Acute
Acute bronchitis is characterized by acute inflammation of the tracheobronchial tree. This condition may be part of, or preceded by, an upper respiratory tract infection such as influenza (the “flu”) or the common cold. Most infections occur during the winter when acute respiratory tract infections are common.
The pathogenesis of acute bronchitis has no specific documented etiology but appears to be a mixture of viral cytopathic events and a response by the host immune system. Regardless of the cause, the protective functions of the bronchial epithelium are disturbed and excessive fluid accumulates in the bronchi. Depending on the etiology, destruction of the bronchial epithelium may be either extensive (e.g., influenza virus) or minimal (e.g., rhinovirus colds).
Clinically, bronchitis is characterized by cough, variable fever, and sputum production. Sputum (pus from the lungs) is often clear at the onset but may become purulent as the illness persists. Bronchitis may manifest as croup (a clinical condition marked by a barking cough or hoarseness).
The value of microbiologic studies to determine the cause of acute bronchitis in otherwise healthy individuals has not been established. Acute bronchitis is caused by viral agents, such as influenza and respiratory syncytial virus (RSV). The bacterium Bordetella pertussis is often associated with bronchitis in infants and preschool children (Table 1). The best specimen for diagnosis of pertussis is a deep nasopharyngeal specimen collected with a calcium alginate swab.
Table1. Major Causes of Acute Bronchitis
Chronic versus Acute
Chronic bronchitis is a common condition affecting about 10% to 25% of adults. This disease is defined by clinical symptoms in which excessive mucus production leads to coughing up sputum on most days during at least 3 consecutive months for more than 2 successive years.
Cigarette smoking, infection, and inhalation of dust or fumes are important contributing factors. Acute bronchitis is not related to long-term etiologies causing damage to the lungs, but is typically a result of an infectious process.
Patients with chronic bronchitis can suffer from acute flare-ups of infection, but determination of the cause of the infection is difficult. Potentially pathogenic bacteria, such as nonencapsulated strains of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis, are frequently cultured from the bronchi of these patients. Because of chronic colonization, it is difficult to incriminate one of these organisms as the specific cause of an acute infection in patients with chronic bronchitis. Although the role of bacteria in acute infections in these patients is questionable, viruses are frequent causes.
