The biennial cycle of respiratory syncytial virus outbreaks in Croatia

Abstract

The paper analyses the epidemic pattern of respiratory syncytial virus (RSV) outbreaks in children in Croatia. Over a period of 11 consecutive winter seasons (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) 3,435 inpatients from Zagreb County aged from infancy to 10 years who were hospitalised with acute respiratory tract infections were tested for RSV-infection. RSV was identified in nasopharyngeal secretions of patients by virus isolation in cell culture and by detection of viral antigen with monoclonal antibodies.In the Zagreb area, RSV outbreaks were proven to vary in a two-year cycle, which was repeated every 23-25 months. This biennial cycle comprised one larger and one smaller season. Climate factors correlated significantly with the number of RSV cases identified only in the large seasons, which suggests that the biennial cycle is likely to continue regardless of meteorological conditions. Knowledge of this biennial pattern should be useful in predicting the onset of RSV outbreaks in Croatia, and would facilitate planning for the prevention and control of RSV infections in the region. FindingsRespiratory syncytial virus (RSV) frequently causes acute respiratory tract infections (ARTI) among children. In investigations of the epidemiology of viral respiratory infections in Croatian children over four seasons in the 1980s, RSV was determined to be the agent of 20-34% of inpatient ARTI [1,2]. Our study of RSV-genotypes circulating in Zagreb and Vienna from 1987-1994 showed that they were similar to the pattern of expression of these genotypes globally [3].In temperate climates, RSV infections occur in winter and in the early spring [1,4]. The role of climate in causing this epidemic pattern has not been evaluated in the area including and surrounding Croatia. We set out to examine the timing of RSV epidemics and the relationship of various meteorological factors and the number of RSV infections in children over 11 consecutive years in Zagreb County. The county covers an area of 3,719.355 km 2 , and includes a population of 1,088,841 inhabitants in the northwest part of Croatia.

Seasonal Occurrence of Human Metapneumovirus Infections in Croatia

“…This cycle has been monitored over 17 consecutive years (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), and it was proved that the cycle repeats every 23-25 months and comprises 1 large or early and 1 small or late season. [26][27][28] Authors from Austria showed that HMPV outbreaks are also characterized by a biennial rhythm, with a strong peak of HMPV activity in late spring-summer months every second year. 13,17 In addition, they showed that HMPV outbreaks may overlap with RSV epidemics, but also can precede or follow annual RSV outbreaks.…”

Respiratory syncytial virus infection in infants and correlation with meteorological factors and air pollutants

“…A study performed in Croatia [15] presented a biennial cycle of RSV outbreaks with one large and one small season; the correlation between RSV epidemic and climatic factors was observed only for the larger season.…”

Eleven consecutive years of respiratory syncytial virus outbreaks in Croatia

“…In the first investigation of the epidemiology of viral infections in Croatia in the 1980s, RSV was determined to be the cause of bronchiolitis in 56.7% of infants up to 12 months of age 2 . Further investigation found that RSV infection in Croatia occurred in a biannual cycle 3 . The aim of the present study was to re‐analyze the epidemiologic pattern of RSV outbreaks in Croatian children over the past 11 years.…”