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Over 15 years respiratory syncytial virus (RSV) isolates from 1209 hospitalized and ambulatory children were examined for strain group and in a subset for subgroup to determine the associated epidemiologic and clinical characteristics. Three patterns of yearly outbreaks existed: (1) strong predominance of group A strains (9 years with 83%-100% A strains), (2) relatively equal proportions of group A and B strains (4 years), and (3) strong predominance of group B strains (78%-85%) in 2 years, separated by a decade. The first pattern of highly dominant A strains occurred in cycles of 1 or 2 consecutive years with a single intervening year in which B strains were greater than or equal to 40% of the isolates. Subgroups A1 and A2 predominated, while B2, 3, and 4 occurred almost equally. A greater clinical severity for Group A strains was suggested by children with group A infections requiring intensive care significantly more often (15.4 vs. 8.3%, P = .008). Further, strongly dominant A strain years were associated with higher proportions of RSV admissions requiring intensive care (16.6% vs. 5.5%, P less than .01). Strains of subgroups A2 and B4 were more frequently found in hospitalized patients and A1 in outpatients, and the 2 years with the highest rates of intensive care admissions were those in which subgroup A2 dominated.
Hall et al. (Sat,) studied this question.