Trends and forecasting of reported hepatitis B and hepatitis C incidence in Hainan Province, China, 2005-2020.

Objective: To assess long-term trends, seasonality, forecasts, and ecological associations with tourist visits for reported hepatitis B virus (HBV) and hepatitis C virus (HCV) incidence in Hainan Province from 2005 to 2020. Methods: Reported HBV and HCV incidence data from Hainan, national Global Burden of Disease (GBD) estimates for China, and annual tourist visit data were analyzed. Joinpoint regression assessed temporal trends, seasonal-trend decomposition using loess evaluated monthly variation, and seasonal autoregressive integrated moving average models generated forecasts. Spearman rank correlation analysis examined tourism associations, with sensitivity analyses excluding 2020 and using first-differenced and linearly detrended series. Results: Reported HBV incidence declined from 2005 to 2008, increased from 2008 to 2018, and then showed a non-significant decline through 2020; the overall average annual percent change (AAPC) was +3.37%. Reported HCV incidence increased until 2015 and subsequently declined, with an overall AAPC of +14.54%. National GBD estimates showed overall AAPCs of -0.54% for HBV and -1.52% for HCV. No significant differences among calendar months were detected. Under continuation of historical reporting patterns, the annualized projected reported HBV incidence in 2030 was 12.00 per 100,000 population (95% prediction interval: approximately 0.00-121.20), numerically close to the study-defined reference value of 12.20. The corresponding HCV estimate was 22.54 per 100,000 population (approximately 0.00-39.10), approximately 6.4 times the study-defined reference value of 3.55. The wide prediction intervals indicated substantial long-term forecast uncertainty. In 2020, observed mean monthly reported HBV and HCV incidence rates were 27.3% and 9.5% lower than forecasted values, respectively. In raw annual analyses, tourist visits correlated with reported HBV and HCV incidence Conclusion: Reported HBV and HCV incidence in Hainan showed distinct phased changes without significant monthly differences. The forecasts represent projections under historical reporting patterns and should not be interpreted as evidence of progress toward WHO elimination targets. Tourism associations were exploratory and ecological and do not support causal inference. Continued surveillance and strengthened HCV screening, diagnosis, and linkage to treatment remain important.