Abstract:

Objective To analyze the epidemiological characteristics of scrub typhus in Xiamen City in recent years and predict the epidemic trend, so as to provide a foundation for scientific development of local preventive and control measures. Methods Data on reported cases of scrub typhus were collected in Xiamen City from 2013 to 2022, and descriptive epidemiological method was used to analyze the characteristics of time, spatial and regional distribution of the infection. In addition, the seasonal autoregressive integrated moving average (SARIMA) model was used to estimate the incidence trend in 2023-2025. Results From 2013 to 2022, a total of 862 cases of scrub typhus were reported in Xiamen. The average annual incidence rate was 2.06/100 000, with fluctuating downward trend in incidence rates in different years in general (χ²_trend=170.74, P<0.05). The temporal distribution had a more pronounced seasonality and periodicity, showing a bimodal distribution. The onset of the disease was mainly observed in May-October (737 cases, 85.50%), with 2 peaks occurring in June-July and September-October. Among the different regions, the higher average annual incidence rates were reported in Haicang District (3.56/100 000), Siming District (2.64/100 000) and Tong'an District (1.95/100 000). The male-to-female ratio of reported cases in the population distribution was 1.09∶1, and the reported incidence rate for both sexes was 2.06/100 000. The average age of reported cases was (46.97±17.35) years old, and the age of onset was primarily seen in the age group of 40-69 years old (547 cases, 63.46%). The highest number of reported cases was seen in the age group of 50-59 years old (228 cases, 26.45%), and the prevalence was the highest in population aged 60-69 years old (6.75/100 000). Of the different occupations, the highest number of reported cases was found in population of housework and the unemployed (208 cases, 24.13%), followed by farmers (197 cases, 22.85%). The median time interval between onset and diagnosis of the reported cases was 7(4, 12) d. The SARIMA(2,0,0)(0,1,1) [12] model could better predict the prevalence trend of scrub typhus in Xiamen City (RMSE=0.50, R²=0.75), and the predicted values for the number of cases in 2023, 2024 and 2025 were 42, 39 and 36 cases, respectively. The predicted data from January to September 2023 were validated, and the actual incidence data were all located in the prediction interval of the SARIMA model (RMSE=7.84, R²=0.76). Conclusion The incidence of scrub typhus in Xiamen is generally fluctuating and decreasing, and is expected to remain at a moderate epidemic level from 2023 to 2025.

Key words: Scrub typhus, Epidemiological characteristics, Trend prediction, Xiamen City