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Respiratory syncytial virus (RSV) is a large, enveloped, nonsegmented, negative-strand RNA virus of the genus Pneumovirus of the family Paramyxoviridae. The virus uses attachment (G) and fusion (F) surface glycoproteins for virus entry. Two major strains (groups A and B) have been identified and often circulate concurrently.


Almost all children are infected at least once by 2 years of age. Humans are the only source of infection. Initial infection occurs most commonly during the child’s first year. Reinfection throughout life is common. In the United States, RSV occurs in annual epidemics during winter and early spring (predominantly November through March). Communities in the southern United States, particularly some communities in the state of Florida, tend to experience the earliest onset of RSV activity (as early as July). In the southern hemisphere, wintertime epidemics occur from May to September, with a peak in May, June, or July. RSV is the most common cause of acute lower respiratory tract infection (ALRI) in children <1 year of age. RSV is associated with up to 120,000 pediatric hospitalizations (1%–3% of children in the first 12 months of life) each year in the United States. Globally, the annual rate of RSV hospitalization among children <5 years is approximately 4.4 per 1000; hospitalization rates are highest among children <6 months old (2%) and premature infants <1 year old (6.4%). In addition, RSV is a common cause of nosocomial infection in the neonatal intensive care unit (NICU). It can persist on environmental surfaces for several hours and for a half-hour or more on hands. Infection among hospital personnel and others may occur by hand-to-eye or hand-to-nasal epithelium self-inoculation with contaminated secretions.


The disease is generally limited to the respiratory tract. RSV usually is transmitted by direct or close contact with contaminated secretions, which may occur from exposure to large-particle droplets at short distances (typically <6 feet) or from fomites. The inoculation of the virus occurs in nasopharyngeal or ocular mucous membranes after contact with virus-containing secretions or fomites. The virus replicates in the nasopharynx and spreads to the small bronchiolar epithelium, sparing the basal cells. Subsequently, the virus extends to type 1 and 2 alveolar pneumocytes in the lung, presumably by cell-to-cell spread or via aspiration of secretions. In infants, the disease manifests itself as bronchiolitis or pneumonia. In very rare cases, RSV may be recovered from extrapulmonary tissues, such as liver, spinal, or pericardial fluid. Up to 30% of children with RSV bronchiolitis may be coinfected with another respiratory tract virus, such as human metapneumovirus, rhinovirus, bocavirus, adenovirus, coronavirus, influenza virus, or parainfluenza virus.


Risk factors for RSV ALRI include infants <6 months of age, premature infants born <35 weeks’ gestation, infants with underlying lung disease such as chronic lung disease (CLD) of prematurity, infants ...

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