title: Does the viral subtype influence the biennial cycle of respiratory syncytial virus?
abstract: BACKGROUND
  The epidemic pattern of respiratory syncytial virus (RSV) is quite different in regions of Europe (biennial epidemics in alternating cycles of approximately 9 and 15 months) than in the Western Hemisphere (annual epidemics). In order to determine if these differences are accounted for by the circulation of different RSV subtypes, we studied the prevalence of RSV subtype A and B strains in Zagreb County from 1 January 2006 to 31 December 2007.
  
  
  RESULTS
  RSV was identified in the nasopharyngeal secretions of 368 inpatients using direct fluorescence assays and/or by virus isolation in cell culture. The subtype of recovered strains was determined by real-time PCR. Of 368 RSV infections identified in children during this interval, subtype A virus caused 94 infections, and subtype B 270. Four patients had a dual RSV infection (subtypes A and B). The period of study was characterized by two epidemic waves of RSV infections-one, smaller, in the spring of 2006 (peaking in March), the second, larger, in December 2006/January 2007 (peaking in January). The predominant subtype in both outbreaks was RSV subtype B. Not until November 2007 did RSV subtype A predominate, while initiating a new outbreak continuing into the following calendar year.
  
  
  CONCLUSIONS
  Though only two calendar years were monitored, we believe that the biennial RSV cycle in Croatia occurs independently of the dominant viral subtype.
authors.affiliation: Department of Virology, Croatian National Institute of Public Health and University Medical School of Zagreb, Zagreb, Croatia. gordana.galinovic@hzjz.hr
authors.forename: Gordana
authors.initials: G
authors.lastname: Mlinaric-Galinovic
authors.forename: Gordana
authors.initials: G
authors.lastname: Vojnovic
authors.forename: Jasna
authors.initials: J
authors.lastname: Cepin-Bogovic
authors.forename: Ana
authors.initials: A
authors.lastname: Bace
authors.forename: Jadranka
authors.initials: J
authors.lastname: Bozikov
authors.forename: Robert C
authors.initials: RC
authors.lastname: Welliver
authors.forename: Ulrich
authors.initials: U
authors.lastname: Wahn
authors.forename: Ljiljana
authors.initials: L
authors.lastname: Cebalo
mesh_terms: D002648:Child; D002675:Child, Preschool; D017523:Croatia / Q000453:epidemiology; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology* / Q000821:virology*; D012136:Respiratory Syncytial Viruses / Q000235:genetics* / Q000302:isolation & purification