The role of respiratory syncytial virus in influenzalike illness in the general population.

Background: Influenza is a major cause of morbidity and mortality in the human population. Influenza virus activity has been monitored by the European Influenza Surveillance Scheme (EISS) since 1996. A number of countries in EISS test clinical respiratory specimens for RSV in addition to influenza virus, as RSV infection causes similar symptoms as influenza virus infection. The aim of our study was to investigate the contribution of RSV in community cases of influenza-like illness (ILI). Methods: The study included data from the United Kingdom, France South, The Netherlands, and Scotland. Nose and/or throat swabs were obtained by sentinel physicians from patients with ILI during three winter seasons (2001–2002, 2002–2003, and 2003–2004). Methodological differences (e.g. in laboratory testing) had limitations for making country comparisons. The respiratory specimens were systematically tested for both influenza virus and RSV. Four age groups were analysed: 0–4, 5–14, 15–64, and 65þ. Results: The seasonal average prevalence of influenza positive specimens varied from 11.9% (5.2–20.4%) in Scotland to 28.3% (25.8– 30.2%) in France South. For RSV, the seasonal average prevalence varied from 1.5% (0.8–1.8%) in The Netherlands to 11.2% (4.3–26.7%) in the United Kingdom. The seasonal age specific data showed the following pattern for all four countries: influenza virus particularly affected the 5–14 age group, and RSV the 0–4 age group. The seasonal prevalence for RSV in the 0–4 age group varied from 9.6% (5.6–15.4%) in The Netherlands to 24.1% (15.2–40.8%) in the United Kingdom. Conclusions: RSV can be an important confounder in influenza surveillance, especially in ILI reports from very young children. Influenza surveillance systems should, when possible, also routinely test respiratory specimens for RSV.(aut.ref.)