Eurosurveillance - View Article

A Kroneman¹ (annelies.kroneman@rivm.nl), H Vennema¹, J Harris², G Reuter³, C-H von Bonsdorff⁴, K-O Hedlund⁵, K Vainio⁶, V Jackson⁷, P Pothier⁸, J Koch⁹, E Schreier⁹, B Böttiger¹⁰, M Koopmans¹ on behalf of the “Food-borne viruses in Europe” network

¹National Institute for Public Health and the Environment, Bilthoven, the Netherlands
²Health Protection Agency, Centre for Infections, London, United Kingdom
³Regional Laboratory of Virology, National Reference Laboratory of Gastroenteric Viruses, Pécs, Hungary
⁴Helsinki University Central Hospital, Virology Division, Helsinki, Finland
⁵Swedish Institute for Infectious Disease Control, Department of Virology, Karolinska Institute, Stockholm, Sweden
⁶Norwegian Institute of Public Health, Division of Infectious Disease Control, Oslo, Norway
⁷Health Protection Surveillance Centre, Dublin, Ireland
⁸University of Dijon, Laboratoire de Virologie, Dijon, France
⁹Robert Koch Institute, Berlin, Germany
¹⁰Department of Virology, Statens Serum Institut, Copenhagen, Denmark

A large increase in norovirus outbreaks in Hungary and Germany was reported to European national health authorities via the Foodborne Viruses in Europe network (FBVE, http://www.eufoodborneviruses.co.uk/DIVINEVENT/DIVIndex.asp) on 24 November and 4 December respectively. Subsequently, an email was sent to all FBVE members requesting a current overview on norovirus outbreaks in their country, and asking for preliminary reports on genotyping.

Thirteen country authorities participate in the FBVE network. Nine of the 11 country authorities which replied to the survey indicated an increase in norovirus activity (outbreaks and/or case reports) in October and/or November 2006 compared with the same period in 2004 and 2005 (Table). In two countries (France and Spain), no increase in norovirus activity was found. Unusually high norovirus activity already in summer 2006 was reported by the Hungarian authorities (thought to be due to a drinking-water related outbreak) as well as the Netherlands, Denmark, Ireland, Finland and Norway.

Table. Reports of norovirus cases and outbreaks across Europe, as provided by an email survey (left) and as reported to the FBVE database (right). Numbers of reports in the email survey were partly estimates, number of reports in the FBVE database are counts.

Country	data via email network						in FBVE databases
	Increasing NoV activity in October and or November or week 40-48?	Numbers of outbreaks/ cases in Oct and Nov reported after email request for data			Basis of information		Outbreaks in Oct and Nov in FBVE database			Most recent genetic information in Bionumerics database	Genotypes/variants found in Oct and Nov
		2006	2005	2004	lab database national	surveill. database national	2006	2005	2004	Most recent genetic information in Bionumerics database	Genotypes/variants found in Oct and Nov
Germany	Yes	604 outbreaks	184 outbreaks	514 outbreaks	No	Yes	134	139	0	Nov 2006	4 G II.4 of which one variant 2006 b and 3 variant 2006a, and 4 other genotypes
Denmark	Yes	249 lab samples	38 lab samples	222 lab samples	Yes	No	0	2	2	Sep 2006	2 II.4, both variant 2006a¹
Spain²	No	2 outbreaks	6 outbreaks	12 outbreaks			1	3	4	Oct 2006	1 II.4, variant 2006a
Finland	Yes	~ 120 cases	~ 10 cases	~ 10 cases	Yes	No	0	2	0	Sep 2006
France	No	3 outbreaks	1 outbreak	2 outbreaks	Yes	No	7	1	2	Oct 2006	2 II.4, variant 2006a , 1 other genotype
England and Wales³	Yes	768 outbreaks and round 756 lab samples	83 outbreaks and 281 lab samples	374 outbreaks and 682 lab samples	Yes	Yes	11	54	69	May 2006	43 G II.4 of which 20 2006a, 11 2006b and 12 non a or b 15 non G II.4^1*
Hungary	Yes	81 outbreaks	17 outbreaks	24 outbreaks	Yes		21	3	14	Nov 2006	7 G II.4 of which 5 variant 2006b and 2 2006a
Ireland	Yes	7 outbreaks	0 outbreaks	22 outbreaks	No	Yes	11	5	40	Oct 2006	1 G II.4 variant 2006a, 1 other genotype
Italy	unknown						1	0	2	Aug 2006
The Netherlands	Yes	36 outbreaks	5 outbreaks	68 outbreaks	Yes		36	3	54	Nov 2006	26 G II.4 of which 19 2006a and 7 2006b
Norway	Yes	~ 160 cases	~ 65 cases	~ 35 cases	Yes	No	1	7	0	none
Sweden	Yes	~ 400 cases	~ 50 cases	~ 350 cases	Yes	No	1	2	0	Oct 2006	1 G II.4, variant 2006a
Slovenia	Yes	7 outbreaks	6 outbreaks	5 outbreaks	Yes	No	0	5	1	Sep 2006

¹Data of number of samples and genotypes not yet in the FBVE sequence database, but sent by email
²Data from Valencia and Catalonia
³Outbreaks reported from virus reference laboratory only. Laboratory data are from England and Wales, these data will include outbreaks and sporadic cases. The routine laboratory data cannot be linked to the data from the reference lab

The norovirus isolates causing 108 outbreaks which started in October and November 2006 have been characterised, and 87 (81%) belonged to genotype G.II 4, which has been the predominant genotype in recent years. Twenty-one (19%) belonged to other genotypes. Of the 87 G II.4 isolates characterised, 51 (47%) were G II.4 new variant 2006a and 24 (22%) were variant 2006b¹. Twelve G II.4 isolates (11%) could not be assigned to a variant.

All norovirus outbreak isolates which were reported to FBVE sequence database in the seasons 2004/2005, 2005/2006 and the present season so far are shown (Figure). The first new variants of genotype GII.4 2006 appeared during the 2005/2006 season, and became the predominant strain in summer 2006. For variant 2006a, the first entry in the database is from an outbreak or case in England in 2005. The first 2006b variant was reported from Spain in December 2005 after an outbreak in a residential institution. In the spring of 2006, this variant was found to be circulating widely, causing at least 45 outbreaks of norovirus illness on cruise ships sailing across Europe. It is believed that the emergence of the variants 2006a and 2006b and the increase in outbreaks on cruise ships might well be the forewarning of a very active norovirus season. This prediction is based on observations in 1996, 2002 and 2004, when the appearance of new variants within genotype GII.4 coincided with high levels of outbreak reporting worldwide [1,2,4].

Figure. Genotypes/variants in seasons 2004/5, 2005/6 and the start of 2006/7
Using all genetic information in the Bionumerics database:
- from outbreaks and from sequences submitted without background data (this last group is small)
- from sequences of part of the polymerase gene (ORF 1) and 2 different non overlapping regions of the capsid gene (ORF2).

2006/2007 norovirus season likely to see high activity

The different country reports indicate that the norovirus season has already started in most areas. As predicted, 2006/2007 is likely to be a highly active norovirus season, with the new variants of genotype G II.4 2006 being predominant [3]. It is therefore recommended that hospitals and nursing homes inform their staff about the possibility of norovirus outbreaks and provide information on the clinical presentation. They should also consult their outbreak protocols, adopt them if necessary and strengthen preventive measures, in order to be prepared for the present outbreak season.

The data provided in response to this email survey come from local datasets, and are not (yet) visible in the FBVE database. The FBVE network maintains a web-based database to which 13 national authorities report norovirus outbreaks, along with epidemiological and laboratory data. The average delay between the onset of an outbreak and the reporting of this outbreak to the FBVE database is quite long. For the outbreaks reported in the quarterly period of July to September 2006, the average delay was 111 days, ranging from 23 days (Sweden) to 436 days (Italy). As a result, in its present form, the FBVE database can not be used to compare reports from Germany and Hungary with the rest of the European situation. Since typing norovirus strains takes some time, there is limited information on the circulating noroviruses at the moment. A complete comparison will be possible towards the end of this winter.

*Correction 15 December. The original text incorrectly stated '15 non G II.42'

Footnote. Comparisons of genome sequences to determine if norovirus outbreak strains elsewhere belong to the same new variant lineage can be done via an open access strain matching system (http://www.rivm.nl/bnwww). This was established by the FBVE network to allow harmonized sequence comparisons worldwide for commonly used genome regions (follow the links to ‘Food-borne viruses in Europe’ and ‘quick typing database’. Requests for strain comparison can also be sent to fbve@rivm.nl).