DESCRIPTION

• An enveloped, nonsegmented RNA virus of the family Paramyxoviridae and in the subfamily Pneumovirinae along with human metapneumovirus. There are 2 subgroups, A and B, differentiated by the major attachment G protein, a large surface glycoprotein. The fusion or F protein is relatively homologous between the 2 subgroups.
• It is the most common cause of bronchiolitis, a lower respiratory tract disease that primarily affects the small airways.

EPIDEMIOLOGY

• Incubation period is 2 to 8 days.
• Virus is detected in secretions 4 days prior to clinical symptoms. Typically shedding of infectious virions is 3 to 8 days but can be as long as 3 to 4 weeks in immunocompromised.
• Transmission occurs by direct contact of nasopharyngeal or ocular mucosa with infected secretions or fomites.
• Nosocomial spread can occur because the virus can survive on surfaces for several hours and hands for 30 minutes or more.
• In the United States, epidemics typically occur between November and April and last for roughly 18 to 20 weeks.
• In tropical climates, respiratory syncytial virus (RSV) seasons are less predictable and can circulate year-round.
• There was a dramatic decrease in RSV infections from May 2020 to March 2021, likely due to changes in epidemiology patterns with the adoption of measures to reduce the spread of COVID-19.
• This was followed by a deviation in the typical seasonality of the virus. One antigenic strain predominates during any given epidemic, but both subtypes can circulate concurrently.

RISK FACTORS

Those at greatest risk for severe infection include the following:

• Children <1 year of age, especially those <6 months of age
• Children born prematurely (<35 weeks’ gestation)
• Children with underlying cardiopulmonary disease (e.g., chronic lung disease of prematurity, congenital heart disease)
• Those with primary immune deficits
• Patients on immunosuppressive medications (e.g., transplant patients, oncology patients)

GENERAL PREVENTION

• Because RSV can survive on surfaces, strict hand washing can minimize nosocomial spread.
• Contact isolation with routine usage of gowns and gloves has been shown to decrease RSV nosocomial spread.
• Patients with RSV infection should be isolated in private rooms or cohorted.
• Vaccines
  • In May 2023, two RSV vaccines were approved by the U.S. Food and Drug Administration (FDA) for use in older adults, both containing prefusion RSV F glycoproteins, one adjuvanted (Arexvy^®), the other nonadjuvanted (Abrysvo^®).
  • The latter is recommended for use in pregnant women between 32 0/7 weeks’ and 36 0/7 weeks’ gestation to promote RSV antibody transfer that will protect neonates and young infants.
• Nirsevimab (Beyfortus^®) is a human monoclonal antibody against the RSV fusion protein with an extended half-life that can potentially cover an entire RSV season.
  • Approved for medical use in the United States in July 2023
  • Indicated for neonates and infants born during or entering their first RSV season and in children up to 24 months of age who remain vulnerable to severe RSV through their second season.
• Palivizumab (Synagis^®), a humanized monoclonal antibody directed against the highly conserved F protein of RSV
  • Children who should receive palivizumab:
    • Infants born before 29 weeks’ gestation
    • Preterm infants with chronic lung disease of prematurity. In these children, palivizumab should also be given during the 2nd year of life if they are receiving medical therapy (e.g., oxygen, chronic corticosteroids, or diuretics) for chronic lung disease.
  • Children for whom palivizumab should be considered:
    • Infants with hemodynamically significant congenital heart disease, anatomic pulmonary abnormalities, or neuromuscular disease
    • Children <24 months of age who will be profoundly immunocompromised during RSV season
  • Palivizumab is given IM (15 mg/kg) every 30 days for a maximum of 5 doses during RSV season (usually from October/November to March/April).
  • Palivizumab prophylaxis should be discontinued if a patient experiences a breakthrough RSV hospitalization due to the low likelihood of another RSV hospitalization in the same season.
  • Specific recommendations (last updated in 2014) are available from the American Academy of Pediatrics (AAP).
  • Of note, with the shift in RSV seasonality noted in 2021, the AAP provided interim guidance supporting the use of palivizumab in eligible infants in areas experiencing increased RSV circulation at any time in 2022.

PATHOPHYSIOLOGY

• The G protein is the major surface glycoprotein responsible for attachment of virus to cells.
• The F protein aids in viral entry into cells and is responsible for fusion of adjacent cells to form a syncytia.
• Infection is initiated in nasopharynx and then can move to the lower respiratory tract.
• Infection of smaller airways leads to edema and necrosis of epithelial cells and infiltration of inflammatory cells, resulting in airway obstruction and air trapping.
• Severe RSV infection has been associated with recurrent wheezing later in life. It is unclear whether RSV infection causes subsequent wheezing or if patients predisposed to severe wheezing are more likely to have severe RSV disease.