Lower respiratory tract infections are an important cause of morbidity and mortality worldwide in children and in adults. Community-acquired pneumonia, for example, is the most deadly infectious disease in the United States. This chapter takes an anatomic approach to lower respiratory tract infections, moving from the large bronchi (bronchitis) down to the very small bronchioles (bronchiolitis) and then into the alveoli where pneumonia occurs.
Bronchitis is an inflammation of the bronchi typically caused by viruses. Acute bronchitis must be distinguished from chronic bronchitis in which patients have a cough for more than 3 months. The information in this chapter refers to acute bronchitis.
The coughing so characteristic of bronchitis is an attempt to clear the mucus produced by the inflammatory response to viral infection. Bronchitis occurs more often in the winter months than in the summer. Smoking predisposes to bronchitis (and pneumonia) by damaging the cilia in the bronchi, leading to an inability to clear mucus from the respiratory tract.
Cough is the most prominent symptom of bronchitis. Initially, bronchitis presents with the symptoms of an upper respiratory infection, namely, nasal congestion, scratchy sore throat, and perhaps a low-grade fever. Physical examination typically reveals expiratory wheezes. However, if cough persists for more than 5 days and pneumonia has been ruled out, acute bronchitis should be suspected. Bronchitis is self-limited and usually resolves in 1 to 2 weeks. However, cough may persist for several more weeks due to airway hyperreactivity.
Respiratory viruses are the most common pathogens (influenza A and B, parainfluenza virus, coronavirus, rhinovirus, respiratory syncytial virus [RSV], and human metapneumovirus). Bacterial pathogens do not play a significant role in acute bronchitis. Acute exacerbations of chronic bronchitis may be caused by Streptococcus pneumoniae or Haemophilus influenzae.
The diagnosis is primarily made clinically. Cough, with or without sputum production, which may persist for more than 5 days, is the typical presentation. Patients are usually afebrile but may have a low-grade fever. Sputum cultures are typically not done. In patients with chronic cardiorespiratory disease, a rapid antigen test for influenza virus may be useful because oseltamivir (Tamiflu) can shorten the duration and intensity of symptoms.
Because treatment of both upper respiratory infections and acute bronchitis is largely supportive, these distinctions may have less clinical significance. What may be more important clinically is to distinguish acute bronchitis (usually viral) from pneumonia (mainly bacterial; see section on Pneumonia), which does require antimicrobial therapy. A chest radiograph may be performed to determine whether pneumonia is present.
Treatment involves patient education and symptom relief with agents such as over-the-counter cough medications, nonsteroidal ...