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Eurosurveillance, Volume 11, Issue 27, 06 July 2006
Articles

Citation style for this article: Koopmans M, Harris J, Verhoef L, Depoortere E, Takkinen J, Coulombier D, International outbreak investigation team. European investigation into recent norovirus outbreaks on cruise ships: update. Euro Surveill. 2006;11(27):pii=2997. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=2997

European investigation into recent norovirus outbreaks on cruise ships: update

M Koopmans1,2 (Marion.Koopmans@rivm.nl), J Harris2,3 L Verhoef1,2, E Depoortere4, J Takkinen4, D Coulombier4, on behalf of the international outbreak investigation team

1National Institute of Public Health (RIVM), Bilthoven,The Netherlands
2DIVINE-NET
3Health Protection Agency Centre for Infections, London, United Kingdom
4European Centre for Disease Prevention and Control, Stockholm, Sweden

The European investigation into norovirus infection outbreaks on cruise ships, carried out by DIVINE- NET, the European network for the prevention of emerging (food-borne) enteric viral infections (http://www.eufoodborneviruses.co.uk/DIVINEVENT/DIVIndex.asp), is continuing. By 5 July 2006, a total of 35 outbreaks of gastrointestinal infection had been reported on 13 cruise ships travelling around Europe. Norovirus (NoV) has been confirmed as the aetiological agent for outbreaks on 9 of the 13 ships. A total of 1088 cases have been reported, of which at least 642 (59%) are known to have been in passengers and 64 (6%) in crew members. The most recent suspected outbreak was reported on 5 July.

The investigation has focused on two main hypotheses:
1. the introduction of NoV on the ships from a common source (food or water supply);
2. the circulation of NoV on cruise ships as a reflection of illness in the community, possibly increased due to circulation of new variant strains.

Of the 13 ships involved, nine have reported consecutive outbreak episodes, ranging from two to five. Samples to confirm the diagnosis have not been collected consistently in consecutive outbreaks, but the data suggests persistence of NoV on ships. Alternatively, new passengers may reintroduce the virus, precipitating new outbreaks.

The virological investigation has shown that the confirmed outbreaks are caused by two new variant GGII4 NoV strains. An open access strain matching system has been established to allow harmonised sequence comparisons worldwide for commonly used genome regions (www.rivm.nl/bnwww, follow the links to ‘Foodborne viruses in Europe’ and ‘quick typing database’). Requests for strain comparison can also be sent to fbve@rivm.nl.

A survey is ongoing among DIVINE-NET members to provide background levels of outbreak reporting in the community. A retrospective cohort study and a detailed review of hygiene protocols are planned on the ship where the most recent outbreak was reported. In addition, guidelines on NoV control in different settings are being reviewed.

Conclusion
Based on the available information, and pending the completion of the analysis of data, there is no indication that a common source event introduced NoV on these ships. The most likely hypothesis is that cruise ship outbreaks reflect increased level of illness in the community.

References:
  1. Takkinen J. Recent norovirus outbreaks on river and seagoing cruise ships in Europe. Euro Surveill 2006;11(6):E060615.2. Available from: http://www.eurosurveillance.org/ew/2006/060615.asp#2

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