Azithromycin (Zithromax) is the Most Appropriate Empiric Therapy
This clinical presentation is classic for pertussis (whooping cough), and azithromycin should be initiated immediately without waiting for laboratory confirmation. 1, 2, 3
Clinical Diagnosis of Pertussis
The patient's presentation meets the diagnostic criteria for pertussis:
- Cough lasting >2 weeks with paroxysmal characteristics and post-tussive vomiting are the hallmark features that define pertussis clinically 1, 2, 3
- The initial mild upper respiratory prodrome (catarrhal phase) lasting approximately 10 days followed by worsening paroxysmal cough is the classic disease progression 2, 3
- Post-tussive vomiting has high specificity (77.7%) for pertussis—when present, it strongly suggests the diagnosis 3
- The absence of fever, clear lung examination, and normal chest radiograph are typical findings in pertussis, as the physical examination is often surprisingly unremarkable between coughing episodes 1, 3
Why Azithromycin is the Correct Choice
The American College of Chest Physicians explicitly states: "When the cough is accompanied by paroxysms of coughing, posttussive vomiting, and/or an inspiratory whooping sound, the diagnosis of B. pertussis infection should be made unless another diagnosis is proven." 1
- Macrolide antibiotics are the drugs of choice for pertussis treatment, with azithromycin preferred as first-line therapy 2, 4
- Treatment should be initiated immediately upon clinical suspicion without awaiting laboratory confirmation 2, 5
- Although antibiotics started after the catarrhal phase (which has already passed in this patient) will not significantly alter the clinical course, they are still essential to eradicate B. pertussis from the nasopharynx and prevent transmission to others 1, 2, 6
- The patient is currently in the most infectious period (first 3 weeks after cough onset), making prompt antibiotic therapy critical for public health 2, 3
Why the Other Options are Incorrect
- Prednisone (option a): Corticosteroids have no established role in adult pertussis management and are only considered in severe neonatal cases 7
- Antihistamines (option b): Not indicated for pertussis; the cough is due to airway inflammation and bacterial infection, not histamine-mediated processes 1
- Inhaled β-agonists (option c): While the ACCP guideline mentions that inhaled ipratropium (an anticholinergic, not a β-agonist) may be helpful for post-infectious cough with airway hyperresponsiveness, this patient's presentation is most consistent with active pertussis infection requiring antimicrobial therapy 1
- Immunoglobulin infusion (option d): Has no role in pertussis treatment; management relies on antibiotics and supportive care 2, 7
Critical Action Points
- Isolate the patient for 5 days after starting antibiotic therapy to prevent transmission 2, 3
- Identify and provide prophylaxis to close contacts, particularly household members and anyone at high risk (infants, pregnant women in third trimester, immunocompromised individuals) 2, 4
- Azithromycin dosing: Standard adult regimen is 500 mg on day 1, then 250 mg daily for days 2-5 4
Common Pitfall to Avoid
Do not dismiss pertussis in vaccinated adults. Neither vaccination nor natural infection confers lifelong immunity, with protective immunity waning 5-10 years after the last pertussis-containing vaccine dose. 2 The illness can present with milder symptoms and absent whoop in previously vaccinated individuals. 3