Identification of novel norovirus polymerase genotypes from pediatric fecal samples collected between the year 1997 and 2000 in Japan.

We analyzed 46 pediatric fecal samples collected between the years 1997 and 2000 to retrospectively evaluate the norovirus strains circulating during that era and to identify possible re-emergence patterns. From the tested fecal samples, we detected GII.1, GII.3, GII.4 (95/96-US) and GII.6 strains. Most importantly, two novel polymerase genotypes (GI.PNA4 and GII.PNA7) were detected during the study. Two possible recombinant strains (GII.6[P7] and GII.3[P29]) were identified and SimPlot analysis confirmed that GII.6[P7] is a recombinant strain. The study emphasizes the importance of retrospective evaluation of human fecal samples in obtaining a better understanding of norovirus circulation, re-emergence and evolution.