Surveillance results for Leptospira antibody level in healthy population in Yunnan, 2014−2018

  Objective  To understand the antibody level and infected serogroup distribution of Leptospira in healthy population in the natural foci of leptospirosis in Yunnan province, analyze the local incidence trend of leptospirosis and provide scientific basis for the prevention and control of leptospirosis in Yunnan.

  Methods  The serum samples of healthy people collected from three national surveillance sites of leptospirosis in Huaping, Menglian and Mengla counties of Yunnan were used for dark field microscope agglutination test with a panel of 15 pathogenic Leptospira live antigens representing 15 different serogroups.

  Results  A total of 300 serum samples of healthy people were collected from three leptospirosis monitoring sites from 2014 to 2018 in Yunnan. The serum positive rate of Leptospira antibody in the five years were 29.67%, 28.33%, 15.67%, 10.33% and 14.33% respectively, and the overall serum positive rate of Leptospira antibody was 19.67%. The difference in serum positive rate of Leptospira antibody among the five years were significant (χ²=58.232, P<0.05). The positive rates in Huaping, Menglian and Mengla counties were 15.40%, 19.60% and 24.00% respectively. The serum positive rate of Leptospira antibody in Mengla was higher than the overall serum positive rate of the five years, and the positive rates in Huaping and Menglian were lower than the overall serum positive rate of the five years. The differences in the serum positive rate of Leptospira antibody among the three areas were significant (χ²=11.705, P<0.05). There were no significant differences in the serum positive rate of Leptospira antibody among the different age groups (χ²=7.131, P>0.05). Among the 295 positive serum samples detected, 15 serogroups of Leptospira were detected, in which the Icterohaemorrhagiae was predominant serogroup, accounting for 35.05%, followed by Pyrogenes and Australis, accounting for 14.69% and 12.37% respectively.

  Conclusion   The serum positive rate of Leptospira antibody in healthy population in three national surveillance sites in Yunnan showed a downward trend from 2014 to 2017, but slightly increased in 2018. The species and types of Leptospira infecting people were complex, and 15 serogroups were detected, with Icterohaemorrhagiae as the main serogroup.