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Respiratory Syncytial Virus (RSV) and Human Metapneumovirus Infections

by Mary T. Caserta, MD

Respiratory syncytial virus and human metapneumovirus infections cause seasonal lower respiratory tract disease, particularly in infants and young children. Disease may be asymptomatic, mild, or severe, including bronchiolitis and pneumonia. Although diagnosis is usually clinical, laboratory diagnosis is available. Treatment is supportive.

Respiratory syncytial virus (RSV) is an RNA virus, classified as a pneumovirus. Subgroups A and B have been identified. RSV is ubiquitous; almost all children are infected by age 4 yr. Outbreaks occur annually in winter or early spring in temperate climates. Because the immune response to RSV does not protect against reinfection, the attack rate is about 40% for all exposed people. However, antibody to RSV decreases illness severity. RSV is the most common cause of lower respiratory tract illness in young infants and is responsible for >50,000 hospitalizations annually in the US in children under the age of 5 yr.

Human metapneumovirus (hMPV) is a similar but separate virus. The seasonal epidemiology of hMPV appears to be similar to that of RSV, but the incidence of infection and illness appears to be substantially lower.

Symptoms and Signs

RSV and hMPV illness manifest similarly. The most recognizable clinical syndromes are bronchiolitis (see Bronchiolitis) and pneumonia (see Overview of Pneumonia). These illnesses typically begin with upper respiratory symptoms and fever, then progress over several days to dyspnea, cough, wheezing, and/or crackles on chest auscultation. Apnea may be the initial symptom of RSV in infants < 6 mo. In healthy adults and older children, illness is usually mild and may be inapparent or manifested only as an afebrile common cold. However, severe disease may develop in the following:

  • Patients who are < 6 mo, elderly, or immunocompromised

  • Patients who have underlying cardiopulmonary disorders


  • Clinical evaluation

  • Sometimes rapid antigen tests of nasal washings or swabs, reverse-transcription–PCR (RT-PCR), or viral culture

RSV (and possibly hMPV) infection is suspected in infants and young children with bronchiolitis or pneumonia during RSV season. Because antiviral treatment is not typically recommended, a specific laboratory diagnosis is unnecessary for patient management. However, a laboratory diagnosis may facilitate hospital infection control by allowing segregation of children infected with the same virus. Rapid antigen tests with high sensitivities for RSV and other respiratory viruses are available for use in children; nasal washings or swabs are used. These tests are less sensitive in adults. Molecular diagnostic assays such as RT-PCR have improved sensitivity and are generally available as single or multiplex assays.


  • Supportive care

Treatment of RSV and hMPV infections is supportive and includes supplemental O 2 and hydration as needed (see Bronchiolitis).

Corticosteroids and bronchodilators are generally not helpful and are currently not recommended.

Antibiotics are reserved for patients with fever, evidence of pneumonia on chest x-ray, and clinical suspicion of a bacterial coinfection.

Palivizumab (monoclonal antibody to RSV) is not effective for treatment.

Inhaled ribavirin, an antiviral drug with activity against RSV, has marginal efficacy, is potentially toxic to health care practitioners, and is no longer recommended except for infection in severely immunocompromised patients.


Contact precautions (eg, hand washing, gloves, isolation) are important, particularly in hospitals.

Passive prophylaxis with palivizumab decreases the frequency of hospitalization for RSV in high-risk infants. It is cost-effective only for infants at high risk of hospitalization, including those who

  • Are < 1 yr with hemodynamically significant congenital heart disease

  • Are < 1 yr with chronic lung disease of prematurity (gestational age < 32 wk and 0 days with the need for O 2 therapy for at least 28 days after birth)

  • Are born at < 29 wk gestation and are < 1 yr old at the start of RSV season

  • Have chronic lung disease of prematurity in the 2nd yr of life and have received treatment (chronic corticosteroid or diuretic treatment or continued need for O 2 therapy) within 6 mo of RSV season

Prophylaxis may also be considered for

  • Infants in the 1st yr of life who have anatomic pulmonary abnormalities that impair the ability to effectively clear the upper airways

  • Infants who have neuromuscular disorders

  • Children < 24 mo who have profound immunocompromise

The dose of palivizumab is 15 mg/kg IM. The first dose is given just before the usual onset of the RSV season (early November in North America). Subsequent doses are given at 1-mo intervals for the duration of the RSV season (usually a total of 5 doses).

Key Points

  • RSV and hMPV usually cause a syndrome of bronchiolitis, but pneumonia may occur.

  • Diagnosis is usually clinical, but testing, including rapid antigen tests and molecular assays (eg, PCR), is available.

  • Give supportive treatment; corticosteroids, bronchodilators, and palivizumab are not recommended.

  • Inhaled ribavirin may be useful for RSV but only in severely immunocompromised patients.

  • Passive prophylaxis with palivizumab just before and during RSV season decreases the frequency of hospitalization in high-risk infants.

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