Epidemiological investigation of a foodborne outbreak in Spain associated with U.S. West Coast genotypes of Vibrio parahaemolyticus

Abstract

We describe an outbreak of seafood-associated Vibrio parahaemolyticus in Galicia, Spain in on 18th of August 2012 affecting 100 of the 114 passengers travelling on a food banquet cruise boat. Epidemiological information from 65 people was available from follow-on interviews, of which 51 cases showed symptoms of illness. The food items identified through the questionnaires as the most probable source of the infections was shrimp. This product was unique in showing a statistically significant and the highest OR with a value of 7.59 (1.52-37.71). All the nine strains isolated from stool samples were identified as V. parahaemolyticus, seven were positive for both virulence markers tdh and trh, a single strain was positive for trh only and the remaining strain tested negative for both trh and tdh. This is the largest foodborne Vibrio outbreak reported in Europe linked to domestically processed seafood. Moreover, this is the first instance of strains possessing both tdh+ and trh+ being implicated in an outbreak in Europe and that a combination of strains represent several pathogenicity groups and belonging to different genetic variants were isolated from a single outbreak. Clinical isolates were associated with a novel genetic variant of V. parahaemolyticus never detected before in Europe. Further analyses demonstrated that the outbreak isolates showed indistinguishable genetic profiles with hyper-virulent strains from the Pacific Northwest, USA, suggesting a recent transcontinental spread of these strains.

Keywords: PNW clone; ST 36; Seafood; Vibrio parahaemolyticus; tdh; trh.

Fig. 1

PFGE analysis of the outbreak strains. a PFGE profiles of all available clinical strains of V. parahaemolycus detected in Spain since 1998, including one reference strains from clinical sources isolated in the UK, and PFGE profile of outbreak strains. b PFGE of V. parahaemolyticus strains from New York outbreak (June 2012) and Pontevedra, NW Spain, August 2012 (PFGE data from New York strain courtesy Gladys Gonzalez-Aviles, CDC, USA)

Fig. 2

Genotyping analysis of the two genetic variants isolated from the outbreak. Minimum Spanning Tree based on MLST alleles constructed using categorical coefficient with the tdh+/trh+ outbreak strain includes into the ST 36 group with strains characteristic of the Pacific Northwest of North America and the second outbreak strain tdh-/trh+ with a novel ST uniquely associated with ST 417 strains, other genetic variant endemic for the Pacific NW of North America; each circle represent a different ST, the size of the circle reflects the number of isolates, numbers in branches indicate the number of loci with different alleles and orange areas designate clonal complex by Bionumerics grouping genotypes differing in a maximum of two loci

Fig. 3

Surface seawater temperatures in North West Spain, August 2012. Note significant warming trend in Pontevedra area corresponding temporally and spatially with incident of outbreak report on 18th August 2012