Bronchiolitis is the most common lower respiratory tract infection in children younger than five years. Respiratory syncytial virus (RSV) is the most common viral cause of bronchiolitis worldwide. This article summarizes the best available evidence for the management of RSV bronchiolitis.

Epidemiology

• RSV is spread through respiratory droplets, with symptoms developing after an incubation period of four to six days.^1,2

• The global incidence of RSV bronchiolitis is estimated to be 8.1 cases per 1,000 children per year, leading to 33 million cases and 3.6 million hospitalizations in 2019.³ In the United States, the incidence of RSV-related hospitalizations in children younger than five years is estimated at 2.9 cases per 1,000 per year.⁴

• The incidence of RSV bronchiolitis varies with region and season. Before the COVID-19 pandemic, cases peaked between mid-October and May in the United States. Since COVID-19 restrictions were lifted, RSV peaks have been delayed to spring and summer.^1,5,6 The Centers for Disease Control and Prevention performs surveillance for RSV and reports weekly trends by region.⁷

• Age is the most important risk factor for severe disease and hospitalization. The rate of RSV- related hospitalization in infants younger than one month is estimated to be 25.1 per 1,000 (95% CI, 21.1 to 29.3). Infants born before 36 weeks of gestation are significantly more likely to need hospitalization compared with term infants.^1,4

• RSV is isolated in up to 83% of RSV cases. Viral coinfection occurs in up to 55% of cases, with human rhinovirus being the most common coisolate.⁸ A 2017 study over 12 epidemic seasons found that coinfection did not affect disease severity or outcomes.⁹

Prevention

• Standard precautions against the spread of respiratory droplets, such as hand hygiene, surface cleaning, and avoiding contact with sick individuals, are recommended.¹

• Prophylactic palivizumab, an intramuscular monoclonal antibody, may be considered for children at risk of severe infection (Table 1^1,2,10). Palivizumab is given monthly during RSV season, for up to five doses (15 mg per kg per dose). It should be discontinued if the child is subsequently hospitalized for RSV.^1,10,11

• A 2021 Cochrane review demonstrated that palivizumab leads to significantly fewer RSV hospitalizations (number needed to treat [NNT] = 18), but with no significant mortality benefit.¹¹

• One dose of nirsevimab at the start of RSV season has been shown decrease the need for outpatient evaluation (NNT = 14) and hospitalization (NNT = 30) in preterm infants (less than 35 weeks).¹² In healthy late preterm infants (35 to 37 weeks) and full-term infants, one dose of nirsevimab prevents outpatient visits (NNT = 26) and may prevent hospitalization; however, further study is needed.¹³ Nirsevimab has been approved by the U.S. Food and Drug Administration (FDA) and is expected to be available at the start of the fall 2023 RSV season.

• A recent phase 3 trial has shown that a single intramuscular dose of a bivalent RSV prefusion F vaccine given to pregnant patients between 24 and 36 weeks of gestation is 81.8% (99.5% CI, 40.6 to 96.3) effective in preventing medical evaluation for severe RSV in newborns through 90 days of life. The vaccine is 69.4% (97.59% CI, 44.3 to 84.1) effective through 180 days of life.¹⁴ The vaccine has been FDA-approved for high-risk children.