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2. Etiology

The most common cause of bronchiolitis is viral pathogen, such as respiratory

syncytial virus, rhinovirus, adenovirus, influenza virus, and parainfluenza virus. RSV

is the most commonly isolated pathogen in 75% of patients under 2 years of age.

Other causes are Mycoplasma pneumonia, however there is still no evidence of

bacterial infection in bronchiolitis. Most of bronchiolitis cases are self-limiting,

which make virological and bacterial testing needed to confirm the pathogen affecting

the infants is hardly needed. In addition, even with different types of pathogen as the

etiology, there will be no difference in treatment. (Medscape, JAMA)

3. Epidemiology

Bronchiolitis is the most common lower respiratory tract infection in infants.

The infection happens mostly in children under 2 years of age with the highest

incidence in 3-6 months of age. Children less than 6 months old usually have the

more severe disease with higher mortality and morbidity rate.(IDAI) The infection is

seasonal and the highest prevalence is in winter or in colder weather. Based on

Scottish morbidity recording for the years 2001 to 2003 a mean of 1976 children per

year (aged up to 12 months) were admitted to hospital with bronchiolitis as the

principal diagnosis. According to Koehoorn et al, males are 1.38 times more

susceptible of developing bronchiolitis than females. The study which were

performed in British Columbia, also found an increased incidence of bronchiolitis in

children born to young mothers, no initiation of breastfeeding in the hospital, infants

with low birth weight, and infants living with older siblings. (Koehoorn)

4. Diagnostic Investigation

Bronchiolitis should be diagnosed only by history and physical examination.

However, further diagnostic study could be performed when diagnostic uncertainty

exists or to aid decision making regarding subsequent management. These

investigations may include blood gases analysis, oxygen saturation recording, chest

x-ray, and viral or bacterial testing, and antibody titer measurement in acute and

convalescence phase. (NHS_SIGN)

Pulse oxymetry should be performed especially in severe cases. According to,

lower the oxygen saturation predicts more severe disease and longer length of stay.

Oxygen saturation 92% requires inpatient care, while oxygen saturation >90% may

be considered for discharged. Aterial blood gases analysis is not indicated in

bronchiolitis patient except severe cases. Knowledge of arterialized carbon dioxide

values may guide

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Both oxygen saturation measurement and arterial blood analysis could be used

for determination of severity of illness. Indication of oxygen therapy and the

concentration could be determined by the degree of hypercarbia or hypoxemia

(PaCO2).

Many studies have tried to determine the relationship of the use of chest x-ray

in diagnosing and treating patients with bronchiolitis. Shaw et al found a connection

of abnormal chest x-ray outcomes with severity of disease. In contrary, data from

Dawson et al demonstrated no correlation between chest x-ray film findings and

baseline disease severity as measured by a clinical severity scoring system. Study by

Swingler concluded that children receiving chest x-ray examination were more likely

to be diagnosed as having pneumonia and treated with antibiotics; children who did

not receive chest x-ray examination were more likely to be diagnosed as having

brochiolitis. (JAMA) According to Scottish Intercollegiate Guidelines Network, chest

x-ray should only be performed in selected cases as it rarely affects the course of

treatment. It also can be used in infants with diagnostic uncertainty or an atypical

disease course. (SIGN)