining surveillance, universal antenatal screening, accessible treatment, and targeted outreach can fundamentally reshape local syphilis epidemiology. The residual challenges the authors identify—persistent vulnerability among young adults and the elderly, and the hidden burden of undiagnosed latent infection—define the agenda for the next phase of control, in which the final mile toward elimination will likely prove more demanding than the steep initial decline. Lessons from Xihu District are relevant beyond Zhejiang, offering a template for other high-burden urban districts navigating the transition from epidemic containment to elimination-level targets.

Subject of Research: Epidemiological trends of reported syphilis incidence in Xihu district, Hangzhou, China, 2005–2025

Article Title: Epidemiological trends of reported syphilis incidence in Xihu district, Hangzhou, China, 2005–2025

Article References: Li, J., He, L., Wu, T., Meng, J., Wang, T., Sun, F., & Wang, B. (2026). Epidemiological trends of reported syphilis incidence in Xihu district, Hangzhou, China, 2005–2025. Frontiers in Epidemiology, 6, Article 1944790. https://doi.org/10.3389/fepid.2026.1944790

Image Credits: AI Generated

DOI: 10.3389/fepid.2026.1944790

Keywords: Epidemiological, trends, reported, syphilis, incidence, Xihu, district, Hangzhou, China, scientific research