Epidemiological characteristics and molecular typing of Salmonella typhimurium in Shanghai

[Objective] To study the molecular epidemiological characteristics of Salmonella typhimurium(S.typhimurium) in diarrhea patients in Shanghai from 2006 to 2007. [Methods] A retrospective analysis from 2006 to 2007 was done to explore the source of food-borne S.typhimurium and make comparison in its drug resistance to antibiotics between food-borne and diarrhea strains.Data of S.typhimurium survey of patients on Global-Salm-Surv(GSS) and food were analysed,including serotype,drug resistance and pulsed field gel electrophoresis(PFGE). [Results] The number of diarrhea cases of S.typhimurium comfirmed by culture method was only next to that of S.enteritidis in cases of nontyphoidal Salmonella infection in Shanghai between 2006 to 2007.Food-borne S.typhimurium strains were mostly from poultry(64.4%) and meat products(17.8%).The antibiotic resistance of food-borne S.typhimurium was higher than those from clinical isolateed(P0.05).Seven food strains and 44 diarrheal strains were divided into 23 PFGE subtypes.The dominating subtypes were type1(8 strains),type2(6 strains),type29(4 strains),type49(8 strains) and type6(4 strains).Only in 7 cases,the diarrhea strains subtypes matched with food subtypes(4 strains were subtype 49,the other 3 strains subtype 6,15.9%,7/44.Strains of PFGE subtype 6,13.3%,6/45).Diarrhea strains PFGE subtype 1 were 2 cases and 6 cases in 2006 and 2007 respectively.Subtype 2 were 4 cases and 2 cases in 2006 and 2007 respectively. [Conclusion] Diarrhea with S.typhimurium has epidemiological characteristics of being highly sporadic and sporadic outbreak in Shanghai.The dominant clone types which do not match with strains from local food are PFGE subtype 2 and 1.The genetic homology are low between strains from contaminant local fresh animal meat and strains from diarrhea patients.We guess the origin of infection may be secondary food contamination by non-local patients.We suggest that epidemiological investigation should be enhanced to expose the latent infectious origin and transmission route.