9 The first infections are usually symptomatic and often affect the lower airways; subsequent infections are usually milder. RSV is the agent responsible for AVB in 41.7%10 to 83.6% of cases.11 In Brazil, RSV was responsible for 31.9%12 to 64% of hospitalized patients with AVB.13 Although other viruses are detected in patients with AVB, such as adenovirus, bocavirus, Influenza A, Influenza B, Parainfluenza virus 1, Parainfluenza virus 2, Parainfluenza virus 3, rhinovirus, and metapneumovirus, 10 and 11 the establishment of codetection or coinfection

has been a critical Tariquidar solubility dmso aspect yet to be considered. 14 The second most common virus in AVB is the rhinovirus, corresponding to approximately 18% of cases. 15 In Brazil, it was found that viral coinfection occurs in 40% of AVB cases and that the most common virus after RSV is the rhinovirus, occurring in 40% of cases. 16 Epidemiological factors associated with the severity of AVB by RSV are known and have been reported in the literature; however, some children with severe AVB do not have any of these risk factors (Table 1). In this regard, recent studies have assessed the influence of genetic factors related to disease severity (Table 2). Due to the possibility of AVB evolving into a more severe form, it becomes important

to identify genetic and environmental VX-809 price risk factors that can contribute to its greater severity. Recently, several studies have

led to the creation of guidelines around the world, showing that children at high risk of acquiring severe RSV infection should receive passive immunization with monoclonal antibody against RSV (palivizumab), which promotes protection against severe forms of the disease. After the introduction of palivizumab, a 48% reduction in hospitalizations of infants with chronic lung disease of prematurity was observed.17 A vaccine aimed at preventing AVB by RSV has yet to be developed, despite efforts in this regard since the 1960s.1 The objective of this review was to evaluate the epidemiological and genetic factors that contribute to the severity of AVB by RSV, allowing for better patient management and prediction of RNA Synthesis inhibitor risk groups associated with the disease, decreasing costs for the health system, and allowing for a reduction in the number of hospitalizations and deaths. The key words “bronchiolitis”, “risk factor”, “genetics”, and “respiratory syncytial virus” and all their combinations were used in a search conducted at the PubMed (http://www.ncbi.nlm.nih.gov/pubmed), SciELO (http://www.scielo.org/php/index.php), and LILACS (http://lilacs.bvsalud.org/en/) databases of articles published after the year 2000 that included individuals younger than 2 years old. The last search was performed in October of 2012. A total of 1,259 articles were found, of which all abstracts were read.