This report describes an outbreak investigation starting with two closely related suspected food-borne clusters of Dutch hepatitis A cases, nine primary cases in total, with an unknown source in the Netherlands. The hepatitis A virus (HAV) genotype IA sequences of both clusters were highly similar (459/460 nt) and were not reported earlier. Food questionnaires and a case–control study revealed an association with consumption of mussels. Analysis of mussel supply chains identified the most likely production area. International enquiries led to identification of a cluster of patients near this production area with identical HAV sequences with onsets predating the first Dutch cluster of cases. The most likely source for this cluster was a case who returned from an endemic area in Central America, and a subsequent household cluster from which treated domestic sewage was discharged into the suspected mussel production area. Notably, mussels from this area were also consumed by a separate case in the United Kingdom sharing an identical strain with the second Dutch cluster. In conclusion, a small number of patients in a non-endemic area led to geographically dispersed hepatitis A outbreaks with food as vehicle. This link would have gone unnoticed without sequence analyses and international collaboration.

doi.org/10.2807/1560-7917.ES.2016.21.3.30113, hdl.handle.net/1765/91878
Eurosurveillance
Department of Virology

Boxman, I.L, Verhoef, L, Vennema, H, Ngui, S, Friesema, I.H.M, Whiteside, C, … Koopmans, M.P.G, D.V.M. (2016). International linkage of two food-borne hepatitis a clusters through traceback of mussels, The Netherlands, 2012. Eurosurveillance, 21(3). doi:10.2807/1560-7917.ES.2016.21.3.30113