The diagnosis is primarily clinical. Investigations are performed to rule out other causes of symptoms.
Patients typically present with cough, which may be productive, and symptoms suggestive of bronchial obstruction (such as intermittent wheeze or dyspnoea). However, the key point is that the cough and bronchial obstructive symptoms are acute and related to other signs of a respiratory infection, such as rhinorrhoea, sore throat, and low-grade fever. There is no universally accepted definition for acute bronchitis. Criteria suggested by MacFarlane state that the acute illness lasts for <21 days. However, the cough lasts for >2 weeks in 50% of patients and may last up to 4 weeks in 25% of patients.
It is important to enquire about symptoms of chronic respiratory conditions (such as asthma) or other lower respiratory tract infections, such as pneumonia (dyspnoea, cough, pleuritic chest pain, fever, rigours, malaise, and haemoptysis). Patients whose cough has progressed beyond 30 days also should be suspected of having a chronic pulmonary inflammatory disorder (sarcoidosis, Goodpasture's syndrome) or malignancy (lung cancer), especially if haemoptysis or other systemic symptoms such as weight loss are present.
Several medication or environmental exposures can also cause acute cough. These include the use of ACE inhibitors or occupational exposures to dusts or chemicals. In many of these cases, such as ACE inhibitor use, the cough is non-productive. In occupational exposures, symptoms are generally restricted to the cough, without any other systemic symptoms such as fever, headaches, or lethargy.
There is limited evidence for an association between household air pollution (from domestic solid fuel use) and the risk of acute lower respiratory infection.
The physical examination may reveal signs of upper respiratory tract infection, such as coryza, nasal congestion, and pharyngeal hyperaemia. There may also be evidence of bronchial obstruction (which can include prolonged expiratory phase) and wheezing, which may be brought out by forced expiration in the prone position, or rhonchi. The presence of rales on physical examination should prompt investigation for pneumonia or congestive heart failure (CHF).
Pulmonary function tests (PFT)
Pulmonary function testing is not recommended in patients with acute bronchitis. If done because underlying asthma is suspected, clinicians should be aware that patients with acute bronchitis will show mild to moderate bronchial obstruction that clears with resolution of their infection and should not be confused with asthma. If underlying asthma is suspected, PFTs should be delayed until the patient has fully recovered from their infection.
Laboratory studies are not needed in the diagnosis of acute bronchitis. In particular, examination of the sputum by either Gram stain or culture is not helpful. If other diagnoses are suspected (e.g., pneumonia), laboratory studies may be selected to confirm these.
In the UK, Public Health England recommend that C-reactive protein should be ordered if antibiotic therapy is being considered to help guide therapy.
Routine imaging is not indicated in patients with suspected acute bronchitis. In situations where other respiratory conditions may be present, such as pneumonia, CHF, or bronchiectasis, or in the presence of haemoptysis, appropriate imaging studies should be performed. However, these should be directed at ruling out other causes of cough rather than confirming acute bronchitis.
Procalcitonin is emerging as a promising biomarker for the diagnosis of bacterial infections as it tends to be higher in severe bacterial infections and low in viral infections. The US Food and Drug Administration has approved procalcitonin as a test for guiding antibiotic therapy in patients with acute respiratory tract infections. A Cochrane review of studies employing procalcitonin to differentiate between bacterial versus viral respiratory infections may indicate some value in reducing the use of antibiotics for this condition. Although most patients in the study had pneumonia, sepsis, or other potentially serious infections, the study did include a subset of patients who presented with acute bronchitis and had reductions in antibiotic use when this test was used. Further research is required.
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