Norovirus (NoV) is a leading cause of diarrhea inpatients of all age groups with acute gastroenteritis worldwide [1]. Starting in November 2014, Guangdong [2], Jiangsu [3], and Zhejiang [4] in China, and Japan [5] reported diarrheal disease outbreaks that were caused by a novel NoV genotype GII.17. Chen et al. [6] reported this novel genotype collected from sporadic patients in Shanghai during the winter of 2014–2015 has evolutionary relationships with other reported genotypes [2, 5]. Here, we characterized the molecular epidemiology of NoV infections in Shanghai between July 2014 and June 2015 to examine when did this novel NoV genotype strain begin to prevalent and whether the NoV GII.4 is still the leading NoV genotype in Shanghai, China.

A total of 2169 stool samples were collected from 18,669 diarrheal patients, reported to the syndromic surveillance network from 12 sentinel hospitals, between July 2014 and June 2015. The detection rate of the NoV GI and GII was 0.83% (18/2169) and 24.02% (521/2169) by real-time reverse transcription polymerase chain reaction (qRT-PCR), respectively.

Partial nucleotide sequences of the NoV GII ORF2 gene was amplified. Genotypes were determined using Norovirus Genotyping Tool Version 1.0. The numbers of strains corresponding to the GII.2, GII.3, GII.4, GII.6, GII.13, GII.17 and GII.21 strains were 3, 5, 133, 3, 8, 286 and 10, respectively. GII.17 (63.84%, 286/448) and GII.4 (29.69%, 133/448) were the most prevalent NoV GII genotypes between July 2014 and January 2015.

NoV infections occurred in all seasons and peaked between October 2014 and April 2015 (Fig. 1). The novel genotype GII.17 strain was first detected in a 24-year-old female patient on August 14th, 2014 in Shanghai. Beginning in January 2015, GII.17, which clustered to the novel variant Kawasaki_2014, was the most prevalent genotype of NoV GII, replacing GII.4 as the most prevalent NoV genotype in Shanghai. After May 2015, the GII.4 strain was rarely detected (Fig. 1).

Fig. 1
figure 1

Time distribution (month) of NoV genotypes with acute diarrheal in Shanghai, China, 2014–2015

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As the most prevalent strain, the GII.4 genotype Sydney_2012 and its variants were surveyed and reported globally [7–12], beginning in 2012 [13]. However, starting in November 2014, a novel NoV genotype GII.17 was reported to cause diarrheal disease outbreaks, worldwidely [2, 5, 14–16] and Matesushiam et al. [5] found that this novel genotype had a polymerase sequence and amino acid substitutions in the capsid region. In this study, we reported that the GII.17 genotype was first detected in diarrheal patients in August 2014, which was earlier than the first reported outbreak in Jiangsu [3]. Similar with the findings by Chen et al. [6], the GII.17 genotype became the predominant genotype beginning in November 2014 (Fig. 2). Our findings demonstrate that beginning in December 2014, GII.17 replaced GII.4 as the most prevalent NoV genotype in Shanghai. Teasing out viral, environmental, or host specific factors should be investigated to understand emergence of GII.17 [15] and ongoing surveillance should be performed to verify whether this novel genotype would be prevalent continuously.

Fig. 2
figure 2

Phylogenetic analysis of partial capsid region (ORF2) of NoV strains. Presented is a cladogram with supporting bootstrap values with full length VP1 nucleotide of reference NoVs according to LeBlanc et al. [15]. Representative strain from acute diarrheal patients in Shanghai, 2014–2015 are shown with black circle

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