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Bronchiolitis – It Is Time for a Unique Definition
Fabio Midulla and Raffaella Nenna
Department of Paediatrics and Infantile Neuropsychiatry, ‘Sapienza’ University of Rome, Rome, Italy
Abstract Bronchiolitis is the most common lower respiratory tract infections in infants. It is time to reach a unique clinical definition,
encompassing the acute onset of respiratory distress with cough, tachypnoea, retraction and diffuse crackles on auscultation in
infants aged less than 12 months.
Keywords Bronchiolitis, definition, age, respiratory syncytial virus
Disclosure: Fabio Midulla and Raffaella Nenna have nothing to declare in relation to this article. No funding was received for the publication of this paper. This article is a
short opinion piece and has not been submitted to external peer reviewers.
Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation
and reproduction provided the original author(s) and source are given appropriate credit.
Received: 20 January 2016 Published Online: 3 May 2016 Citation: European Respiratory & Pulmonary Diseases, 2016;2(1):12–3
Correspondence: Fabio Midulla, Department of Paediatrics, ‘Sapienza’ University of Rome,V le Regina Elena 324, 00161, Rome, Italy. E: [email protected]
Acute bronchiolitis is the most common lower respiratory tract infection
in infants less than 12 months of age, and it is the leading cause of
hospitalisation in this age group, particularly in infants younger than
six months. It is mainly caused by respiratory syncytial virus (RSV) and
shows a seasonal pattern, with peak incidence occurring during winter,
but other respiratory viruses can often be involved. 1 Particularly, infants
with RSV bronchiolitis are younger, have been breastfed for a shorter
time and have a more severe form of bronchiolitis with prevalent chest
X-ray findings of diffuse air trapping, whereas, human Rhinovirus (hRV),
the second most frequent virus involved, seems to cause a milder
form of bronchiolitis and affecting infants with a higher eosinophils
count and, possibly, with an atopic predisposition. 1 Each year 150
million new cases of bronchiolitis are reported worldwide with an
increasing trend in medical visits and total hospitalisations along with
the diagnosis of bronchiolitis.
Despite the fact that bronchiolitis is an ‘old’ disease, several aspects are
still debated. First, a clear definition of this entity is still lacking. According
to the European definition, bronchiolitis is a clinical diagnosis requiring
epidemiological data, such as the epidemic period (December to March),
the age of infants and the specific clinical appearance (signs of an upper
respiratory infection: runny nose, fever, chough, followed by respiratory
distress with diffuse crackles on auscultation). 2 On the contrary, the
American Pediatric Academy defines bronchiolitis as the first episode of
acute viral wheeze occurring in infants less than two years old. It is evident
that this definition likely overlaps the early presentation of wheezing or
bronchial hyper-responsiveness. 3 To exclude infants with virus-associated
episodes of wheezing, we should consider bronchiolitis only in infants
younger than 12 months presenting with their first episode of lower
respiratory infection, who had diffuse crackles on auscultation. 4 Wheezing
is a high-pitched, musical, adventitious lung sound produced by turbulent
airflow through a narrowed airway, whereas crackles are caused by the
‘popping open’ of small airways and alveoli collapsed by fluid, thus possibly
reflecting two different entities affecting two different lung structures.
12 Second, it is a self-limiting disease and it should be managed only with
supportive care. Reduced feeding is common and very young infants
may present with apnoeic episodes, thus leading to hospitalisation,
which is required by 2–3% of infants affected. 5 Some patients,
particularly when risk factors are present, can manifest a severe
disease and the admission to the intensive care unit may be required.
Few predisposing factors may explain the clinical worsening, leading to
paediatric intensive care unit admission for ventilatory support. Young
age (under one month), possibly due to the small size of the airways, and
RSV carriage are the most important demographic factors associated
with severe respiratory distress that is uncommon in previously healthy
term infants and often develops soon after disease onset.
Furthermore, the conflict that exists in the definition creates many
problems, especially in the interpretation of results of clinical trials and
the relationship between bronchiolitis and wheezing and asthma. A single
definition of bronchiolitis will allow an analysis of the homogeneous
disease pathogenesis and the possible role of new therapeutic
strategies. The exclusive use of supportive treatments (nasal washing, O 2
and hydration) is restricted for pure bronchiolitis infants. In fact, bubbly
nasopharyngeal secretions, by obstructing the nostrils may cause
transient decreases in SpO 2 in infants that are obligate nasal breathers.
On the other hand, several medical therapies might be useful in wheezing
children 12–24 months old. For example, the use of bronchodilators, as
well as of corticosteroids, is no longer recommended for bronchiolitis
infants, but may play a role in wheezing children. Overlapping these
two diagnoses could result in erroneous management of children with
respiratory failure. Nowadays, there is a huge variability in the clinical
management of this disease around the world, including widespread use
of unnecessary tests and ineffective therapies.
Moreover, long-standing evidence underlines the role of bronchiolitis
in the occurrence of subsequent wheezing and asthma, especially in
infants with hRV infection and a high eosinophils count during the
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