[Epidemiological characteristics of leptospirosis in Sichuan province, 2004-2018]

Objective: To explore the epidemiological characteristics of leptospirosis in Sichuan province from 2004 to 2018, and provide evidence for the prevention and control of leptospirosis. Methods: The descriptive epidemiology analysis was conducted based on the epidemic data of leptospirosis collected from the national notifiable infectious disease reporting information system (NNIDRIS) and sentinel surveillance system in 11 areas in Sichuan from 2004 to 2018. The ArcGIS 10.2 software was used for mapping. The SaTScan 9.1.1 software was used to analyze spatiotemporal scanning and characteristics of temporal-spatial clusters of leptospirosis. Results: A total of 2 834 cases of leptospirosis, including 41 deaths, were reported in Sichuan from 2004 to 2018, and the reported morbidity rate was 0.23/100 000 and the mortality rate was 0.003/100 000. It revealed that leptospirosis had an overall downward fluctuated trend. The incidence of leptospirosis had obvious seasonality, mainly from the last ten-day of August to the end of September, 1-2 weeks later after rice harvesting time. The reported cases were mainly males, the male to female ratio of the cases was 2.05∶1. The incidence was higher in age group 50-65 years. The majority of reported cases were farmers, accounting for 82.75% (2 345/2 834), followed by students, accounting for 12.74% (361/2 834). However, rare cases in students had been reported since 2011. In recent years, the high-incidence areas were alternating between Mabian, Muchuan counties along the Yangtze River and Yilong county located in the Jialing River basin. According to the spatial-temporal descriptive analyses by SaTScan, there were two clustering areas in the province where most cases occurred (P<0.001). The average density of field rats in 11 sentinel surveillance areas was 5.44%(14 351/263 767), and the predominant field rats included Anourosorexsquamipes (69.07%), Apodemusagrarius (12.73%). Whatmore, the density of the Apodemusagrarius ranged from 4.60% to 0.19%, showing downward trend with the lowest level in 2018. The annual culture rate of Leptospira from rat kidney samples declined. During 2007-2018, the average positive rate of Leptospira antibodies in healthy people was 24.52%(3 271/13 339), and the predominant serogroup was Icterohaemorrhagiae. There was no replacement of Leptospira serogroup in recent years. Conclusions: The incidence of leptospirosis in Sichuan was extremely low during 2004-2018, and the incidence peak of leptospirosis occurred in rice harvesting period. The cases were mainly old farmers, and the high-risk areas were constantly alternating between the Yangtzi River and the Jialing River basin. Both the density and the carriage rate of Leptospira of Apodemusagrarius were low, and the predominant serogroup was Icterohaemorrhagiae. The average positive rate of leptospira antibodies in healthy people was very low.