title: The impact of calicivirus mixed infection in an oyster-associated outbreak during a food festival.
abstract: BACKGROUND
  Despite calicivirus food-borne outbreaks posing major public health concern worldwide, little information is at present available about the impact of caliciviruses mixed infection in an oyster-associated outbreak in China.
  
  
  OBJECTIVE
  To investigate the clinical and epidemiologic characteristics of an oyster-associated calicivirus outbreak initiated by a food festival in Shanghai, China, in April 2014.
  
  
  METHODS
  Molecular epidemiological studies based on nucleotide sequencing and phylogenetic analysis of calicivirus strains from patients.
  
  
  RESULTS
  A total of 65 of the 78 (83%) cases from this outbreak were associated with raw oyster consumption. Forty-six calicivirus strains were identified from 25 stool specimens with norovirus (NoV) GII.4 Sydney_2012, GII.13, GI.2, GI.5 and sapovirus (SaV) GI.2 being predominant genotypes and with a prevalence of triple-, double- and single-infection being 20%, 48% and 28%, respectively. Meanwhile, 13 putative NoV recombinants were indicated by the phylogenetic inconsistency between capsid and polymerase genotype, mainly including GII.Pe/GII.4 Sydney_2012. Molecular epidemiological investigation showed possible multiple route transmission in the field. The clinical and epidemiologic characteristics of the mixed point-source calicivirus outbreak also conformed to Kaplan's criteria.
  
  
  CONCLUSIONS
  This is the first reported oyster-associated calicivirus outbreak with a high prevalence of mixed infection during a food festival described in China. Our investigation underscores the importance of early surveillance and comprehensive etiologic identification of mixed point-source outbreaks and the need for reliable standards of monitoring oysters to prevent and control calicivirus food-borne outbreaks in China.
authors.affiliation: Department of Internal Medicine, Jinshan Hospital, Fudan University, No. 1508 Longhang Road, Shanghai 201508, China. Electronic address: wangyan_hf@126.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Internal Medicine, Jinshan Hospital, Fudan University, No. 1508 Longhang Road, Shanghai 201508, China. Electronic address: zhangja@mail.xjtu.edu.cn.
authors.forename: Jinan
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Institute of Antibiotics, Division of Infectious Diseases, Huashan Hospital, Fudan University, No. 12 Wulumuqi Road, Shanghai 200040, China. Electronic address: 11211300003@fudan.edu.cn.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Shen
mesh_terms: D000328:Adult; D000818:Animals; D002139:Caliciviridae / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D017250:Caliciviridae Infections / Q000453:epidemiology* / Q000821:virology; D002681:China / Q000453:epidemiology; D060085:Coinfection / Q000453:epidemiology; D004196:Disease Outbreaks; D005260:Female; D005516:Food Microbiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010125:Ostreidae / Q000821:virology*; D010802:Phylogeny; D012367:RNA, Viral / Q000032:analysis; D017423:Sequence Analysis, RNA; D055815:Young Adult
chemical_list: D012367:RNA, Viral
keywords: Mixed infection; Molecular epidemiology; Norovirus; Oyster-associated outbreak; Phylogenetic analysis; Sapovirus