What is the management, including testing and post-exposure prophylaxis (PEP) with antibiotics, for patients exposed to someone diagnosed with pertussis (whooping cough), especially high-risk individuals like infants, pregnant women, and those with underlying health conditions?

Management of Pertussis Exposure

All close contacts of confirmed pertussis cases should receive post-exposure prophylaxis (PEP) with azithromycin within 21 days of exposure, regardless of vaccination status, with priority given to household contacts, infants under 12 months, pregnant women in their third trimester, and healthcare workers. 1

Who Qualifies as a Close Contact Requiring PEP

Close contacts are defined as individuals who have had direct contact with respiratory secretions from a pertussis case during the infectious period (catarrhal stage through first 3 weeks of cough, or until 5 days after starting antibiotics). 1

Priority groups for PEP include:

• All household contacts (strongly recommended by CDC) 1
• Infants under 12 months, especially those under 4 months who are at highest risk of severe complications and death 1, 2
• Pregnant women between 27-36 weeks gestation 1
• Healthcare workers with known exposure 1
• Childcare workers and others in close contact with high-risk individuals 3

Recommended Antibiotic Regimen for PEP

Azithromycin is the preferred agent for post-exposure prophylaxis due to superior tolerability, shorter treatment duration, and lower risk of infantile hypertrophic pyloric stenosis (IHPS) compared to erythromycin. 1

Azithromycin Dosing:

• Adults: 500 mg on day 1, then 250 mg daily for days 2-5 1
• Children ≥6 months: 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2-5 1, 2
• Infants <6 months: 10 mg/kg daily for 5 days 2

Alternative Agents:

• Clarithromycin: 500 mg twice daily for 7 days (adults); 7.5 mg/kg twice daily for 7 days (children) 1
• Trimethoprim-sulfamethoxazole: For patients >2 months with macrolide contraindications; one double-strength tablet twice daily for 14 days (adults); 8 mg/kg/day TMP in 2 divided doses for 14 days (children) 4, 2

Critical caveat: Erythromycin should be avoided in infants under 6 months due to association with IHPS. 2

Timing of PEP Administration

PEP must be administered within 21 days of exposure to be effective. 1 The goal is to eradicate B. pertussis from the nasopharynx of exposed individuals (whether symptomatic or asymptomatic) and prevent secondary transmission. 1

Pertussis is highly contagious with a secondary attack rate exceeding 80% among susceptible persons, making timely PEP critical. 1

Testing Strategy for Exposed Contacts

Do not wait for test results to initiate PEP in high-risk contacts or those with symptoms. 2

When to Test:

• Symptomatic contacts: Obtain nasopharyngeal swab (Dacron or flocked) for PCR testing if cough develops, as PCR has replaced culture as the preferred diagnostic test 5, 3
• Asymptomatic contacts: Routine testing is not recommended; focus on clinical monitoring 4

Monitoring Protocol:

• Asymptomatic contacts receiving PEP can continue normal activities, including work 4
• Healthcare workers who cannot receive PEP should be excluded from caring for children <4 years for 7-14 days post-exposure if mandated by state law 4
• Monitor all contacts for development of cough or respiratory symptoms for 21 days post-exposure 1, 3

Infection Control Measures

Implement respiratory droplet precautions:

• Wear surgical mask when within 3 feet of suspected or confirmed pertussis patient 4
• Isolate confirmed cases at home for 5 days after starting antibiotics 2, 5
• Limit patient movement and transport to essential purposes only 4

Vaccination Considerations

Verify and update vaccination status of all exposed contacts. 2, 5

• Tdap should be given to all individuals ≥11 years who have not received it previously 5
• Pregnant women should receive Tdap between 27-36 weeks gestation with each pregnancy, regardless of prior vaccination 5, 3
• Important limitation: Vaccination does not provide immediate protection and does not replace the need for PEP, as vaccine immunity wanes after 5-10 years 1, 5

Common Pitfalls to Avoid

Do not delay PEP while awaiting test results - the window for effective prophylaxis is narrow (21 days), and patients are most infectious during the catarrhal stage when symptoms are nonspecific. 1, 3

Do not rely on vaccination history alone - previously vaccinated individuals remain susceptible due to waning immunity, and immunized patients can still contract and transmit pertussis. 1, 5

Do not use erythromycin in young infants - azithromycin has a significantly lower risk of IHPS and is the preferred agent for infants <6 months. 2

Do not assume PEP provides long-term protection - antibiotic prophylaxis only addresses the immediate exposure; vaccination remains the most important long-term preventive strategy. 1