eMedicine Specialties > Pediatrics: General Medicine > Infectious Disease

Respiratory Syncytial Virus (RSV) Infection

Author: Leonard R Krilov, MD, Chief of Pediatric Infectious Diseases, Vice Chair, Department of Pediatrics, Professor of Pediatrics, Winthrop University Hospital
Contributor Information and Disclosures

Updated: Feb 17, 2006

Introduction

Background

Respiratory syncytial virus (RSV) infection, which manifests primarily as bronchiolitis¹ and/or viral pneumonia, is the leading cause of lower respiratory tract (LRT) infection in infants and young children. The clinical entity of bronchiolitis was described at least 100 years ago. In 1956, Morris and colleagues initially isolated RSV from chimpanzees with upper respiratory tract (URT) infections as the causative agent of most epidemic bronchiolitis cases. Subsequently, Channock et al associated this agent with bronchiolitis and LRT infection in infants. Since then, multiple epidemiologic studies have confirmed the role of this virus as the leading cause of LRT infection in infants and young children.

Peak incidence of occurrence is observed at age 2-8 months. Overall, 4-5 million children younger than 4 years acquire an RSV infection, and more than 125,000 children are hospitalized annually in the United States because of this infection. This translates to 3-9 per 1000 children younger than 1 year who are hospitalized annually for this condition. Virtually all children have had at least one RSV infection by their third birthday. The World Health Organization has targeted RSV for vaccine development, which is not surprising, given the prevalence and potential severity of this condition. This article reviews aspects of the virology, epidemiology, spectrum of clinical illness, diagnosis, treatment, and prevention of RSV-related illness.

Pathophysiology

RSV infection is limited to the respiratory tract. Initial infection in young infants or children frequently involves the LRT and most often manifests as the clinical entity of bronchiolitis. This clinical syndrome has been recognized for at least 100 years. Inoculation of the virus occurs in the URT in respiratory epithelial cells. Spread of the virus down the respiratory tract occurs by cell-to-cell transfer of the virus along intracytoplasmic bridges (syncytia) from the URT to the LRT.

The illness may begin with URT symptoms and progress rapidly over 1-2 days to the development of diffuse small airway disease characterized by cough, coryza, wheezing and rales, low-grade fever (<101°F), and decreased oral intake. A family history of asthma and/or atopy is frequently obtained. In more advanced disease, retractions and cyanosis may be noted, and up to 20% of patients may develop higher temperatures. The incidence of concomitant or secondary serious bacterial infection in association with RSV infection appears to be quite low (<1%), except for otitis media, which may occur in up to 40% of cases. In very young infants, apnea out of proportion to respiratory signs and symptoms may be present, and, in infants younger than 6 weeks, a more nonspecific sepsislike picture has been described.²

Reinfection with RSV occurs at all ages; however, with recurrent infection and increasing age, RSV infections are more limited to the URT. RSV URT infection is more severe than the common cold, as evidenced by the 7- to 10-day duration of illness and by the finding in one study of adults with RSV that the mean absence from work is 6 days.

Frequency

United States

RSV LRT infection develops annually in 4-5 million children, and more than 125,000 children are admitted per year for RSV-related illness. Reinfection occurs throughout life, with the disease becoming limited to the URT in persons older than 3 years. Severe RSV disease has been reported in older children and adults with severe underlying immunodeficiency disorders (eg, bone marrow transplantation), and RSV LRT disease has been reported in elderly persons.

International

RSV infection is prevalent worldwide, with similar clinical manifestations and young age of RSV LRT infection.

Mortality/Morbidity

Even in children hospitalized with RSV infection, the mortality rate is less than 1%. However, in select groups of high-risk patients, appreciable mortality and increased morbidity still may occur from this infection.^3,4

• Infants with chronic lung disease of infancy (ie, bronchopulmonary dysplasia), congenital heart disease, or marked prematurity when hospitalized for this disease still may have a 3-5% mortality rate. Additionally, such infants and patients with immunodeficient states have been shown to spend, on average, twice as long in the hospital as other patients with RSV infection (7-8 d vs 3-4 d in normal full-term infants).
• Additionally, children hospitalized for RSV disease during infancy have been shown to have abnormal pulmonary function tests and/or increased episodes of wheezing up to 10 years later. Whether RSV itself plays an active role in this or is just a marker for children at risk for reactive airway disease remains controversial.

Race

All races appear susceptible to RSV, with similar disease patterns.

Sex

Although boys and girls are affected equally by milder RSV disease, the frequency of hospitalization for RSV disease is higher in males, with a male-female-ratio of approximately 2:1.

Age

Severe RSV disease is primarily a disease of young infants and children, with a peak occurrence at age 2-8 months. Reinfection with RSV occurs throughout life, with disease becoming more limited to the URT, as discussed above.

Clinical

History

Patients with respiratory syncytial virus (RSV) may present with the following symptoms:

• Fever (typically low-grade)
• Cough
• Tachypnea
• Cyanosis
• Retractions
• Wheezing
• Rales

Physical

Physical examination of the infant with RSV LRT reveals evidence of diffuse small airway disease. Up to 40% of children have an associated otitis media, which may be viral and/or bacterial. Additionally, assessment of the infant's hydration status (eg, skin turgor, capillary refill, mucous membranes) is an important part of the physical examination of the infant with bronchiolitis.

Causes

• In the community setting, a number of factors have been associated with increased risk of acquiring RSV disease, including the following:
  • Childcare attendance
  • Older siblings in preschool or school
  • Exposure to environmental pollutants (eg, cigarette smoke)
  • Multiple birth sets (especially triplets or greater)
  • Minimal breastfeeding
• In assessing an infant with RSV infection, several factors have been correlated with more severe disease and the need for hospitalization. Although infants in these groups (outlined below) are at increased risk for severe RSV disease compared to normal full-term infants based on percentage, many more children in the normal full-term group are admitted; thus, most admissions for RSV disease occur in otherwise normal infants. Family history of asthma and genetic factors also correlate with more severe RSV disease, although the exact relationship and mechanisms have not been elucidated.
  • Prematurity, especially birth at less than 35 weeks' gestation⁵
  • Age younger than 3 months at time of infection
  • Chronic lung disease
  • Congenital heart disease
  • Toxic appearance at time of presentation
  • Respiratory rate more than 70 per minute in room air
  • Atelectasis and/or pneumonitis on chest radiography
  • Oxygen less than 95% on room air

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