Changing pattern of rotavirus G genotype distribution in Chiang Mai, Thailand from 2002 to 2004: decline of G9 and reemergence of G1 and G2.

Group A rotaviruses are the most common cause of acute viral diarrhea in humans and animals throughout the world. Previous surveillance studies of group A rotaviruses in Thailand indicated that the dominant types of rotaviruses were changing from time to time. During 2000 and 2001, the G9 rotavirus emerged as the most prevalent genotype, with an exceptionally high frequency (91.6%) in Chiang Mai, Thailand. In the year 2002-2004, group A rotavirus was detected in 98 out of 263 (37.3%) fecal specimens collected from children hospitalized with diarrhea. Of these, 40 (40.8%) were G9P[8], 33 (33.7%) were G1P[8], 23 (23.5%) were G2P[4], and 2 (2.0%) were G3P[9]. The G9P[8] was found to be the most predominant strain in 2002, but the prevalence rate abruptly decreased during the period 2003-2004. In addition, G2P[4] reemerged in the epidemic season of 2003, whereas G1P[8] became the most predominant strain in the following year (2004). Phylogenetic analysis of the VP7 genes revealed that G1, G2, and G9 rotavirus strains clustered together with recently circulating strains, which were isolated from different regional settings in Thailand. In conclusion, the study demonstrated a decrease of incidence of G9P[8] and reemergence of G1P[8] and G2P[4] rotaviruses in Chiang Mai, Thailand during the period 2002-2004. These data imply that the distribution of group A rotavirus genotypes circulating in Chiang Mai, Thailand, changes over time.