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    Bronchiolitis: The Old, The New, An Overview and Review
    (April 2005)


    Literally, bronchiolitis means inflammation of the bronchioles. Clinically, bronchiolitis refers to a viral infection of the lower airways in infants younger than 24 months old characterized by fever, cough, dyspnea, rhinorrhea and wheeze.

    Annually, it is estimated that 1-2% of all previously healthy children <1 year old are hospitalized for bronchiolitis[1]. The hospitalization rate is higher among “high risk” infants, who are identified as:

    • being born prematurely;
    • having chronic lung disease;
    • having congenital heart disease;
    • are male.


    Of previously healthy children who are hospitalized with bronchiolitis, it is estimated that:

    • 10 - 15% will require intensive care with about 50% of those children requiring ventilatory support secondary to respiratory failure[2].
    • <1% mortality of these children hospitalized due to bronchiolitis; while there is as much as a 3.5% mortality for high-risk infants hospitalized due to bronchiolitis[2].


    The evaluation and treatment of hospitalized children with bronchiolitis is mainly supportive and depends on the patient’s clinical picture. Since bronchiolitis is a clinical diagnosis, there are no mandatory laboratory studies. Rather, the lab studies are only supportive and may include:

    • viral cultures and/or direct fluorescent antibody tests;
    • chest radiographs; and
    • complete blood count and electrolytes.


    Although there is some controversy regarding the use of certain treatment options, the traditional treatment options are:

    Not Controversial

    • hydration and nutrition;

    • suctioning of secretions, especially prior to feeding;

    • oxygen for hypoxemia at rest;
    Controversial
    • bronchodilator treatment (racemic epinephrine or albuterol);

    • corticosteroids (inhaled vs. systemic);

    • heliox;

    • nebulized hypertonic saline
    There has been considerable research into each of the treatments in the controversial category. Unfortunately, the data from these studies do not provide a straightforward answer. There is support for both using and not using these treatments. The best guide for the proper use of these controversial treatments is monitoring clinical effect. In other words, make sure that the patient, in whom these treatments are used, is closely monitored both before and after receiving treatment. If there is little to no clinical benefit appreciated from the treatment, stop using it. In addition to Mandelberg’s and Patel’s articles, there is a nice review with good references by Steiner that discusses these controversial treatments[3-5].

    One of the questions that parents often pose is whether bronchiolitis causes asthma. Again, there has been a considerable amount of literature written on this relationship without a straightforward answer. However, it is known that bronchiolitis can cause a significant amount of wheezing following the initial illness. A recent study by Bisgaard et al. looked at preventing post-bronchiolitis wheezing in children whose bronchiolitis was caused by respiratory syncytial virus (RSV). They found that montelukast was a successful therapy [6].

    It is important to differentiate the term bronchiolitis from RSV bronchiolitis. In fact, the term bronchiolitis is often used (incorrectly) to infer an infection with RSV, but there are many other viral agents that cause bronchiolitis. These agents include “old” viruses: parainfluenza, influenza, adenovirus and rhinovirus, as well as the “new” virus human metapneumovirus (hMPV).

    hMPV is a relatively “new” virus that was discovered in the Netherlands by van den Hoogen et al. in 2001 [7]. Initially, researchers thought hMPV was a new virus, but then found that it has been circulating in the human population for the last 50-plus years. hMPV is a RNA virus closely related to avian pneumovirus. It is classified within the genus Metapneumovirus, subfamily Pneumovirinae. The only other genus in this Pneumovirinae subfamily is the one to which RSV belongs[8]. It is thought that hMPV can account for 5-12% of all lower respiratory tract illnesses in children[9].

    Since hMPV is closely related to RSV, it is not surprising to find that it causes the same clinical symptoms (fever, dyspnea, rhinorrhea, cough, etc), has a very similar season (October through May), and has the same high-risk population (premature, chronic lung disease, and complex congenital heart disease) that RSV does [8, 10]. Unfortunately, hMPV is hard to isolate because it requires special cell cultures. Quick clinical laboratory tests are currently being developed, but for now, real-time PCR is the only way to assay for it.

    As more about hMPV is being discovered, it is interesting to note that it is often found as a coinfection with other respiratory viruses. In addition to severe acute respiratory syndrome (SARS), hMPV is found as a coinfection with RSV. The importance of hMPV coinfection with RSV is not clearly defined, but there is some evidence that coinfection with these two viruses predispose a patient to having severe respiratory disease[8]. If this is true, the practice of cohorting non-RSV-bronchiolitis patients with RSV-bronchiolitis patients needs to be reviewed and quite possibly stopped.

    References:

    1. Tristram, D. and R. Welliver, Lower Respiratory Infections, in Principles and Practice of Pediatric Infectious Diseases, 2nd edition., S. Long, Editor. 2003, Elsevier Science: Philadelphia. p. 214.

    2. Navas, L., et al., Improved outcome of respiratory syncytial virus infection in a high-risk hospitalized population of Canadian children. Pediatric Investigators Collaborative Network on Infections in Canada. J Pediatr, 1992. 121(3): p. 348-54.

    3. Mandelberg, A., et al., Nebulized 3% hypertonic saline solution treatment in hospitalized infants with viral bronchiolitis. Chest, 2003. 123(2): p. 481-7.

    4. Patel, H., et al., A randomized, controlled trial of the effectiveness of nebulized therapy with epinephrine compared with albuterol and saline in infants hospitalized for acute viral bronchiolitis. J Pediatr, 2002. 141(6): p. 818-24.

    5. Steiner, R.W., Treating acute bronchiolitis associated with RSV. Am Fam Physician, 2004. 69(2): p. 325-30.

    6. Bisgaard, H., A randomized trial of montelukast in respiratory syncytial virus postbronchiolitis. Am J Respir Crit Care Med, 2003. 167(3): p. 379-83.

    7. van den Hoogen, B.G., et al., A newly discovered human pneumovirus isolated from young children with respiratory tract disease. Nat Med, 2001. 7(6): p. 719-24.

    8. van den Hoogen, B.G., D.M. Osterhaus, and R.A. Fouchier, Clinical impact and diagnosis of human metapneumovirus infection. Pediatr Infect Dis J, 2004. 23(1 Suppl): p. S25-32.

    9. Williams, J.V., et al., Human metapneumovirus and lower respiratory tract disease in otherwise healthy infants and children. N Engl J Med, 2004. 350(5): p. 443-50.

    10. Kahn, J.S., Human metapneumovirus, a newly emerging respiratory virus. Pediatr Infect Dis J, 2003. 22(10): p. 923-4.

    This information provided by Edward Fong, M.D., Pediatric Pulmonary & Cystic Fibrosis Center
    Tel: (510) 428-3305