Molecular epidemiological characteristics of norovirus outbreaks in Qingdao, 2014-2016
Objective 
To analyze the molecular epidemiological characteristics of norovirus (NoV) outbreaks in Qingdao between 2014 and 2016. 
 
 
Methods 
Stool samples were collected from NoV outbreaks between January 2014 and December 2016 and detected by real-time RT-PCR. NoV open reading frame 1 (ORF1) and ORF2 were partially amplified by RT-PCR. The amplified products were further analyzed by gene sequencing and genotyping. Phylogenetic analysis was conducted by using MEGA 6.0 software package. 
 
 
Results 
A total of 23 NoV outbreaks, involving 260 cases, were reported during 2014 to 2016. Of all collected stool samples, 128 were positive for NoV including 6 of genogroupⅠ (GⅠ) and 122 of genogroupⅡ (GⅡ). All positive samples were genotyped into 6 genotypes, which were GⅡ.P17-GⅡ.17, GⅡ.P12-GⅡ.3, GⅡ.P7-GⅡ.6、GⅡ.P2-GⅡ.2, GⅠ.Pb-GⅠ.6 and GⅡ.Pg-GⅡ.12. The 23 outbreaks included both single infections and mixed genotype infections, which were 11 of GⅡ. 17 single infection, 4 of GⅡ. 3 single infection, 3 of GⅡ. 17 and GⅡ. 3 mixed infection, 2 of GⅡ. 17 and GⅡ. 6 mixed infection, 1 of GⅠ. 6 single infection, 1 of GⅡ. 17 and GⅡ. 2 mixed infection and 1 of GⅡ. 17 and GⅡ. 12 mixed infection. 
 
 
Conclusion 
NoV was an important pathogen responsible for viral diarrhea outbreaks in Qingdao. Several different genotypes were detected. The newly variant GⅡ.P17-GⅡ.17 was the predominant epidemic strain causing norovirus outbreaks in Qingdao during 2014 to 2016. 
 
 
Key words: 
Norovirus; Outbreak; Molecular epidemiology