Analysis of biennial outbreak pattern of respiratory syncytial virus according to subtype (A and B) in the Zagreb region.
BACKGROUND
The epidemic pattern of respiratory syncytial virus (RSV) in Croatia is biennial. In order to determine if the circulation of different RSV subtypes affects the outbreak cycle, the aim of the present study was to analyze the epidemic pattern of RSV in children in Croatia (Zagreb region) over a period of 3 consecutive years.


METHODS
The study group consisted of 696 inpatients, aged 0-5 years, who were hospitalized with acute respiratory tract infections caused by RSV, in Zagreb, in the period 1 January 2006-31 December 2008. The virus was identified in nasopharyngeal secretions using direct immunofluorescence. The virus subtype was determined on real-time polymerase chain reaction.


RESULTS
Of 696 RSV infections identified in children, subtype A virus caused 374 infections, and subtype B, 318. Four patients had a dual RSV infection (subtypes A and B). The period of study was characterized by four epidemic waves of RSV infections: the first, smaller, in the spring of 2006; the second, larger, in December 2006/January 2007; the third in spring 2008, followed by a fourth outbreak beginning in November of 2008. The biennial virus cycles were persistent although the predominant RSV subtype in the first two epidemic waves was subtype B, and in the second two it was subtype A.


CONCLUSIONS
Over a 3 year period of observation, the biennial RSV cycle in Croatia cannot be explained by a difference in the predominant circulating subtype of RSV. Other unknown factors account for the biennial cycle of RSV epidemics in Croatia.
Department of Virology, Croatian National Institute of Public Health and University Medical School of Zagreb, Zagreb, Croatia. gordana.galinovic@hzjz.hr
Gordana
G
Mlinaric-Galinovic
Irena
I
Tabain
Tamara
T
Kukovec
Gordana
G
Vojnovic
Jadranka
J
Bozikov
Jasna
J
Bogovic-Cepin
Irena
I
Ivkovic-Jurekovic
Ivica
I
Knezovic
Goran
G
Tesovic
Robert C
RC
Welliver
D002675:Child, Preschool; D017523:Croatia / Q000453:epidemiology; D004196:Disease Outbreaks; D006801:Humans; D007223:Infant; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology*; D018113:Respiratory Syncytial Virus, Human / Q000145:classification*; D012621:Seasons