Respiratory syncytial virus (RSV) is one of the main causes of acute respiratory infection (ARI) among infants and the elderly. This virus is particularly associated to the admission into intensive care units in children under the age of two years, who develop either influenza-like illness (ILI) or severe acute respiratory infection (SARI).1-3 Environments with low humidity and high temperatures favor the survival of RSV virions, while during the winter or rainy seasons, the number of infections increases, since more people remain indoors.4, 5 In temperate zones, this virus has seasonal transmission with onsets matching the coldest weeks of winter.1, 6, 7 In equatorial countries, RSV is involved in ARI cases all year round, with outbreaks in those rainy seasons of high humidity and low temperature.

RSV has been classified in two types (RSV-A and RSV-B), based on genetic differences in the region encoding glycoprotein G, a protein that facilitates binding of the virus to epithelial cells of the airway.7 10 New RSV genotypes arise by mutations and duplications in the glycoprotein G gene and spread according to their antigenicity and virulence; these properties are also influenced by substitutions in the fusion protein.

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