Bronchiolitis natural history

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:  Alonso Alvarado, M.D. [2]

## Overview

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If left untreated, bronchiolitis may progress to develop mild upper respiratory symptoms including, cough, rhinorrhea and low grade fever during the first 1-2 days. During third to seventh days of infection, patients develop shortness of breath, wheezing, persistent prominent cough, tachypnea, chest wall retraction, and nasal flaring. Symptoms gradually disappear within the next 2 weeks. Complications are usually observed in patients younger than 2 months of age, premature infants, and patients with other medical conditions (including congenital heart disease, chronic pulmonary disease, and immunodeficiencies). Severity scores can be used to estimate the prognosis.

## Natural History

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* Patients usually develop symptoms after one week of initial contact with a symptomatic patient.
* In the first 2-3 days, patients with bronchiolitis present with mild upper respiratory symptoms (cough, rhinorrhea, and low grade fever).
* The acute phase (shortness of breath, wheezing, persistent prominent cough, tachypnea, chest wall retraction, and nasal flaring) usually develops between the third and seventh days.
* Symptoms gradually disappear within the next 2 weeks (the cough may take longer to resolve).
* Bronchiolitis is usually a self-limited infection that should be eliminated in two weeks after infection in immunocompetent patients. However, dissemination of the virus in immunocompromised patients could remain for several months after initial infection.[1]

## Complications

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Complications are usually observed in patients younger than 2 months, premature infants and patients with various comorbidities (congenital heart disease, chronic pulmonary disease, and immunodeficiencies). Common complications of bronchiolitis include the following:

* Apnea:[1]
* Apnea may appear as the presenting manifestation; however, it may be the consequence of previous mild respiratory infection.
* More common in children under 2 months of age and premature infants.
* Observed in 3% to 25% of patients.
* Aspiration pneumonia
* Recurrent wheezing episodes:
* Observed in 30%-50% of hospitalized patients with bronchiolitis.
* Episodes usually disappear before adolescence.
* Associated bacterial infections:
* The most common bacterial infections complicating bronchiolitis are urinary tract infections (UTI) and acute otitis media (AOM).
* Bacterial co-infections may appear in up to 7 % of patients with bronchiolitis.

## Prognosis

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The prognosis of bronchiolitis is generally good, as most children show gradual symptomatic improvement within 2 weeks of symptom onset. Albeit the good prognosis, the rate of hospitalization is high (71 per 1000 infants for 2003) and has increased during the last two decades. The mortality rate of bronchiolitis is very low (2 deaths per 100,000 live births in the U.S. and 1.82 per 100,000 live births in the UK).[2]

Clinical scoring systems such as the following may help predict the prognosis:

* Bronchiolitis severity score (BSS)[3]
* Court's scale[4]
* Respiratory distress assessment instrument (RDAI)[5]
* Respiratory distress observation scale (RDOS)[6]
* Tal and modified-Tal scoring systems[7]

## References

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1. ↑ 1.0 1.1 Wright M, Mullett CJ, Piedimonte G (2008). "Pharmacological management of acute bronchiolitis". Ther Clin Risk Manag. 4 (5): 895–903. PMC 2621418. PMID 19209271.CS1 maint: Multiple names: authors list (link) CS1 maint: PMC format (link)
2. ↑ Smyth RL, Openshaw PJ (2006). "Bronchiolitis". Lancet. 368 (9532): 312–22. doi:10.1016/S0140-6736(06)69077-6. PMID 16860701.
3. ↑ Wang EE, Milner RA, Navas L, Maj H (1992). "Observer agreement for respiratory signs and oximetry in infants hospitalized with lower respiratory infections". Am Rev Respir Dis. 145 (1): 106–9. doi:10.1164/ajrccm/145.1.106. PMID 1731571.CS1 maint: Multiple names: authors list (link)
4. ↑ Court SD (1973). "The definition of acute respiratory illnesses in children". Postgrad Med J. 49 (577): 771–6. PMC 2495839. PMID 4806395.CS1 maint: PMC format (link)
5. ↑ Lowell DI, Lister G, Von Koss H, McCarthy P (1987). "Wheezing in infants: the response to epinephrine". Pediatrics. 79 (6): 939–45. PMID 3295741.CS1 maint: Multiple names: authors list (link)
6. ↑ Campbell ML (2008). "Psychometric testing of a respiratory distress observation scale". J Palliat Med. 11 (1): 44–50. doi:10.1089/jpm.2007.0090. PMID 18370892.
7. ↑ McCallum GB, Morris PS, Wilson CC, Versteegh LA, Ward LM, Chatfield MD; et al. (2013). "Severity scoring systems: are they internally valid, reliable and predictive of oxygen use in children with acute bronchiolitis?". Pediatr Pulmonol. 48 (8): 797–803. doi:10.1002/ppul.22627. PMID 22949369.CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link)

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