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Lower Respiratory Tract Infections


Acute bronchiolitis usually is caused by viruses with a specific trophism for the bronchiolar epithelium. It is characterized by inflammatory obstruction of small airways, with submucosal cellular infiltration with mononuclear cells, epithelial necrosis, mucous plugging, and airway narrowing leading to atelectasis. In most situations, recovery is complete, but if the insult is severe, necrosis can lead to fibrosis and bronchiolitis obliterans.

The small airways of the infant are responsible for most of the total airway resistance, and airflow can be critically diminished by minimal inflammatory changes of the bronchioles.

Bronchiolitis progresses over several days. Nasal discharge and cough begin 4-6 days after exposure. Apnea can be a sudden, early manifestation of disease, especially in formerly premature infants with a previous history of apnea.

Bronchiolitis occurs primarily in infants less than one year of age, with the peak incidence between 2 and 6 months of age. Wheezing occurs in 10-20% of infected children, and 1% of children less than one year of age require hospitalization.

Respiratory syncytial virus, bronchitis cold flu is the leading cause of bronchiolitis in infancy, with parainfluenza type 3 the next most common cause. Other viruses are less commonly seen. During the winter months, RSV is confirmed to be the cause in 80-100% of cases. RSV syncytial virus Parainfluenza virus 3.

The differential diagnosis also includes noninfectious causes: Airway Hypersensitivity to Environmental Stimuli, anatomic abnormalities, cardiac disease with pulmonary edema, lymphedema, cystic fibrosis, foreign body aspiration, or aspiration pneumonia.

The diagnosis.