What is post-infectious cough in an adult with a history of respiratory infections, asthma, or chronic obstructive pulmonary disease (COPD)?

What is Post-Infectious Cough?

Post-infectious cough is a subacute cough that persists for 3 to 8 weeks following an upper respiratory tract infection, occurring after the acute infectious symptoms have resolved, with a normal chest radiograph and eventual self-resolution. 1

Definition and Timeline

Post-infectious cough represents a distinct clinical entity that bridges acute and chronic cough:

• Duration: The cough must persist for at least 3 weeks but not exceed 8 weeks after the initial respiratory infection 1
• Classification: This places it in the "subacute cough" category, distinguishing it from acute cough (<3 weeks) and chronic cough (>8 weeks) 1, 2
• Diagnostic criteria: Chest radiograph must be normal, ruling out pneumonia or other structural lung disease 1
• Natural history: The condition is self-limited and eventually resolves spontaneously, though this can be frustrating for patients 1, 2

Pathophysiology

The mechanism underlying post-infectious cough involves extensive airway damage and inflammation:

• Epithelial disruption: Respiratory viruses cause widespread desquamation of epithelial cells down to the basement membrane, as demonstrated in influenza A infections 1
• Inflammatory infiltrate: Bronchoscopy reveals increased lymphocytes and neutrophils in bronchoalveolar lavage fluid, with lymphocytic infiltration on biopsy 1
• Notably absent: Eosinophilic inflammation (typical of asthma) is NOT present, helping distinguish this from asthma exacerbations 1
• Lower airway involvement: When originating from the lower airways, there is excessive mucus hypersecretion, impaired mucociliary clearance, and transient airway hyperresponsiveness 1, 2
• Cough receptor sensitivity: Paradoxically, despite symptomatic heightened coughing, capsaicin challenge testing shows variable results—not consistently elevated in all post-infectious coughs 1

Clinical Context in High-Risk Populations

For adults with asthma, COPD, or recurrent respiratory infections, several important considerations apply:

• Multifactorial pathogenesis: The cough mechanism frequently involves multiple contributing factors simultaneously 1
• Upper airway involvement: Persistent inflammation of the nose and paranasal sinuses can lead to upper airway cough syndrome (previously called postnasal drip syndrome) 1
• GERD complication: Vigorous coughing itself can trigger or worsen gastroesophageal reflux disease, creating a vicious cycle 1
• Transient hyperresponsiveness: Patients may develop temporary bronchial hyperresponsiveness without having underlying asthma 1

Critical Differential Diagnosis: Bordetella Pertussis

A particularly virulent form of post-infectious cough is caused by Bordetella pertussis, which requires specific recognition and treatment:

• Clinical clues: Paroxysms of coughing, post-tussive vomiting, and/or inspiratory whooping sound should trigger immediate consideration of pertussis 1
• Diagnostic approach: When these features are present, assume pertussis unless another diagnosis is proven 1
• Contagiousness: This infection is highly contagious and requires patient isolation 1
• Treatment window: Responds to oral macrolide antibiotics, but only when administered early in the disease course 1
• Duration despite treatment: Even with appropriate antibiotics, the cough typically persists for 2-6 weeks and can last for months, as the antibiotics prevent transmission but don't modify the cough course once established 3
• Vaccination: Safe and effective vaccines are available for adults and should be administered per CDC guidelines 1

Management Algorithm

The ACCP guidelines provide a structured approach to managing post-infectious cough:

Step 1: Identify Contributing Factors 1

Before initiating therapy, determine which pathogenetic factors are most likely:

• Postviral airway inflammation with mucus hypersecretion
• Bronchial hyperresponsiveness
• Upper airway cough syndrome (UACS)
• Asthma (new or exacerbated)
• Gastroesophageal reflux disease

Step 2: Antibiotic Decision 1, 2

Antibiotics have NO role except in two specific situations:

• Bacterial sinusitis is confirmed
• Early Bordetella pertussis infection is diagnosed

Step 3: Pharmacologic Management

First-line: Inhaled ipratropium bromide 1, 2

• This is the only inhaled agent with evidence for attenuating post-infectious cough
• May be particularly helpful when lower airway involvement with mucus hypersecretion is present

Second-line: Inhaled corticosteroids 3, 2

• Consider when ipratropium fails to provide adequate relief
• Evidence comes from uncontrolled studies but may be tried for protracted, persistently troublesome cough

Third-line: Central-acting antitussives 3

• Codeine or dextromethorphan should be considered when other measures fail
• Reserved for symptomatic relief when cough significantly impacts quality of life

Oral corticosteroids 2

• May be tried for protracted cases, though evidence is limited to uncontrolled studies

Common Pitfalls to Avoid

Critical mistake #1: Missing pertussis 3, 2

• Do not dismiss pertussis in vaccinated individuals—breakthrough infections occur
• The infectious period can exceed 6 weeks if untreated
• Early diagnosis, treatment, and contact prophylaxis are essential to prevent transmission

Critical mistake #2: Inappropriate antibiotic use 1, 2

• Most post-infectious coughs are viral and do not benefit from antibiotics
• Antibiotics should not be prescribed for "over-peak cough" without confirmed bacterial infection

Critical mistake #3: Failing to reassess at key timepoints 2

• At 3 weeks: Begin considering alternative diagnoses including pertussis, Mycoplasma/Chlamydophila pneumoniae, UACS, and GERD
• At 8 weeks: The cough is now chronic and requires full diagnostic workup for asthma, chronic sinusitis, GERD, and other chronic pulmonary conditions

Prognosis and Patient Counseling

Reassure patients that post-infectious cough is self-limited: 2

• 90% of patients experience resolution within 3 weeks 2
• Approximately 10% will continue coughing for more than 20-25 days even with appropriate therapy 2
• Most cases resolve within the 3-8 week window 1, 2

For specific pathogens, expected durations are: 2

• Mycoplasma pneumoniae: mean 23 days
• Chlamydophila pneumoniae: mean 26 days
• Pertussis (unvaccinated): median 52-61 days
• Pertussis (vaccinated): median 29-39 days