Acute gastroenteritis outbreak caused by a GII.6 norovirus

Abstract

Aim: To report an acute gastroenteritis outbreak caused by a genogroup 2 genotype 6 (GII.6) strain norovirus in Shanghai, China.

Methods: Noroviruses are responsible for approximately half of all reported gastroenteritis outbreaks in many countries. Genogroup 2 genotype 4 strains are the most prevalent. Rare outbreaks caused by GII.6 strains have been reported. An acute gastroenteritis outbreak occurred in an elementary school in Shanghai in December of 2013. Field and molecular epidemiologic investigations were conducted.

Results: The outbreak was limited to one class in an elementary school located in southwest Shanghai. The age of the students ranged from 9 to 10 years. The first case emerged on December 10, 2013, and the last case emerged on December 14, 2013. The cases peaked on December 11, 2013, with 21 new cases. Of 45 students in the class, 32 were affected. The main symptom was gastroenteritis, and 15.6% (5/32) of the cases exhibited a fever. A field epidemiologic investigation showed the pathogen may have been transmitted to the elementary school from employees in a delicatessen via the first case student, who had eaten food from the delicatessen one day before the gastroenteritis episodes began. A molecular epidemiologic investigation identified the cause of the gastroenteritis as norovirus strain GII.6; the viral sequence of the student cases showed 100% homology with that of the shop employees. Genetic relatedness analyses showed that the new viral strain is closely related to previously reported GII.6 sequences, especially to a strain reported in Japan.

Conclusion: This is the first report to show that norovirus strain GII.6 can cause a gastroenteritis outbreak. Thus, the prevalence of GII.6 noroviruses requires attention.

Keywords: Gastroenteritis; Genetic relatedness analyses; Genogroup 2 genotype 6 genogroup; Noroviruses; Outbreak.

Figure 1

Diagram of the genetic structure of the virus. The RNA genome is organized into three open reading frames (ORF1, ORF2, and ORF3) that encode the designated nonstructural and structural proteins. The nonstructural protein consists of p48, nucleoside triphosphatase (NTP), p22, viral genome-linked protein (VPg), 3C-like protease (3C), and RdRp. VP1, the major capsid protein, is further organized into N-terminal, shell (S), and protruding (P) domains defined by the indicated VP1 amino acid residues. VP2 is a minor structural protein. The diagnostic and genotyping primers used in the RT-PCR assay targeting conserved areas are shown in red (A-D).

Figure 2

Genetic relatedness among reported genogroup 6 genotype 6 norovirus strains. The consensus sequence was input into the BLAST, and a distance tree of “100 Blast Hits on the Query Sequence” was drawn using the “Fast Minimum Evolution” method. The accession numbers from the NCBI for all strains are presented. The genetic distance bar is shown in the lower left of the figure.