What is the best course of action for a patient presenting with a cough lasting three weeks?

Management of a Patient with 3-Week Cough

Your patient has a subacute cough (defined as 3-8 weeks duration), and the most important first step is to determine if this followed a recent respiratory infection—if so, treat as postinfectious cough; if not, or if red flags are present, pursue urgent evaluation for serious causes. 1

Immediate Assessment: Screen for Life-Threatening Conditions

Before anything else, actively look for these red flags that demand urgent investigation 1, 2:

• Hemoptysis (any amount)
• Vital sign abnormalities: Heart rate ≥100 bpm, respiratory rate ≥24 breaths/min, temperature ≥38°C 2
• Asymmetrical lung sounds or focal consolidation on examination 2
• Systemic symptoms: Fever, unintentional weight loss, night sweats 1
• Smoker >45 years with new or changed cough 1
• Prominent dyspnea, especially at rest or night 1

If any red flags are present: Order chest X-ray immediately and consider pneumonia, tuberculosis (especially in endemic areas or high-risk populations), pulmonary embolism, heart failure, or malignancy. 1, 2

Determine the Clinical Context

Was There a Preceding Respiratory Infection?

If YES (most common scenario): This is likely postinfectious cough 1

The most common causes in this category are 1:

• Postinfectious inflammation (48.4% of cases)
• Upper airway cough syndrome/postnasal drip (33.2%)
• Asthma exacerbation (15.8%)
• Nonasthmatic eosinophilic bronchitis (5.4%)

If NO clear preceding infection: Evaluate as you would chronic cough, even though duration is only 3 weeks 1

Critical Diagnostic Consideration: Rule Out Pertussis

Suspect pertussis immediately if ANY of these features are present 3, 2:

• Paroxysmal coughing episodes (cough lasting ≥2 weeks with paroxysms is pertussis until proven otherwise) 3
• Post-tussive vomiting
• Inspiratory whooping sound
• Recent exposure to confirmed pertussis case 2

If Pertussis is Suspected:

Start treatment immediately WITHOUT waiting for laboratory confirmation 3:

• Azithromycin (preferred first-line due to better tolerability) 3
• Alternative: Erythromycin 1-2 g/day for 2 weeks or clarithromycin 3
• Isolate patient for 5 days from start of antibiotics 3
• Obtain nasopharyngeal aspirate or Dacron swab for culture (bacterial isolation is the only definitive confirmation) 3, 2
• Consider paired serology (IgG/IgA against pertussis toxin) for 4-fold increase between acute and convalescent phases 3, 2

Critical pitfall: Early treatment (within first 2 weeks) decreases paroxysms and prevents transmission; after 2 weeks, benefit is limited but may still be offered 3. Delay in treatment significantly reduces effectiveness 3.

Treatment Algorithm for Postinfectious Cough (No Pertussis Features)

First-Line Treatment:

Inhaled ipratropium is the first-line treatment for postinfectious cough 1, 3

If Ipratropium Fails or Severe Symptoms:

• Dextromethorphan 60 mg (this is the optimal dose for cough reflex suppression—over-the-counter doses are subtherapeutic) 3
• Prednisone 30-40 mg/day for a short period if severe paroxysms persist 3

Critical pitfall: Do NOT use subtherapeutic doses of dextromethorphan; doses available over the counter are insufficient 3. Do NOT use codeine—it has no greater efficacy but worse side effects 3.

If Upper Airway Symptoms Predominate (Postnasal Drip):

• First-generation antihistamine PLUS decongestant has been shown in double-blind placebo-controlled studies to decrease cough severity and hasten resolution 1

Antibiotics Have NO Role:

Do NOT prescribe antibiotics for postinfectious viral cough unless bacterial sinusitis or early pertussis is confirmed 1, 3. Except for these specific conditions, antibiotics are ineffective and contribute to resistance 1.

Medication Review

Check if patient is taking an ACE inhibitor 2, 4:

• ACE inhibitors cause persistent cough
• Stop the medication immediately if present 2
• Median time to cough resolution after stopping is 26 days 2

Geographic and Risk-Based Considerations

In TB-endemic areas or high-risk populations (immigrants from high-prevalence countries, HIV-positive, homeless, incarcerated), consider tuberculosis even with normal chest X-ray 1, 2:

• Obtain chest radiograph
• Collect sputum smears and cultures for acid-fast bacilli 2
• TB should be considered but not to the exclusion of more common causes 4

Follow-Up and Monitoring

Routinely assess cough severity or quality of life using a validated tool before and after treatment 1

Schedule follow-up in 4-6 weeks 1:

• If cough persists beyond 8 weeks, it becomes chronic cough and requires full chronic cough workup (chest X-ray, spirometry, systematic evaluation for upper airway cough syndrome, asthma, GERD, nonasthmatic eosinophilic bronchitis) 1, 4

Critical pitfall: Do NOT classify as chronic cough before 8 weeks—at 3 weeks, this is still subacute phase with different diagnostic and therapeutic approach 3.