DETECTION AND CHARACTERIZATION OF NOVEL ROTAVIRUS STRAINS IN THE UNITED-STATES

We recently established a rotavirus strain surveillance system in the United States to monitor the prevalent G serotypes before and after th e anticipated implementation of a vaccination program against rotaviru s and to identify the emergence of uncommon strains. In this study, we examined 348 rotavirus strains obtained in 1996 to 1997 from children with diarrhea in 10 U.S. cities. Strains were characterized for P and G types, subgroups, and electropherotypes by using a combination of m onoclonal antibody immunoassay, reverse transcription-PCR, and hybridi zation. The four strains most commonly found worldwide comprised 83% o f the isolates (P[8]G1, 66.4%; P[4]G2, 8.3%; P[8]G3, 6.9%; P[8]G4, 1.4 %), but 9.2% were unusual strains (P[6]G9, 5.5%; P[8]G9, 1.7%; P[6]G1, 1.4%; and P[4]G1 and P[8]G2, 0.3% each). Strains not typeable for P o r G type accounted for 5.5% of the total, while 2.3% of the strains ha d more than one G type (mixed infections). All P[6] G9 strains tested had short electropherotypes and subgroup I specificity and were detect ed in 4 of 10 cities, while P[8] G9 strains had long electropherotypes and subgroup II VP6 antigens. Both sequence analysis of the VP7 open reading frame (about 94 to 95% amino acid identity with the VP7 gene o f G9 prototype strain W161) and binding to a G9 specific monoclonal an tibody strongly suggest that U.S. Go strains belong to serotype G9. Th e high detection rates of unusual rotaviruses with G9 (7.2%) or P[6] ( 6.9%) specificity in multiple U.S. cities suggest the emergence of new strains or inadequate diagnosis in the past. The epidemiologic import ance of these strains remains to be determined.