Viral Bronchiolitis

Posted by • January 8th, 2016

1-5-2016 11-58-44 AMFew diseases have a greater effect on the health of young children than viral lower respiratory tract illness. Approximately 800,000 children in the United States, or approximately 20% of the annual birth cohort, require outpatient medical attention during the first year of life because of illness caused by respiratory syncytial virus (RSV). This review article on viral bronchiolitis in young children considers the viruses involved, the current understanding of pathogenesis, host genetic factors and the environment, and the role of season, race, and sex on attack rates and subsequent episodes of wheezing.

Clinical Pearl

• Is the course of viral bronchiolitis or the response to treatment influenced by the specific viral etiology?

RSV accounts for 50 to 80% of all hospitalizations for bronchiolitis during seasonal epidemics in North America. Although the clinical features of bronchiolitis due to different viruses are generally indistinguishable, some differences in the severity of disease have been reported. For example, it has been observed that rhinovirus-associated bronchiolitis may result in a shorter length of hospitalization than bronchiolitis that is attributable to RSV. Differences in the response to medical intervention have not been identified consistently among children with bronchiolitis caused by different viruses.

Table 1. Viruses Detected in Nasopharyngeal Secretions

Clinical Pearl

• What is hypothesized to contribute to severe disease in infants with a first episode of RSV bronchiolitis?

The immune response elicited by RSV may be both protective and pathogenic, and there appear to be functional differences between an initial infection in a seronegative infant and reinfection in an older child or adult. At least in infants who have not had a previous infection, overwhelming RSV disease appears to be related to the lack of an adaptive cytotoxic T-cell response in the host; the result is dependence on the less effective innate immune response for the termination of viral replication. The fact that a more effective, adaptive cytotoxic T-cell response does not develop in such infants is supported by reports of a direct correlation between RSV load, as measured in nasopharyngeal aspirates obtained from children who have been hospitalized with bronchiolitis, and more severe disease, defined as a higher risk of apnea, a longer hospital stay, and a greater need for intensive care. However, not all reports are consistent with an association between a high viral load in respiratory secretions and greater severity of disease. A reasonable deduction is that direct cytotoxic injury induced by the virus and a robust host inflammatory response both contribute to the pathogenesis of RSV bronchiolitis, although the relative contribution of each remains uncertain.

Figure 1. Pathogenesis of Bronchiolitis Due to Respiratory Syncytial Virus (RSV).

Morning Report Questions

Q: What are some of the risk factors for the development of severe bronchiolitis?

A: Most infants who are hospitalized with RSV bronchiolitis were born at full term with no known risk factors. Chronologic age is the single most important predictor of the likelihood of severe bronchiolitis, given the observation that approximately two thirds of hospitalizations of infants with RSV infection occur in the first 5 months of life. Hospitalization rates that are attributable to RSV are highest between 30 and 90 days after birth, a period that corresponds to the declining concentration of transplacentally acquired maternal immunoglobulin. Because most maternal immunoglobulin transfer occurs in the third trimester, preterm infants may miss the period of greatest IgG transfer; this fact partly explains the higher risk of disease among preterm infants. Maternal RSV antibody concentrations vary seasonally, with significantly higher serum concentrations being observed later in the RSV season than earlier in the season. Lower serum concentrations of maternal RSV antibody (resulting from waning maternal immunity from infection during the previous season) may account for the more severe disease that is observed among infants born early in the RSV season, as compared with those who are born later.

Q: How is viral bronchiolitis managed, and is any type of prophylaxis available? 

A: No available treatment shortens the course of bronchiolitis or hastens the resolution of symptoms. Therapy is supportive, and the vast majority of children with bronchiolitis do well regardless of how it is managed. The intensity of therapy among hospitalized children has been shown to have little relationship to the severity of illness. The evidence-based guidelines of the American Academy of Pediatrics  emphasize that a diagnosis of bronchiolitis should be based on the history and physical examination and that radiographic and laboratory studies should not be obtained routinely. Short-acting β2-agonists, epinephrine, and systemic glucocorticoids are not recommended for the treatment of children with bronchiolitis. Clinicians may elect not to administer supplemental oxygen when oxyhemoglobin saturation exceeds 90%. Palivizumab, a humanized mouse IgG1 monoclonal antibody directed against a conserved epitope on the surface fusion protein of RSV, was licensed by the Food and Drug Administration in June 1998 for monthly prophylaxis for infants at high risk for RSV infection. Recommendations for more restrictive use of passive immunoprophylaxis have evolved since palivizumab was licensed as additional information has become available regarding the epidemiology of RSV and the limited benefit of prophylaxis. Several approaches to vaccine development are being investigated. Until safe and effective vaccines are available, reduction of the burden of disease due to bronchiolitis will focus on education about the importance of decreasing exposure to and transmission of respiratory viruses.

Table 2. American Academy of Pediatrics Guidance for Diagnosis and Management of Bronchiolitis.

Table 3. American Academy of Pediatrics Guidance for Palivizumab Immunoprophylaxis.

3 Responses to “Viral Bronchiolitis”

  1. Kannan says:

    I t is a useful article in the context of final push for lowering child mortality in developing

    countries also. The sustainable Development Goals by 2025 will require investments to

    control RS bronchiolitis by innovative strategies through a public health and Primary care

    approach.

  2. Dorothy E Clay says:

    Most appreciated to read this information. T Y Dr. Steven Corleone.

  3. luis ponce says:

    Great article. thanks.