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

Treatment of Pertussis in Adults

Adults with pertussis should be treated with azithromycin 500 mg on day 1, followed by 250 mg daily on days 2-5, as this is the CDC-recommended first-line macrolide antibiotic with superior tolerability and compliance compared to erythromycin. 1

First-Line Antibiotic Treatment

Azithromycin is the preferred agent for all adults with pertussis due to equal efficacy to erythromycin but with significantly better tolerability, fewer side effects, and improved adherence to the treatment regimen. 1, 2

Dosing Regimen

• Azithromycin: 500 mg on day 1, then 250 mg daily on days 2-5 1, 2, 3
• Do not take azithromycin simultaneously with aluminum- or magnesium-containing antacids as they reduce absorption 2, 3

Alternative Macrolides

• Clarithromycin: Can be used as an alternative first-line agent with comparable efficacy 1
• Erythromycin: 1-2 g per day in divided doses for 14 days—only use when azithromycin is unavailable, as it causes uncomfortable to distressing side effects that result in poor adherence 1, 3

When Macrolides Cannot Be Used

For adults with macrolide contraindications or hypersensitivity, trimethoprim-sulfamethoxazole (TMP-SMZ) is the recommended alternative agent. 1, 2, 3

Timing of Treatment and Expected Outcomes

Early Treatment (Catarrhal Phase: First 2 Weeks)

• Maximum clinical benefit occurs when antibiotics are started early in the illness—macrolides administered during the catarrhal phase can reduce the duration and severity of symptoms and lessen the period of communicability 1, 2, 3
• Early treatment rapidly clears B. pertussis from the nasopharynx and decreases coughing paroxysms 1

Late Treatment (Paroxysmal Phase: >3 Weeks After Cough Onset)

• Antibiotic treatment generally does not modify the course of illness after the onset of cough, but is still recommended to prevent transmission 1
• Late treatment has limited clinical benefit for symptom reduction but remains critical for eradicating bacterial carriage and preventing spread to others 2, 3
• Approximately 80-90% of untreated patients will spontaneously clear B. pertussis from the nasopharynx within 3-4 weeks from cough onset 1, 2

Important Reality Check

The cough may persist for weeks to months despite appropriate antibiotic treatment—this is because the paroxysmal cough is caused by toxin-mediated damage to respiratory epithelium, not active infection. However, the patient is no longer contagious after 5 days of antibiotics. 2, 3

Isolation and Return to Work

• Isolate the patient at home and away from work for 5 days after starting antibiotics to prevent transmission 1, 2, 3
• Pertussis is highly infectious with secondary attack rates exceeding 80% among susceptible household contacts 1, 4
• Without antibiotics, isolation must continue for 21 days after cough onset 3, 4

Postexposure Prophylaxis for Contacts

Use the same antibiotic regimens and dosing as for treatment when providing prophylaxis to close contacts. 1, 2, 3

High-Priority Groups Requiring Prophylaxis

• All household and close contacts, regardless of vaccination status 2, 3, 4
• Infants <12 months (highest risk for severe complications and death) 1
• Pregnant women in the third trimester 2, 3
• Healthcare workers with known exposure 2

Timing

• Prophylaxis should be administered within 21 days of exposure 2, 3

Common Pitfalls and Important Caveats

Don't Wait for Diagnostic Confirmation

Start antibiotics immediately upon clinical suspicion of pertussis—do not wait for culture or PCR confirmation. 2, 3 The diagnosis is often missed in adults because the characteristic "whoop" may be absent and symptoms can be mild. 5

Drug Interactions to Consider

• Erythromycin and clarithromycin (but NOT azithromycin) inhibit the cytochrome P450 enzyme system and can interact with other medications metabolized by this pathway, including digoxin, triazolam, and ergot alkaloids 2, 3
• Azithromycin does NOT inhibit cytochrome P450 enzymes, making it safer in patients on multiple medications 2

Therapies That Don't Work

Do not use β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin—these have no proven benefit in controlling coughing paroxysms or improving outcomes in adults. 1, 2, 4

Erythromycin Resistance

Erythromycin resistance remains rare (<1%), so treatment failure is unlikely to be due to resistance. 2

Clinical Presentation in Adults

Adults with pertussis experience a protracted cough illness that can require hospitalization, with the majority coughing for >3 weeks and some for many months. 1 Common complications include:

• Pneumonia (up to 5%) 1
• Rib fracture from paroxysmal coughing (up to 4%) 1
• Loss of consciousness/cough syncope (up to 3-6%) 1
• Urinary incontinence (commonly reported in women) 1
• Other pressure-related complications: pneumothorax, subconjunctival hemorrhage, herniated disc 1

Adults with pertussis miss work for a mean of 7-10 days, with some unable to work for more than 1 month. 1