Acute Bronchitis

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Clinical Description

Acute bronchitis is an inflammatory condition of the tracheobronchial tree usually associated with a generalized respiratory infection. Cough begins early in the course of the illness and is the most prominent feature of the condition. An initially dry cough may later result in sputum production which characteristically changes from clear to discolored in the later stages of the illness. The cough may last for a significant time.

Although the duration of the condition is variable, one study showed that 50% of patients had a cough for more than 3 wk and 25% had a cough for more than 4 wk (87).

Patients with acute bronchitis usually have a viral respiratory infection with transient inflammatory changes that produce sputum and symptoms of airway obstruction. Acute bronchitis is essentially a diagnosis of exclusion. The history should include information on cigarette use, exposure to environmental toxins, as well as medication history (e.g., use of angiotensin converting enzyme inhibitors). The chronicity of the cough should be established to distinguish acute bronchitis from chronic bronchitis, as they have different treatments.

Both acute bronchitis and pneumonia can present with fever, constitutional symptoms, and a productive cough. Although patients with pneumonia often have rales, this finding is neither sensitive nor specific for the illness. When pneumonia is suspected on the basis of a presence of a high fever, constitutional symptoms, severe dyspnea, and certain physical findings or risk factors, a chest radiograph should be obtained to confirm the diagnosis.

Asthma and allergic bronchospastic disorders can mimic the productive cough of acute bronchitis. When obstructive symptoms are not obvious, mild asthma may be diagnosed as acute bronchitis. Further, because respiratory infections can trigger bron-chospasm in asthma, patients with asthma that occurs only in the presence of respiratory infections resemble patients with acute bronchitis.

Asthma should be considered in patients with repetitive episodes of acute bronchitis. Patients who repeatedly present with cough and wheezing can be given full spirometric testing with bronchodilation or provocative testing with a methacholine challenge test to help differentiate asthma from recurrent bronchitis.

Finally, nonpulmonary causes of cough should enter the differential diagnosis. In older patients, congestive heart failure may cause cough, shortness of breath and wheezing. Reflux esophagitis with chronic aspiration can cause bronchial inflammation with cough and wheezing. Bronchogenic tumors may produce a cough and obstructive symptoms.

Epidemiology

Acute bronchitis in the otherwise healthy adult is one of the most common medical problems encountered in primary care (5). The prevalence of acute bronchitis peaks in the winter and is much less common in the summer.

Etiology

Viral infection is considered the primary cause of most episodes of acute bronchitis. A wide variety of viruses have been shown as causes of acute bronchitis including influenza, rhinovirus, adenovirus, coronavirus, parainfluenza, and respiratory syncytial virus (88). Nonviral pathogens including Mycoplasma pneumoniae and Chlamydia pneumoniae (TWAR) have also been identified as causes (89,90).

The etiologic role of bacteria such as Haemophilus influenzae and Streptococcus pneumoniae in acute bronchitis is unclear because these bacteria are common upper respiratory tract flora. Sputum cultures for acute bronchitis are therefore difficult to evaluate, as it is unclear whether the sputum has been contaminated by pathogens in the nasopharynx.

Treatment

Antibiotic treatment for acute bronchitis is quite common, with evidence indicating that 60-75% of adults visiting a physician for acute bronchitis receiving an antibiotic (21,91). Clinical trials of the effectiveness of antibiotics in treating acute bronchitis have produced mixed results. One reason for the lack of consensus is that in each of the nine trials different antibiotics were used and different outcomes were obtained. In an effort to quantitatively review the data, two different meta-analyses were recently conducted (92,93). In the Fahey et al. meta-analysis, resolution of cough was not affected by antibiotic treatment and neither was clinical improvement at reexamination. Importantly, the side effects of antibiotics were more common in the antibiotic groups compared to placebo. The Smucny et al. meta-analysis concluded that antibiotics may be modestly effective for a minority of patients with acute bronchitis although it is unclear which subgroups might benefit. The conclusion of both meta-analyses was that the benefits or antibiotics are marginal and are not useful for the general group of patients with acute bronchitis.

Recent data from clinical trials suggest that bronchodilators may provide effective symptomatic relief to patients with acute bronchitis (94,95). Treatment with bron-chodilators demonstrated significant relief of symptoms including faster resolution of cough, as well as return to work. One study evaluated the effect of albuterol in a population of patients with undifferentiated cough and found no beneficial effect (96). Because a variety of conditions present with cough there may have been some misclas-sification in generalizing this to acute bronchitis.

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