In a letter to the editor of the New England Journal of Medicine, the five scientists explain that serotypes O4:K12 and O4:KUT have been shown to be more virulent than other serotypes and cause seafood-associated gastroenteritis. First identified in the Pacific Northwest in 1988, these strains caused major US outbreaks in 1997 and 2004.
They were not isolated from other locations until 2012, when an outbreak affecting 28 people in the USA was linked to shellfish from Oyster Bay Harbour, New York. That same year a similar outbreak affecting 51 passengers on a cruise ship was reported in Galicia in northern Spain. This outbreak was associated with cooked seafood that had been cooled using ice made from untreated local seawater.
The authors of the letter state that the reason for the apparent spread of these pathogens is unclear, but suggest that storing imported live shellfish in local waters and discharge of water ballast from ships are both possible mechanisms. Higher than normal surface seawater temperatures may also play a part in increasing the prevalence of V. parahaemolyticus in new waters.
The letter can be found in full here.