The impact of calicivirus mixed infection in an oyster-associated outbreak during a food festival

Abstract

BackgroundDespite 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. ObjectivesTo investigate the clinical and epidemiologic characteristics of an oyster-associated calicivirus outbreak initiated by a food festival in Shanghai, China, in April 2014. Study designMolecular epidemiological studies based on nucleotide sequencing and phylogenetic analysis of calicivirus strains from patients. ResultsA 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. ConclusionsThis 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.