Molecular epidemiology of respiratory syncytial virus

Objective To determine the epidemiologic pattern of subgroups A and B and g enotypes of respiratory syncytial virus (RSV) during two noncontinuous epid emics during 1990-1991 and 1997-1998 in Beijing. Methods Nasopharyngeal secretion (NPS) samples ol RSV positive or RSV isola tes tested by indirect immunofluorescence (IIF) assay were classified into subgroups A and B. Isolates of RSV were divided into at least six different lineages, designated NP1-NP6, by restriction mapping of the N gene. Np1, 3 and 6 were given by subgroup B isolates, while NP2, 4 and 5 were given by subgroup A isolates. Strains of subgroup A were further subdivided into six lineages SHL1-SHL6 on the basis of the SH gene sequence. SH lineages were closely related to each other and to NP1-NP6. Strains of SHL1, 3 and 4 were closely related and belonged to NP2, SHL2 and 6 to NP4, and SHL5 to NP5. Results Of 145 RSV NPS samples from the 1997-1998 epidemic, 83 (57.2%) were of subgroup B RSV positive, 62 (42.8%) of subgroup A RSV positive. The rat e of occurrence of subgroup A to B strains was about 1:1.3. Two of 10 isola tes during the epidemic were subgroup A strains, whereas 8 were subgroup B strains. The rate of occurrence of subgroup A to B strains was 1.4. Eight s ubgroup A strains of 10 isolates from the 1990-1991 epidemic were dominant; the proportion of subgroup A to B strains was 4:1. With 10 RSV isolates in 1997-1998, all 2 subgroup A strains gave N gene fragment restriction patte rn NP4, and fell into SH lineage SHL2, whereas 8 subgroup B strains all bel onged to NP3. All 8 subgroup A isolates from the 1990-1991 epidemic gave pa ttern NP4, and fell into SHL2, while 2 subgroup B strains all belonged to N P3. The classification of subgroups A and B deduced from NP patterns corres ponded to the definition of these subgroups by monoclonal antibodies. Conclusions These observations confirm that subgroups A and B or multiple l ineages of RSV cocirculated in Beijing, but different genome types predomin ated each year. Moreover, very similar viruses were isolated up to more tha n 5 years ago, indicating that despite apparent diversity of the subgroup A strains, the separate lineages might be relatively stable.