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Published Date: 2012-02-11 09:32:10
Subject: PRO/EDR> Hepatitis A - The Netherlands: possible food-borne outbreak
Archive Number: 20120211.1039190

HEPATITIS A - THE NETHERLANDS: POSSIBLE FOOD-BORNE OUTBREAK
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Date: Thu 9 Feb 2012
Source: Eurosurveillance, Volume 17, Issue 6 [abbreviated & edited]
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20079

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

Authors: Fournet N, Baas D, van Pelt W, Swaan C, Ober HJ, Isken L, Cremer J, Friesema I, Vennema H, Boxman I, Koopmans M, Verhoef L.

In November 2011, a cluster of 5 cases of hepatitis A was identified through voluntary molecular surveillance in the Netherlands. It involved 2 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 1st 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 [Epidemic Intelligence System], 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.

HAV surveillance in the Netherlands
HAV infections are notifiable in the Netherlands and reported to the National Institute for Public Health and the Environment (RIVM) according to standardised criteria [7]. Sera from confirmed hepatitis A cases, if available, are sent to the RIVM by the laboratories. Viral RNA is extracted from IgM positive sera, and the 460 nt VP1/2A region is sequenced and compared to sequences recorded in the Dutch [8] and an international HAV sequence database of the Food-Borne Viruses in Europe (FBVE) network [9].

From July to October 2009 and July to October 2010, respectively, 66 and 111 hepatitis A cases were reported in the Dutch mandatory notification, of which 14 and 53 acquired their infection in the Netherlands. Over the same period in 2011, there were 68 overall hepatitis A cases of which 24 acquired their infection in the Netherlands.

Outbreak investigation
Confirmed cases were defined as laboratory-confirmed HAV cases who had no travel history to endemic countries, no male-to-male sexual contacts and was therefore considered as exposed to an unknown source in the Netherlands, who had a date of symptom onset from July to November 2011 and who was infected with the specific genotype IB strain identical to strains that caused previous outbreaks in Europe and Australia in 2009–10 [1-5], i.e. Hu/Netherlands/RIVM-006/2010, closely related to Genbank accession number FJ687511, or Hu/Netherlands/RIVM-077/2010, closely related to strain FR-2010-LOUR, (GenBank Acc. No. GU646039). Cases related to primary cases and with onset of illness two weeks or more after the primary case were considered secondary cases. A probable case followed the same criteria but without laboratory confirmation.

Cases were contacted by the Dutch municipal health services and were requested to complete a questionnaire. The questionnaire included personal information like date of birth, sex, place of residence, vaccination status, symptoms, date of symptom onset and food history in the period 2 to 6 weeks before symptom onset. As recommended by the NVWA, questions on food consumption included a wide range of food products imported from the Middle East because of the similarity of the outbreak strain to strains in travellers from Middle East. The NVWA performed source tracing on the basis of questionnaire information, and tested the indicated food product for presence of hepatitis A RNA using methods described elsewhere [10].

The FBVE network [11] was alerted and asked to share sequences in the international database.

[For the description of the cases and the literature references cited, interested readers should download the original text via the source URL. - Mod.CP]

Conclusion and recommendations
Seven confirmed hepatitis A cases and one probable case were identified in the Netherlands with HAV genotype IB strains identical or closely related to the ones found recently in England and Australia and in previous food-borne outbreaks in the Netherlands, Australia and France. All cases that completed the questionnaire indicated consumption of RTE [ready-to-eat] salads, including those containing semi-dried tomatoes, during their incubation period. However, only 3 cases specifically indicated to have consumed semi-dried tomatoes. Because of the low number of cases, the long and variable incubation period, the long time between dates of onset of the 1st and of the last cases, and the complexity of the traceback, no common source could be identified. These were also the reasons for not including controls in our study. This might be considered a limitation, since we were not able to find an association to a single food product.

Until the time of publication of this report, no new cases have been reported. Nevertheless, we cannot exclude contaminated food items like RTE salads or semi-dried tomatoes being in circulation. Given the difficulty of identifying and tracing an international common food-borne source, combining information on all infected cases is of utmost importance. We are therefore interested in all cases infected with the HAV IB strains described here. The HAV database of the FBVE network can be used to compare sequences. Information on linked cases and requests for access to the database or assistance in source tracing activities can be addressed by email tofbve@rivm.nl.

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[Previously, strains with identical sequences had been involved in outbreaks linked to semi-dried tomatoes. Investigation of a recent Dutch cluster of hepatitis A cases suggested a link with ready-to-eat salads including those containing semi-dried tomatoes. Despite trace-back, a source was not identified. However this investigation illustrates the value of genome sequence analysis in the investigation and tracing of common food-borne sources across national borders. - Mod.CP]

[For the HealthMap/ProMED map of the Netherlands, see http://healthmap.org/r/1r1l. - Mod.MPP]

See Also