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Journal of Clinical Microbiology, August 2009, p. 2411-2418, Vol. 47, No. 8
0095-1137/09/$08.00+0     doi:10.1128/JCM.02168-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Genetic Diversity among Food-Borne and Waterborne Norovirus Strains Causing Outbreaks in Sweden{triangledown}

Maria Lysén,1 Margareta Thorhagen,2 Maria Brytting,1 Marika Hjertqvist,3 Yvonne Andersson,3 and Kjell-Olof Hedlund2*

Department of Virology,1 Centre for Microbiological Preparedness,2 Department of Epidemiology, Swedish Institute for Infectious Disease Control, Solna SE-171 82, Sweden3

Received 12 November 2008/ Returned for modification 13 February 2009/ Accepted 28 May 2009

A total of 101 food-borne and waterborne outbreaks that were caused by norovirus and that resulted in more than 4,100 cases of illness were reported to the Swedish Institute for Infectious Disease Control from January 2002 to December 2006. Sequence and epidemiological data for isolates from 73 outbreaks were analyzed. In contrast to health care-related outbreaks, no clear seasonality could be observed. Sequence analysis showed a high degree of genetic variation among the noroviruses detected. Genogroup II (GII) viruses were detected in 70% of the outbreaks, and of those strains, strains of GII.4 were the most prevalent and were detected in 25% of all outbreaks. The GII.4 variants detected in global outbreaks in health care settings during 2002, 2004, and 2006 were also found in the food-borne outbreaks. GI strains totally dominated as the cause of water-related (drinking and recreational water) outbreaks and were found in 12 of 13 outbreaks. In 14 outbreaks, there were discrepancies among the polymerase and capsid genotype results. In four outbreaks, the polymerase of the recombinant GII.b virus occurred together with the GII.1 or GII.3 capsids, while the GII.7 polymerase occurred together with the GII.6 and GII.7 capsids. Mixed infections were observed in six outbreaks; four of these were due to contaminated water, and two were due to imported frozen berries. Contaminated food and water serve as important reservoirs for noroviruses. The high degree of genetic diversity found among norovirus strains causing food-borne and waterborne infections stresses the importance of the use of broad reaction detection methods when such outbreaks are investigated.

* Corresponding author. Mailing address: Centre for Microbiological Preparedness, Swedish Institute for Infectious Disease Control, Solna SE-171 82, Sweden. Phone: 46-8-4572617. Fax: 46-8-307957. E-mail: kjell-olof.hedlund{at}smi.se

{triangledown} Published ahead of print on 3 June 2009.

Journal of Clinical Microbiology, August 2009, p. 2411-2418, Vol. 47, No. 8
0095-1137/09/$08.00+0     doi:10.1128/JCM.02168-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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