Acute tracheobronchitis is acute inflammation of the tracheal and bronchial mucosa caused by biological, physical, chemical, or allergic factors, affecting the large airways or lobar/segmental bronchi. It is usually self-limiting and resolves within 1-3 weeks. The condition is sporadic, affecting approximately 5% of the population annually, without epidemic tendencies. Older and frail individuals are more susceptible. The primary symptoms are cough and expectoration, often occurring during cold seasons or sudden weather changes. It may also result from unresolved acute upper respiratory tract infections. A clinical diagnosis can generally be established based on cough symptoms after ruling out pneumonia.
Etiology and Pathogenesis
Microorganisms
The pathogens are similar to those causing upper respiratory tract infections. Viruses commonly involved include adenovirus, influenza viruses (types A and B), coronaviruses, rhinoviruses, herpes simplex virus, respiratory syncytial virus, and parainfluenza viruses. Bacteria such as Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis are frequently implicated. In recent years, Chlamydia and Mycoplasma infections have been increasingly recognized. Secondary bacterial infections following viral infections are also common. These pathogens can cause inflammation in the large airways and may extend to the small airways or alveoli, leading to symptoms such as cough, wheezing, and tachypnea.
Physical and Chemical Factors
Inhalation of cold air, dust, or irritant gases or fumes (e.g., sulfur dioxide, nitrogen dioxide, ammonia, chlorine gas) can stimulate the tracheobronchial mucosa, causing acute injury and inflammatory responses.
Allergic Reactions
Allergic reactions to inhaled allergens such as pollen, organic dust, fungal spores, animal dander, and excreta can trigger acute tracheobronchial inflammation. Similarly, hypersensitivity to bacterial proteins or larval migration of hookworms and ascaris in the lungs may also lead to acute inflammation.
Pathology
The tracheal and bronchial mucosa exhibit congestion and edema, with infiltration of lymphocytes and neutrophils. Damage to and shedding of ciliated epithelial cells, along with hypertrophy and hyperplasia of mucus glands, may be observed. In cases of bacterial infection, secretions may become purulent.
Clinical Manifestations
Symptoms
The onset is usually acute, with mild systemic symptoms and occasional fever. Initial symptoms include dry cough or scanty mucus expectoration, which later progresses to increased expectoration and worsening cough. Blood-streaked sputum may occur occasionally. Cough and expectoration may persist for 2-3 weeks. If unresolved, acute tracheobronchitis may progress to chronic bronchitis. Chronic bronchitis is diagnosed when patients experience recurrent cough and expectoration for at least three months annually for two consecutive years. Acute bronchitis with bronchospasm may cause varying degrees of chest tightness and dyspnea.
Signs
Physical examination may reveal no significant abnormalities, or scattered dry and moist crackles may be heard in both lungs. These sounds are not fixed in location and may decrease or disappear after coughing.
Laboratory and Other Auxiliary Examinations
Peripheral blood leukocyte counts are usually normal, but bacterial infections may show elevated total leukocyte counts and a higher percentage of neutrophils. Erythrocyte sedimentation rate (ESR) may be increased.
Sputum cultures may identify pathogenic bacteria.
Chest X-rays typically show enhanced pulmonary markings, with no abnormalities in some cases.
Diagnosis and Differential Diagnosis
A clinical diagnosis can be established based on the patient's history, symptoms of cough and expectoration, scattered dry and moist crackles in both lungs, and findings from blood tests and chest X-rays. Viral and bacterial tests can assist with etiological diagnosis. Differential diagnosis is necessary to distinguish acute tracheobronchitis from the following conditions:
Influenza
Influenza has a sudden onset, higher fever, and more pronounced systemic symptoms (e.g., body aches, headache, fatigue) compared to relatively mild respiratory symptoms. Epidemiological history, viral isolation from secretions, and serological tests can aid in differentiation.
Acute Upper Respiratory Tract Infection
Symptoms predominantly involve the nasopharynx, with mild cough and mild to no expectoration. The course typically resolves within a week, and lung examination is normal. Chest X-rays are also unremarkable.
Bronchiolitis
It is characterized by cough, chest tightness, and wheezing, with characteristic findings on chest CT or X-rays.
Other Conditions
Other pulmonary diseases such as bronchopneumonia, tuberculosis, lung cancer, lung abscess, measles, and pertussis may present with similar symptoms of cough and expectoration. Thorough examination is required for differentiation.
Treatment
Symptomatic Treatment
For dry cough or cough with scanty sputum, antitussives such as compound methoxyphenamine or pentoxyverine can be used.
For cough with difficult-to-expectorate sputum, mucolytics such as ambroxol, myrtol, or cineole may be prescribed, along with nebulized therapy.
Bronchodilators such as theophylline, β2-adrenergic agonists, or anticholinergic agents can be used for bronchospasm.
Antipyretic and anti-inflammatory drugs can be used to manage fever.
Antibiotic Therapy
Antibiotics are only recommended when there is evidence of bacterial infection. Persistent cough lasting more than 10 days increases the likelihood of bacterial, Mycoplasma, or Chlamydia pneumoniae infection. First-line treatments include newer macrolides, cephalosporins, or fluoroquinolones. The CDC recommends azithromycin for 5 days, clarithromycin for 7 days, or erythromycin for 14 days. Most patients can take oral antibiotics, but intramuscular or intravenous administration may be necessary for severe cases. Antibiotic selection should ideally be guided by pathogen culture results.
General Management
Patients should rest, avoid overexertion, and refrain from smoking or exposure to smoke.
Prognosis
Most patients have a good prognosis. However, in frail individuals, the condition may persist, with symptoms lasting more than one month in 20% of cases, requiring increased attention.
Prevention
Prevention strategies:
- Strengthen physical fitness, avoid overexertion, and prevent colds.
- Improve living and sanitary conditions, and avoid exposure to polluted air and allergens.