The most common differential diagnosis will be prolonged cough following infection. It is important to distinguish possible ongoing protracted bacterial bronchitis from persistent cough following a viral infection or several successive viral infections with wet cough (acute bronchitis) (2, 3, 10, 20).
Other causes that should be considered are foreign bodies in the respiratory tract and cough due to adenotonsillar hypertrophy. Rare, but important differential diagnoses are cystic fibrosis, bronchiectasis, primary ciliary dyskinesia, pulmonary aspiration and immunodeficiency (20).
A tidal volume curve that shows obstruction during exhalation may indicate airway malacia as the cause of the symptoms, and in the event of obstruction that is reversible with salbutamol, asthma should be considered (1, 9). Asthma may be considered in cases of chronic wet cough, but is seldom a cause, and should not be diagnosed in cases of chronic wet cough alone. The cough accompanying asthma will most frequently be dry, and the symptoms dominated by recurrent and reversible episodes of bronchopulmonary obstruction. Protracted bacterial bronchitis may nevertheless be a complication of asthma, or occur concurrently with asthma, when there will usually still be episodes of obstruction in addition to chronic cough (1).
When protracted bacterial bronchitis is suspected and antibiotics are ineffective, the child should be assessed for other possible causes (19), and other severe pulmonary disease must also be considered if Pseudomonas aeruginosa develops in the bacterial culture. Further assessment is also recommended in the event of a second recurrence of symptoms (1, 2).
Relevant investigations will then be a sweat test (cystic fibrosis), nasal nitric oxide measurement (primary ciliary dyskinesia), CT thorax (bronchiectasis) and immunological assessment, initially with measurement of immunoglobulins and vaccine antibody levels (2, 21). Bronchoscopy may also be relevant when the above tests have not identified any cause (2).