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[Study on typing of respiratory syncytial viruses].

OBJECTIVE
To determine the epidemiologic patterns of subgroups A and B and genotypes of respiratory syncytial viruses (RSV) during two uncontinuously epidemic years from 1990 to 1991 and 1997 to 1998 in Beijing.


METHODS
Nasopharyngeal secretion (NPS) samples of RSV positive or BSV isolates tested by indirect immunofluorescent (IIF) assay were classified into subgroups A and B. Also, isolates of RSV were divided into at least six different lineages, designated NPl-6, by restriction mapping of the N gene. NP l, 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 SHL 1-6 on the basis of the SH gene sequence. SH lineages were closely related to each other and to NP 1-6. Strains of SHL 1,3, and 4 were closely related and belonged to NP2, SHL 2 and 6 to NP4 and SHL5 to NP5.


RESULTS
Of 145 RSV NPS samples from the winter 1997 to the spring 1998, 83(57.2%) were subgroup B strains, 62(42.8%) were sub-group A strains, the rate of occurrence of subgroup A to B strains was about 1:1.3. Two of 10 isolates of 1997-1998 offered by viral department of research institute of Pediatrics were subgroup A strains, whereas 8 were subgroup B strains, the rate of occurrence of subgroup A to B strains was 1:4. Eight subgroup A strains of 10 isolates from the 1990-1991 epidemic were dominant, the proportion of subgroup A to B strains was 4:1. of 10 BSV isolates in 1997-1998, all 2 subgroups A strains gave N gene fragment restriction pattern NP4, and fell into SH lineage SHL2, whereas 8 subgroup B strains all belonged to NP3. All 8 subgroup A isolates from the 1990-1991 epidemic gave pattern NP4, and fell into SHL2, while 2 subgroups B strains all belonged to NP3. The classification of subgroups A and B deduced from NP patterns was corresponded to the definition of these subgroups by monoclonal antibodies.


CONCLUSIONS
These observations confirmed that subgroups A and B or multiple lineages of BSV co-circulated in Beijing, but different genomic types predominated each year. Moreover, very similar viruses were isolated up to more than 5 years ago, indicating that despite apparent diversity of the subgroup A strains, the separate lineages might be relatively stable.