Molecular Epidemiological Study On GAS Isolates Associated With AGN Outbreaks In Guizhou, 2005

Group A streptococcus(GAS) or Streptococcus pyogenes can cause a variety of human diseases,including scarlet fever,streptococcal toxic shock-like syndrome(STSS),rheumatic fever,acute glomerulonephritis (AGN),and so on.Among them,acute poststreptococcal glomerulonephritis(APSGN),the protype of AGN,being the most common nephritis affecting children,has still continued a wide distribution all over the world.In recent years,there have been some reports about the outbreaks of APSGN in China,but no information of epidemiology or genetic background on nephritogenic GAS stains is available yet.In November,2005,there was an AGN outbreak in middle and primary schools reported by Rongjiang county and Leishan county of Guizhou province.This outbreak had relatively large scope which covered 2 counties,11 townships and several primary schools.Among 62 cases reported,2 patients died and most of them were students in primary schools(92%).The AGN outbreak had induced panic in parents of children and affected the regular teaching in schools.In November 14, China CDC organized an expert team to control the outbreak and perform the investigation.AGN outbreak was supposed to be an acute poststreptococcal glomerulonephritis.To further identified the pathogen and cause of outbreak,China CDC conducted another investigation, which include 629 students in 8 primary schools.A total of 368 swabs were collected to perform the pathogenic analysis on the outbreak and identified the outbreak strain.In this study,several methods of genotyping for GAS used in most epidemiological studies,including M protein gene(emm) sequence typing, serum.opacity factor gene sequence typing,pulsed field gel electrophoresis(PFGE) analysis and multi locus sequence typing(MLST) were used.Among them,emm typing is the current 'gold standard' method for genotyping GAS.emm type analysis was firstly performed on 68 GAS strains isolated from 368 swabs,and a total of 11 different of emm types were identified.Analysis of the emm type distribution in two counties,different schools(epidemic school,sporadic school,unaffected school),different population(AGN patients and asymptomatic carriers) identified two emm types to be associated with the outbreak,as emm60.1 and emm63.0,indicating outbreaks in two counties were caused by the two distinct emm types respectively.PFGE,MLST,superantigen(Sag) gene profiles,and antibiotic resistance analysis was also conducted on the two types of outbreak strains.PFGE patterns of each emm type isolates showed identical or closely related gene background.The two emm type strains were identified as ST53 and ST426 by MLST analysis respectively and the clonal population structure was also constructed for the GAS isolates available in the MLST database.However,Sag gene profiles of two outbreak strains were analyzed by PCR amplification.A total of 7 toxic genes were amplified including 3 chromosomal genes (speB,speG,smeZ) and 4 genes located on mobile DNA(speA,speC, speH,speI).As the results shown us,emm60.1 isolates possessed only speB gene.For the 13 isolates of emm63.0,all of 3 chromosomal Sag genes were PCR positive,and 12 were positive for speA and speC genes, while 1 was positive only for speC gene.The results microbial sensitivity tests for 68 GAS isolates showed that the resistant rate of two outbreak strains to erythromycin and tetracycline were both 100%,and the one of the non-outbreak strains to the antibiotics was 63.6%and 90.9%The results showed that the outbreaks in the two counties adjacent to each other were caused by distinct GAS strains,emm60.1 and emm63.0 type respectively.It is the first time to report M63 GAS to be nephritogenic.Two types of outbreak strains had different Sag gene profiles and antibiotic resistance analysis indicated that GAS resistant to erythromycin was epidemic in the locality.High resistant rate to erythromycin of GAS should be of think highly for medical department, and GAS antibiotic survey on health population is recommended to obtain the real situation of antibiotic resistance.Correct choice of antibiotics by clinician is very important for the control of GAS epidemic in the population.