Epidemic foci of hemorrhagic fever with renal syndrome in Shandong Province, China, based on patients, rodents and molecular epidemiology characteristics, 2012-2015

Background Hemorrhagic fever with renal syndrome (HFRS), an infectious disease caused by hantaviruses, is endemic in China and remains a serious public health problem. Historically, Shandong Province has had the largest HFRS burden in China. However, we do not have a comprehensive and clear understanding of the current epidemic foci of HFRS in Shandong Province. Methodology/Principal Findings The incidence and mortality rates were calculated, and a phylogenetic analysis was performed after laboratory testing of the virus in rodents. Spatial epidemiology analysis was applied to investigate the epidemic foci, including their sources. A total of 6,206 HFRS cases and 59 related deaths were reported in Shandong Province. The virus carriage rates of the rodents Rattus norvegicus, Apodemus agrarius and Mus musculus were 10.24%, 6.31% and 0.27%, respectively. The phylogenetic analysis indicated that two novel viruses isolated from R. norvegicus in Anqiu City and Qingzhou City were dissimilar to the other isolated strains, but closely related to strains previously isolated in northeastern China. Three epidemic foci were defined, two of which were derived from the Jining and Linyi epidemic foci, respectively, while the other was the residue of the Jining epidemic focus. Conclusions/Significance The southeastern and central Shandong Province are current key HFRS epidemic foci dominated by A. agrarius and R. norvegicus, respectively. Our study could help local departments to strengthen prevention and control measures in key areas to reduce the hazards of HFRS. Author summary Hemorrhagic fever with renal syndrome (HFRS) is a global infectious disease, which is still a serious public health threat in China today. The reported HFRS cases in Shandong Province accounted for approximate one third of total cases in the whole country. HFRS is a zoonosis mainly caused by Hantaan virus (HTNV) and Seoul virus (SEOV), which natural rodent hosts are A. agrarius and R. norvegicus, respectively. To explore the current HFRS epidemic foci based on patients, rodents and molecular epidemiology characteristics in Shandong Province, we collected the records of HFRS cases from whole province and the rodents captured in 14 surveillance sites. We found that the epidemic situation of HFRS is quiet different in temporal and spatial distribution. Three epidemic foci were defined based on patients, rodents and molecular epidemiology characteristics. The situation of HFRS epidemic foci in Shandong Province was clear. Our study provides a reference for relevant departments to develop key prevention strategies.

The study area is located in the North China Plain, in eastern China (34°22'to 100 38°23'north latitude, 114°19' to 122°43' east longitude, Fig 1), with a population of 5 101 more than 99 million and an area of 158,000 km 2 . Shandong Province has a large 102 population of agricultural workers and high land cultivation rate in China. The central 103 region is mountainous and hilly, which is surrounded by plains.

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The records of HFRS cases between 2012 to 2015 were obtained from the China to Jan) based on the two annual HFRS incidence peaks.

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The PCR was performed to amplify a partial L sequence, using primer pairs as 130 previously described [9]. Amplification result was sequenced and compared with data

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From 2012 to 2015, 6,206 HFRS cases and 59 related deaths were reported in 155 Shandong Province, and the annual incidence rate, mortality rate and case fatality rate 156 ranged from 1.15 to 1.87 per 100,000, 0.01 to 0.02 per 100,000, and 0.80% to 1.07%, 157 respectively (Table 1). During the study period, the annual HFRS incidence rate in 158 Shandong Province peaked in 2013, then decreased year by year, and reached its 159 lowest point in 2015. In addition, there were two incidence peaks each year, the small 160 peak was from April to June and the larger one was from October to January.

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However, mortality rates and case fatality rates declined year by year. The deaths 162 mainly occurred from September to January (Fig 2). As for spatial distribution,

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The plus sign represented the location of deaths.   branch. In addition, the genetic diversity associated with the SEOV branches indicated 235 that they were more homogeneous than the HTNV branches, which had a higher 236 degree of genetic diversity.   Province, indicating the epidemic foci during the study period.

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The epidemic foci comprised two major foci, designated Regions a and b, which is 263 located in southeastern and central Shandong Province, respectively, and a smaller 264 one designated Region c in southwestern Shandong Province (S2 Table). Among the characteristics of the disease, virus host and laboratory testing were analyzed in 295 this study, and the current epidemic foci were identified.

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Overall, the annual HFRS incidence rate exhibited small fluctuations during the 297 study period, peaking in 2013, then decreasing year by year, and reaching its lowest 298 point in 2015. There were still annual incidence peaks, which comprised a small peak 299 in late spring to early summer and a big peak in autumn to winter. The small peak is 300 associated with indoor-related infections linked to R. norvegicus breeding activity, 301 while the big peak is mainly due to the increased contact between people and wild rats 302 when they work in fields, and the migration of wild rats from fields to residential 303 areas for foraging in the later period [14].

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It is worth noting that 88% of all deaths occurred in September to January. Previous  Although the HV carriage rates among rodents in Regions b and c were higher than 358 that associated with Region a, the severity of the epidemic situation was less severe,

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suggesting that the HV-susceptible population appears to be more susceptible to the 360 HV strains in Region a (which mainly belong to the HTNV genotype). Interestingly, populations are also important factors [15,[25][26][27][28][29]. Therefore, we believe that a further 369 study should be performed to explore the factors underlying our result.