Another possible food-borne outbreak of hepatitis A in the Netherlands indicated by two closely related molecular sequences, July to October 2011.

In November 2011, a cluster of initially five cases of hepatitis A infection with closely related strains was identified in the Netherlands. England reported possibly related cases. Strains with identical sequences had been involved in previous outbreaks linked to semi-dried tomatoes. Investigation of the Dutch cluster suggested a link with ready-to-eat salads including those containing semi-dried tomatoes. Despite trace-back, a source was not identified. Vigilance is needed, and rapid sharing of data may help source-tracing. In November 2011, a cluster of five cases of hepatitis A was identified through voluntary molecular surveillance in the Netherlands. It involved two highly similar strains of hepatitis A virus (HAV) genotype IB that were closely related to strains found in travellers from a specific region in the Middle East. Both strains were identical to strains found in earlier outbreaks in the Netherlands during the first half of 2010 [1,2]. One of the sequences was closely related to one found during an outbreak in Australia in 2009 [3] and the other sequence to one that caused an outbreak in France in 2010 [4,5]. These earlier outbreaks had all been epidemiologically linked to the consumption of semi-dried tomatoes. The Dutch cluster coincided with an urgent request from England in the European reporting system EPIS, concerning the same molecular sequence [6]. The overall number of the reported hepatitis A cases was not higher than expected for that time of year. However, since the cases were not epidemiologically linked, and molecular sequencing found that the strains were rare and identical to previous outbreaks, an outbreak investigation was initiated. Close collaboration was established with the Dutch Food Safety Authority (NVWA) and the Health Protection Agency in England through telephone conferences to share updates and data [6]. With this article, we aim to alert other countries to be aware that this hepatitis strain and the contaminated product may be circulating, and to initiate source tracing if they detect the strain.