Excerpt from Respiratory Syncytial Virus Infection

Synonyms, Key Words, and Related Terms: respiratory syncytial virus infection, RSV, bronchiolitis, viral pneumonia, lower respiratory tract infection, LRT infection, upper respiratory tract infection, URT infection, chimpanzee coryza agent, Rs virus

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Background: Respiratory syncytial virus (RSV) infection, which manifests primarily as bronchiolitis 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.

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:

In the US: 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.

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

Mortality/Morbidity: Even in children hospitalized with R .....