Hepatitis B and C in Hainan: reported incidence trends diverge from national estimates and forecasts reveal persistent hepatitis C gap

On the tropical island province of Hainan, China’s only province of this kind and one of its most visited international tourism destinations, the reported incidence of hepatitis B and hepatitis C has followed trajectories that stand in sharp contrast to the national picture. A new time-series analysis published in Frontiers in Epidemiology has now dissected sixteen years of surveillance data, from 2005 to 2020, using segmented trend regression, seasonal decomposition, and forecasting models to ask where the province’s reported viral hepatitis burden is heading. The answer is nuanced: hepatitis B reporting rose over much of the study period even as national estimates declined, hepatitis C reporting surged before 2015 and then fell, and neither virus showed a meaningful seasonal rhythm. The authors, led by Jiao Wang and Shibing Li of the Hainan Affiliated Hospital of Hainan Medical University, with Yuanyuan Tian and Cheng Lan as corresponding authors, emphasize that their projections describe the continuation of historical reporting patterns rather than progress toward the World Health Organization’s elimination goals.

The study drew on monthly and annual reported case counts from China’s Public Health Science Data Center, covering 192 consecutive monthly observations for each virus from January 2005 to December 2020. Reported incidence was calculated as cases per 100,000 permanent residents, using year-end population figures from the Hainan Provincial Bureau of Statistics as the denominator. To place the provincial data in context, the team also extracted national Global Burden of Disease (GBD) estimates for China spanning 1990 to 2023, and they obtained annual tourist visit statistics from the provincial tourism department. No missing or duplicate observations were identified, and no study years were excluded, giving the analysis a complete and unbroken record.

Joinpoint regression, a technique that identifies inflection points in a time series and estimates the annual percent change (APC) within each segment, revealed a distinctly phased pattern for reported hepatitis B incidence in Hainan. Rates fell from 2005 to 2008 with an APC of −9.10 percent per year, rose from 2008 to 2018 with an APC of +10.50 percent per year, and then showed a non-significant decline through 2020. Across the full sixteen years, the average annual percent change (AAPC) was +3.37 percent, a statistically significant overall increase. Reported hepatitis C followed a different course: it climbed continuously from 2005 to 2015 at a striking +32.10 percent per year, then declined at −10.90 percent per year through 2020, yielding an overall AAPC of +14.54 percent. By contrast, the national GBD estimates showed overall AAPCs of −0.54 percent for hepatitis B and −1.52 percent for hepatitis C, both modestly downward over their respective periods.

The divergence between provincial reported data and national modeled estimates is a central finding. The authors caution that the two data sources differ in definition and origin, so national GBD trends serve only as contextual references. Still, the mid-period rise in reported hepatitis B in Hainan is unlikely to reflect a simple failure of vaccination strategy. China added hepatitis B vaccination to its childhood immunization program decades ago, and studies from Guangzhou and Xiamen have documented declining reported incidence in those cities. The Hainan increase may instead reflect expanded screening, greater detection of previously acquired chronic infections, repeated healthcare encounters, rising healthcare accessibility, and changes in reporting-system sensitivity, layered on top of genuine transmission dynamics and increasing vaccine-derived protection in younger birth cohorts. China continues to carry a large reservoir of chronic hepatitis B infection, and insufficient diagnosis, treatment, and follow-up remain major barriers to elimination.

For hepatitis C, the pre-2015 surge in reported incidence plausibly mirrors improvements in testing capacity, strengthening of the reporting infrastructure, and increased screening that uncovered previously undiagnosed infections. The post-2015 decline coincided with broader gains in blood safety, awareness, screening, and access to antiviral therapy, including the transformative arrival of direct-acting antivirals (DAAs), which can cure chronic hepatitis C infection in most treated patients. Yet the authors note that Hainan-specific information on testing and treatment coverage was unavailable, so the analysis cannot determine whether these factors caused the observed decline. A large pool of undiagnosed infections may continue to limit progress, since DAAs alone cannot reach patients who are never screened or linked to care.

Seasonality, often a signature of environmentally driven pathogens, was conspicuously absent for both viruses. The team applied seasonal-trend decomposition using Loess (STL), an additive method that splits each monthly series into trend, seasonal, and remainder components with a twelve-month seasonal period. Kruskal–Wallis tests comparing the distributions of the STL seasonal components across calendar months found no statistically significant differences for hepatitis B (H = 11.10, P = 0.435) or hepatitis C (H = 2.81, P = 0.993). Descriptive seasonality indices were highest in July for hepatitis B (107.8) and April for hepatitis C (107.4), and lowest in February for both (78.3 and 73.9, respectively). The February trough may relate to reduced healthcare seeking and delayed testing during the Spring Festival holiday, but the authors stress that these fluctuations likely reflect reporting variation rather than seasonal transmission, and that long-term trends and population-structure changes carry greater public health relevance than isolated monthly peaks.

To project future trajectories, the researchers fitted seasonal autoregressive integrated moving average (SARIMA) models to the monthly series. For hepatitis B, the selected model was SARIMA (0,1,2) × (2,1,0) with a twelve-month seasonal cycle, which had the lowest Akaike information criterion among candidates and passed the Ljung–Box residual autocorrelation test at lag 12 (Q = 10.771, P = 0.549). For hepatitis C, SARIMA (1,1,1) × (0,0,1) was chosen because an alternative with slightly lower information criteria retained significant residual autocorrelation; the selected model showed acceptable diagnostics at lag 24 (Q = 31.162, P = 0.074). Forecasting to 2030, the annualized projected reported hepatitis B incidence was 12.00 per 100,000 population, with a 95 percent prediction interval spanning roughly 0.00 to 121.20, numerically close to the study-defined reference value of 12.20. The hepatitis C projection was 22.54 per 100,000 (approximately 0.00 to 39.10), about 6.4 times the study-defined reference value of 3.55. The reference values were defined as 10 percent of the corresponding 2015 reported incidence rates, echoing the WHO framework of a 90 percent reduction in new infections by 2030, but the authors insist they are not equivalent to WHO elimination targets.

The wide prediction intervals, generated from 10,000 simulated forecast paths, signal substantial long-term uncertainty, and the authors repeatedly warn that the projections are conditional extrapolations of historical reporting patterns. A declining trend, they note, does not necessarily imply proximity to elimination. Hepatitis B control depends on sustained immunization coverage, prevention of mother-to-child transmission, adult diagnosis and treatment, and management of chronic infection, whereas hepatitis C elimination hinges on active screening, rapid linkage to treatment after diagnosis, and improved treatment coverage. Insufficient screening, incomplete linkage to care, declining treatment uptake, and ongoing transmission in high-risk populations may all weaken control efforts even in the DAA era.

Sensitivity analyses highlighted the disruptive fingerprint of the COVID-19 pandemic year. When Joinpoint models were refitted excluding 2020, the overall AAPC rose from 3.37 to 4.96 percent per year for hepatitis B and from 14.54 to 16.43 percent per year for hepatitis C, indicating that the 2020 observations deviated from prior reporting patterns and pulled the long-term trend estimates downward. Out-of-sample SARIMA forecasts built on 2005–2019 data predicted a mean monthly reported hepatitis B incidence of 15.11 per 100,000 for 2020, but the observed value was 10.98, some 27.3 percent lower; for hepatitis C, the forecast of 1.92 exceeded the observed 1.74 by 9.5 percent. Reduced healthcare seeking, testing, and reporting during pandemic-control measures, consistent with findings from China, Spain, and Italy, likely explain these shortfalls rather than any sudden improvement in prevention.

Finally, the study explored ecological associations between annual tourist visits, which grew from roughly 17 million in 2005 to about 83 million in 2019 before falling to approximately 56 million in 2020, and reported hepatitis incidence. In raw annual analyses, tourist visits correlated strongly with both reported hepatitis B (r = 0.871) and hepatitis C (r = 0.879), both P < 0.001, and the associations persisted after excluding 2020. However, because both series shared pronounced long-term trends, the team repeated the correlations on first-differenced and linearly detrended data. Only the hepatitis B association survived (r = 0.567 after differencing, P = 0.028; r = 0.691 after detrending, P = 0.003), while the hepatitis C association vanished (r = 0.070, P = 0.804 after differencing). The authors interpret this cautiously: tourism volume may reflect concurrent changes in population mobility, healthcare use, screening activity, socioeconomic development, and reporting capacity rather than any direct causal effect on transmission. The analyses were aggregated and exploratory, lacking individual-level data on age, sex, vaccination status, transmission route, testing, and treatment. The authors conclude that Hainan should maintain hepatitis B immunization and screening while prioritizing hepatitis C screening, diagnosis, and linkage to treatment, supported by continued surveillance among mobile and key populations as the province’s free trade port development accelerates population mobility.

Subject of Research: Infectious Disease Epidemiology

Article Title: Trends and forecasting of reported hepatitis B and hepatitis C incidence in Hainan Province, China, 2005–2020

Article References: Wang, J., Li, S., Fu, C., Su, Y., Fu, H., Tian, Y., & Lan, C. (2026). Trends and forecasting of reported hepatitis B and hepatitis C incidence in Hainan Province, China, 2005–2020. Frontiers in Epidemiology, 6, Article 1899759. https://doi.org/10.3389/fepid.2026.1899759

Image Credits: AI Generated

DOI: 10.3389/fepid.2026.1899759

Keywords: hepatitis B, hepatitis C, Hainan Province, time-series analysis, SARIMA forecasting, viral hepatitis surveillance, China, Trends, forecasting, reported, hepatitis, incidence