Analysis on epidemiological characteristics of 4 species natural-focal diseases in Shandong Province, China in 2009-2017: a descriptive analysis

Background Natural-focal diseases have always been a kind of serious disease that endangers human health. It threatens about 100 million people in Shandong Province, and causes illness in thousands of people each year. However, information on the epidemiological characteristics of natural-focal diseases in Shandong Province has been limited. The purpose of the study is to describe and analyze the epidemiological characteristics of natural-focal diseases in Shandong Province, 2009-2017. Methods We describe the incidence and distribution of 4 species natural-focal diseases in Shandong Province using surveillance data from 2009-2017. Results From 2009-2017, 11123 cases of 4 species natural-focal diseases including 257 deaths were reported in Shandong Province, China. The 4 species natural-focal diseases were severe fever with thrombocytopenia syndrome (SFTS), human granulocytic anaplasmosis (HGA), typhus and scrub typhus respectively. The high-risk groups of the 4 species diseases all were farmers and the elderly. The incidence rate of scrub typhus was significantly higher in females, however, this difference was not seen in the other 3 diseases. The 4 species diseases were mainly clustered in middle-southern part of Shandong (Mount Yimeng) and Shandong Peninsula (Laoshan Mountain). The annual incidence of SFTS and scrub typhus had increased in the mass, typhus had been relatively stable, and HGA had declined. However, the popular range of SFTS had been expanding, HGA had been shrinking, and typhus and scrub typhus were unchanged. The epidemic period of SFTS and HGA was from May to October, typhus was from October to November, scrub typhus was from September to November in Shandong Province. The fatality rates of SFTS, typhus, scrub typhus, HGA were 9.19%, 0%, 0.01%, 2.24%, respectively. Conclusions Our study described and analyzed the prevalence of natural-focal diseases in Shandong, and confirmed that age was closely related to the SFTS fatality rate. This study may be applicable to an improved understanding of the prevalence of natural-focal diseases in Shandong Province in recent years and the better development of the accurate prevention and control strategies for natural-focal diseases in Shandong Province. Author Summary Natural-focal diseases are a serious public health problem in Shandong Province, China. It threatens about 100 million people in Shandong Province, and causes illness in thousands of people each year. This study used the monitoring data from Shandong Province for 2009-2017 to describe and analyze the epidemiological characteristics of the 4 species natural-focal diseases. The results showed that the risk population of natural-focal diseases in Shandong Province was farmers and the elderly, the epidemic season was mainly in summer and autumn, the middle-southern part of Shandong Province and Shandong Peninsula were more seriously affected compared with other regions. In addition, the epidemic area of SFTS was expanded, with a fatality rate of 9.19%. These findings indicated that public awareness of natural-focal diseases should be raised in the epidemic focus, especially for farmers, and further efforts should be strengthen specially in high-risk areas and during the epidemic season.

types of natural-focal diseases were reported in Chinese journals only [5]. Natural-focal diseases 70 constitute a serious threat to the public health. As a large agricultural and population province in Province in recent years. 81 In order to make the study of the epidemic situation of natural-focal diseases more representative, 82 we chose 4 species natural-focal diseases with low to high incidence levels to represent the overall 83 incidence of natural-focal diseases in Shandong Province. At the same time, these 4 species 84 natural-focal diseases also represent 3 different kinds of insect borne diseases. The incidence rate    The age distribution, gender distribution, occupation distribution, seasonal distribution and regional 125 distribution of the cases were summarized using Excel 2010, and IBM SPSS Statistics 24.0 (online) 126 was used to perform the statistical analysis. The different rates were analyzed using the χ 2 test. Trend 127 test was analyzed using the Linear-by-linear Association. All tests were 2-tailed and statistical 128 significance was set at P < 0.05. The base diagrams in Figure 1 and Figure 6 were from the Resource 129 and Environment Data Cloud Platform. The software ArcGis10.2 was used to plot the topographic 130 map of Shandong Province and the geographical distribution of cases (Fig 1 and Fig 6).

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Ethical approval 132 It was determined by the National Health and Family Planning Commission, China, that the 7 133 collection of data from natural-focal diseases cases was part of a continuing public health 134 surveillance of a notifiable infectious and was exempt from institutional review board assessment.  Table 1).   individuals aged over 40 years ( Table 1). The highest peak of age group distribution of number of 167 SFTS cases occurs in the 60-65 age group. However, the highest peak of the age group distribution 168 of SFTS incidence rate lags behind 2 age groups and appears in the 70-75 age group ( Fig 5A).       2/11) and Weifang had the lowest (0.84%, 2/239), no deaths were reported in other 6 cities (Table 3).     Fig 6).  (Table 3). cases/1,000,000) (Fig 2A).  Fig 6).  typhus cases compared to the other age groups but had a lower incidence rate than the 65-70 age 288 group which showed the highest incidence rate among the groups (Fig 5D).  (Table 3).

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The epidemic peak of typhus in Shandong was from October to November, which was different 369 from other typhus epidemic areas, such as those in Henan, Yunnan, and Zhejiang provinces[26-28].

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The reason for this may be that Shandong is located in the north of these epidemic areas, with lower people. If they are infected with these 4 species diseases, elderly may get severe diseases and go to 395 hospital for treatment [36,37]. It is thereby that more elderly cases were identified.

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The highest peaks of the age group distribution of the incidence rate of the four diseases lag 397 behind the highest peak of the age group distribution of the number of cases 1 or 2 age groups. The 398 60-65 age group had the highest number of cases (except HGA), but the 70-75 age group had the 399 highest incidence rate (except scrub typhus). That is related to the age structure of the population in 400 Shandong Province. Compared with the 60-65 age group, the 70-75 age group has a smaller 401 population base, so the incidence rate is higher. Therefore, this may also reflect that the 70-75 age 402 group is the highest risk group for natural-focal diseases in Shandong Province.

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The results showed that the incidence of scrub typhus among females was higher than that 404 observed in males, which is consistent with previous studies [17,18]. Two factors may contribute the 405 result. First, the increased proportion of females engaging in outdoor activities [38]. There are some limitations in our study. First, since the case data were obtained from a passive