What is the recommended treatment for an adult diagnosed with pertussis (whooping cough)?

Treatment of Pertussis in Adults

First-Line Antibiotic Treatment

Adults with confirmed or suspected pertussis should receive azithromycin 500 mg on day 1, followed by 250 mg daily on days 2-5, as this is the preferred macrolide antibiotic due to superior tolerability, better compliance, and equal efficacy compared to erythromycin. 1, 2, 3

Why Azithromycin is Preferred

• Azithromycin has significantly higher completion rates (93%) compared to erythromycin (57%), primarily due to fewer gastrointestinal side effects 4
• The shorter 5-day course improves adherence compared to the 14-day erythromycin regimen 1, 3
• Azithromycin does not inhibit cytochrome P450 enzymes, avoiding drug interactions that occur with erythromycin and clarithromycin 3
• Clinical trials demonstrate equal microbiologic eradication rates between azithromycin and erythromycin (100% vs 96%) 5, 6

Alternative Macrolide Options

• Clarithromycin can be used as an alternative: 500 mg twice daily for 7 days 1, 3
• Erythromycin should only be used when azithromycin is unavailable: 500 mg four times daily for 14 days 1, 7
• Erythromycin causes uncomfortable gastrointestinal side effects in 76% of patients, with 91% reporting gastrointestinal upset 4

For Macrolide-Intolerant Patients

• Trimethoprim-sulfamethoxazole (TMP-SMZ) is the alternative for patients with macrolide contraindications or hypersensitivity 1, 3

Critical Timing Considerations

Start antibiotics immediately upon clinical suspicion without waiting for diagnostic confirmation, as early treatment during the catarrhal phase (first 2 weeks) rapidly clears B. pertussis from the nasopharynx, decreases coughing paroxysms, and reduces complications. 1, 2, 3

Treatment Effectiveness by Disease Stage

• Early treatment (catarrhal phase, first 2 weeks): Maximum clinical benefit—reduces duration and severity of symptoms by approximately 50% 1, 2, 3
• Late treatment (paroxysmal phase, >3 weeks): Limited clinical benefit for symptom reduction, but still indicated to prevent transmission to others 1, 2, 3
• Antibiotic treatment generally does not modify the course of illness after cough onset, but is essential for infection control 1
• Approximately 80-90% of untreated patients spontaneously clear B. pertussis within 3-4 weeks from cough onset 1, 3

Isolation and Infection Control

Isolate patients at home and away from work/school for 5 days after starting antibiotics to prevent transmission, as pertussis is highly contagious with secondary attack rates exceeding 80% among susceptible contacts. 1, 2, 3

• Without antibiotics, patients must remain isolated for 21 days after cough onset 2, 3
• Patients can return to work/school after completing 5 days of antibiotic treatment 2, 3

Postexposure Prophylaxis for Contacts

Use the same antibiotic regimens and dosing as for treatment (azithromycin 500 mg day 1, then 250 mg days 2-5) for all close contacts within 21 days of exposure. 1, 2, 3

High-Priority Groups Requiring Prophylaxis

• All household contacts regardless of vaccination status 2, 3
• Infants <12 months (highest risk for severe complications and death) 1
• Pregnant women in third trimester 2, 3, 8
• Healthcare workers with known exposure 2

Diagnostic Confirmation

Obtain nasopharyngeal aspirate or Dacron swab for culture to confirm diagnosis, though treatment should not be delayed while awaiting results. 1, 2, 3

• Culture is the only certain way to make the diagnosis 1, 3
• PCR testing has replaced culture as the preferred confirmatory test in clinical practice 8
• Suspect pertussis when cough lasts ≥2 weeks with paroxysms, post-tussive vomiting, and/or inspiratory whooping 1, 2

Therapies to Avoid

Do not use β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin, as these have no proven benefit in controlling coughing paroxysms or improving outcomes. 1, 2, 3

• These adjunctive therapies are ineffective for symptom control despite theoretical rationale 1, 3

Important Drug Interactions and Precautions

• Azithromycin should not be taken with aluminum- or magnesium-containing antacids as they reduce absorption 2, 3
• Erythromycin and clarithromycin (but NOT azithromycin) inhibit cytochrome P450 enzymes and can interact with digoxin, triazolam, and ergot alkaloids 1, 3
• Obtain baseline ECG before initiating azithromycin in patients taking medications that prolong QTc interval (e.g., citalopram) 3

Vaccination Considerations

• Vaccine immunity wanes after 5-10 years, making previously vaccinated adults susceptible to infection 1
• Neither vaccination nor natural disease confers lifelong protective immunity 1
• Adults up to age 65 should receive a single dose of Tdap vaccine according to CDC guidelines 1
• Pregnant women should receive Tdap between 27-36 weeks' gestation with each pregnancy to convey immunity to the newborn 2, 8

Common Pitfalls to Avoid

• Do not delay treatment waiting for culture confirmation—start antibiotics immediately upon clinical suspicion 1, 2, 3
• Do not assume vaccination provides complete protection—breakthrough infections occur due to waning immunity 1
• Do not discontinue antibiotics early even if symptoms persist—the primary goal is eradication of bacteria and prevention of transmission, not symptom relief 1, 2, 3
• Do not forget to treat all household contacts—prophylaxis is essential regardless of vaccination status 2, 3