Spatiotemporal clustering of anthrax and molecular typing of Bacillus anthracis in Ningxia Hui Autonomous Region, 2019 – 2022

ObjectiveTo analyze the spatiotemporal clustering of anthrax cases in the Ningxia Hui Autonomous Region from 2019 to 2022 and to perform molecular typing of 14 strains of Bacillus anthracis (B. anthracis) isolated during the same period. MethodsData on anthrax cases reported in Ningxia Hui Autonomous Region (Ningxia) from 2019 to 2022 were collected, and spatiotemporal cluster analysis was performed using SaTScan software with districts and counties as units. A total of 14 strains of B. anthracis isolated from local anthrax cases from 2019 to 2021 were subjected to molecular typing analysis using canonical single nucleotide polymorphisms (CanSNPs), twenty-five marker multilocus variable number tandem repeat analysis (MLVA-25), and single nucleotide repeat (SNR-4) methods. ResultsA total of 80 anthrax cases, all of which were cutaneous anthrax, were reported in Ningxia during the 3-year period. SaTScan spatiotemporal cluster analysis revealed a spatiotemporal cluster in north-central Ningxia from 2021 to 2022, with a primary cluster in Yongning county [P < 0.01, relative risk (RR) = 13.83] and secondary clusters in Lingwu city and Litong district (P = 0.022, RR = 3.47). The genetic relationships of the 14 B. anthracis strains isolated during the same period were defined as: A.Br 001/002 subgroup, 6 different MLVA genotypes within A3.b gene cluster, of which 3 common genotypes were defined as 2, 3, and 5 PHANA genotypes, respectively, by SNR-4 analysis; SNR-4 analysis showed 12 SNR genotypes. ConclusionThe incidence of anthrax in Ningxia showed an increasing trend from 2019 to 2022. One of the reasons for the formation of spatiotemporal clusters of anthrax in 2021 – 2022 may be the formation and development of natural foci. Molecular typing revealed that the genetic relationship of the strains isolated in Ningxia from 2019 to 2022 was relatively homogeneous, with abundant genetic diversity within the same genetic relationship.