1). The association of genetic and epidemiological/environmental factors as precursors for severe AVB by RSV has been reported in the literature. Certain risk factors are better known and are associated with disease severity, including prematurity,18 selleck products passive smoking,19

younger age,16 absence of breastfeeding,20 chronic lung disease, and congenital heart disease.21 However, other factors, such as genetic factors and other epidemiological data, show no evident confirmatory associations, and require further studies as markers of severity in AVB caused by RSV (Fig. 2). Prematurity, without the presence of bronchopulmonary dysplasia, has a seven-fold higher risk factor of AVB by RSV.18 A Brazilian study demonstrated that in 77 patients with AVB prematurity was associated with a higher probability of ICU admission, with an OR of 24.51 (95% CI: 3.21 to 186.92).16 In 230 infants age < 24 months, prematurity (gestational age < 37 weeks) was a risk factor for hospitalization.22 Among 284 patients admitted to the ICU for AVB, 30% were preterm.23 Another Brazilian cohort study of 5,301 children followed for a year showed that 113 were hospitalized for AVB, and the

risk of hospitalization was 80% higher in children whose mothers had pregnancies lasting less than 37 weeks.7 Prematurity in patients with AVB Anti-cancer Compound Library by RSV was also associated with increased risk of hypoxemia and respiratory failure requiring mechanical ventilation.24 In a retrospective

analysis of 4,800 infants hospitalized for AVB, it was concluded that prematurity and positive RSV represented risk factors for disease severity.25 In the assessment of 378 hospitalized patients with AVB, passive smoking was a risk factor for need for supplemental oxygen and mechanical ventilation,19 and in another sample of 240 children hospitalized for AVB, it was observed that passive smoking was associated with greater clinical severity and longer hospitalization.26 Demeclocycline In a meta-analysis that included 60 studies, passive smoking was a significant risk factor for AVB.27 In a prospective analysis of 206 patients hospitalized for AVB by RSV, children exposed to postnatal maternal smoking had lower levels of hemoglobin oxygen saturation than those not exposed (89.8% versus 92.2%, p = 0.01). 28 In Brazil, it was demonstrated that the risk of hospitalization for AVB was 57% higher in children exposed to maternal smoking than those not exposed. 7 It has been well established in the literature that the younger the child, the greater the clinical severity of AVB by RSV. In a Brazilian study, age had an OR of 0.838 (95% CI: 0.718-0.979) compared to hospitalization, indicating that older age was associated with a lower incidence of hospitalization.16 Patients younger than 2 months had a longer length of hospital stay (6 versus 5 days, p < 0.