Recombinant GII.P16-GII.2 Norovirus, Taiwan, 2016

In Taiwan, acute gastroenteritis outbreaks caused by a new norovirus genotype GII.2 increased sharply toward the end of 2016. Unlike previous outbreaks, which often involved restaurants, GII.2 outbreaks mainly occurred in schools. Phylogenetic analysis indicates that these noroviruses are recombinant GII.P16-GII.2 strains.

In Taiwan, acute gastroenteritis outbreaks caused by a new norovirus genotype GII.2 increased sharply toward the end of 2016. Unlike previous outbreaks, which often involved restaurants, GII.2 outbreaks mainly occurred in schools. Phylogenetic analysis indicates that these noroviruses are recombinant GII.P16-GII.2 strains. N orovirus, the leading global cause of epidemic gastroenteritis, is responsible for >90% of all viral gastroenteritis and ≈50% of gastroenteritis outbreaks worldwide (1). In Taiwan, variants of the genotype GII.4 had been the most prevalent genotype in norovirus-associated acute gastroenteritis outbreaks until mid-2014 (2). Since winter 2014-15, a previously uncommon genotype, GII.17, became the predominant genotype in Taiwan. This GII.17 strain also caused many outbreaks in Japan and was reported sporadically in other parts of the world (3,4). Since September 2016, we have identified a new GII.P16-GII.2 strain that has replaced GII.17 as the predominant strain in norovirus-associated outbreaks in Taiwan, concurrent with a sharp increase in GII.P16-GII.2 norovirus outbreaks and sporadic cases during the 2016-17 season in Germany (5).

The Study
During January 2015-December 2016, a total of 876 acute gastroenteritis outbreaks were reported to the Centers for Disease Control in Taiwan. A total of 576 (65.8%) outbreaks were identified as norovirus by reverse transcription PCR with primer pairs G1SKF/G1SKR and G2SKF/ G2SKR for GI and GII genogroup detection, respectively; all positive samples underwent sequence-based genotyping by using the Norovirus Genotyping Tool (Table 1) (2,6,7). Before August 2016, GII.2 strains had been detected only sporadically ( Figure 1). By September 2016, GII.2 accounted for 60% of norovirus-associated acute gastroenteritis outbreaks that month and, in December 2016, for 86%. Globally, GII.2 is an uncommon genotype that accounted for ≈1.2% of sporadic norovirus infections in children during 2004-2012; by contrast, GII.4 was responsible for 67.2% of norovirus infections during the same period (8). In 2016, the settings of outbreaks involving GII.2 differed from those of non-GII.2; most (72.0%) GII.2 outbreaks occurred in schools, whereas most non-GII.2 outbreaks occurred in restaurants (41.4%) and fewer occurred in schools (31.0%). Within schools, half of GII.2 outbreaks occurred in kindergartens, 33.3% in elementary schools, and 14.9% in junior/senior high schools and colleges/universities ( Table 2).
Complete or near full-length open reading frame (ORF) 2 (viral protein [VP] 1) and partial ORF1 (RNA-dependent RNA polymerase [RdRp]) sequences were further obtained from 11 randomly selected Taiwan GII.2 2016 strains by different outbreak and month, as previously described (2). However, only 10 and 8 of the RdRp and VP1 sequences, respectively, were of sufficient quality and length for use in analysis. We identified the RdRp region of all GII.2 Taiwan strains as genotype GII.P16 (Figure 2, panel A). Phylogenetic trees were inferred from GII.P16 RdRp and GII.2 VP1 sequences, and in both trees, the GII.  (14). Recent 2016 GII.P16-GII.2 strains became the predominant strains of norovirus-associated acute gastroenteritis in Taiwan (Figure 1), although whether they were involved in outbreaks before 2004 is unknown because norovirus monitoring in Taiwan did not begin until that year. The recent outbreaks illustrated the potential of GII.2 to turn from a sporadically detected strain into an unprecedented dominating strain.

Conclusions
We report the previously uncommon norovirus genotype GII.P16-GII.2 causing an epidemic in Taiwan in late 2016. Previously, GII.2 strains were infrequently reported among both sporadic cases and outbreaks in Taiwan

World Hepatitis Day, July 28
Viral hepatitis-a group of infectious diseases known as hepatitis A, B, C, D, and E-affects millions of people worldwide, causing acute and chronic liver disease and killing close to 1.4 million people every year. Hepatitis remains largely ignored or unknown. Transmission of this virus can be prevented through better awareness and services that improve vaccinations, promote blood and injection safety, and reduce harm. On World Hepatitis Day, 28 July 2015, CDC, along with WHO and partners focused on the prevention of viral hepatitis to raise awareness among the general public and infected patients, but also to urgently promote improved access to hepatitis services, particularly prevention interventions, by policymakers.