Molecular epidemiology of norovirus outbreaks in Edinburgh, Scotland

Abstract number: P1857

Holmes A., Garcia L., Cameron F., Cloy K., Danial J., Cepeda J., Simmonds P., Templeton K.

Objectives: The aim of this study was to determine the genotypes responsible for norovirus (NoV) outbreaks in Edinburgh and to study the temporal occurrence of the genotypes to enable a better understanding of the epidemiology of the outbreaks.

Methods: A total of 161 samples positive for NoV genogroup II (GII) RNA by reverse transcription (RT) real-time PCR during routine diagnostic testing were investigated. Samples were obtained from a representative number of outbreaks (n = 66) of gastroenteritis that occurred between February 2008 and May 2009 in Edinburgh healthcare facilities. Nested RT-PCR, targeting a 311bp region of the major capsid gene, and sequencing was used to genotype the NoV strains.

Results: 118 of the 161 samples (73%) were successfully amplified and sequenced. A total of 20 NoV strains belonging to six different genotypes (GII.1, GII.2, GII.3, GII.4, GII.6 and GII.12) were detected. The predominant genotype was GII.4, which included 13 variants separated into three genoclusters, 2006a (n = 3), 2006b (n = 6) and GII.4/2007 (n = 4). The majority of outbreaks (65%) were caused by 2006b, and two variants of 2006b, v1 (Hu/GII-4/Kumamoto2/2006/JP) and v4 (Hu/GII.4/VIC4681/2007/AU). These variants circulated at different times; initially 2006b was the predominant strain causing outbreaks at multiple healthcare facilities, and continued to cause outbreaks throughout the study period. 2006b v1 was prevalent during April and May 2008, whilst 2006b v4 predominated from January 2009 until May 2009. Linking this data with the incidence of NoV during the study period showed large increases in NoV activity to coincide with the emergence of these 2006b variants.

Conclusion: In 2006, GII.4 2006a was the predominant genotype detected in Scotland. This study reveals 2006b variants are now the predominant circulating strains, in Edinburgh at least, with other types circulating for shorter periods or sporadically. Importantly, increases in norovirus activity coincided with the introduction of new NoV 2006b variants, highlighting the need for an active surveillance system to allow the rapid identification of new, highly transmissible strains.