Differential Diagnosis for Persistent Dry Cough

Key Temporal Classification

At three months post-viral bronchitis, the patient's persistent dry cough has transitioned from subacute to chronic cough, and the American College of Chest Physicians (ACCP) guidelines recommend systematically evaluating for upper airway cough syndrome, asthma, gastroesophageal reflux disease, and nonasthmatic eosinophilic bronchitis 1, 2
This is now chronic cough (>8 weeks duration), not postinfectious cough, which by definition resolves within 8 weeks of the initial respiratory infection, according to the ACCP guidelines 2
The ACCP guidelines explicitly state that if cough persists beyond 8 weeks following acute respiratory infection, diagnoses other than postinfectious cough must be considered 1, 2

Pathogenesis of upper airway cough syndrome involves persistent inflammation of nose and paranasal sinuses following the viral infection, and the American College of Chest Physicians recommends looking for throat clearing, sensation of postnasal drip, nasal discharge, or rhinosinusitis symptoms 1, 2, 3
Asthma is a critical diagnosis not to miss, as it is commonly misdiagnosed as acute bronchitis in approximately one-third of patients presenting with acute cough, according to the American Thoracic Society 4
Approximately 40% of previously healthy individuals develop transient bronchial hyperresponsiveness after acute respiratory infections, though this typically resolves within 6 weeks, as reported by the American College of Chest Physicians 5
In retrospective studies, 65% of patients with recurrent "acute bronchitis" episodes actually had mild asthma, according to the American Thoracic Society 4
Gastroesophageal reflux disease may be triggered or exacerbated by vigorous coughing from the initial viral illness, and the American Gastroenterological Association recommends looking for heartburn, regurgitation, or cough worsening after meals or when supine 2, 3

Bordetella pertussis infection must be considered if paroxysms of coughing, post-tussive vomiting, or inspiratory whooping sound are present, according to the Centers for Disease Control and Prevention 1, 2
Diagnosis of Bordetella pertussis infection should be made when cough lasts >2 weeks with these characteristic features unless another diagnosis is proven, as recommended by the Centers for Disease Control and Prevention 1, 2

Chest radiograph is essential to rule out pneumonia, malignancy, or other structural abnormalities, according to the American College of Chest Physicians 4
Spirometry is recommended to evaluate for asthma or obstructive lung disease, as suggested by the American Thoracic Society 4
Clinical assessment for upper airway cough syndrome symptoms (rhinosinusitis, postnasal drip) is necessary, according to the American College of Chest Physicians 1, 2

Do not assume this is still "postinfectious cough" at 3 months duration—this diagnosis is only valid for 3-8 weeks post-infection, as stated by the American College of Chest Physicians 1, 2
Do not prescribe antibiotics unless bacterial sinusitis or pertussis is specifically suspected, as viral etiology accounts for >90% of initial bronchitis cases, according to the American Thoracic Society 4
Do not miss underlying asthma, which is the most commonly overlooked diagnosis in patients with recurrent "bronchitis", as reported by the American Thoracic Society 4, 5