What is the assessment and treatment approach for a patient presenting with symptoms of pertussis (whooping cough), considering their age, medical history, and vaccination status?

Assessment and Treatment of Suspected Pertussis (Whooping Cough)

For any patient with suspected pertussis, immediately obtain a nasopharyngeal swab for culture (gold standard) or PCR testing, and if confirmed or highly probable, start a macrolide antibiotic with 5 days of isolation to reduce transmission and potentially shorten symptoms if caught early. 1

Clinical Assessment: Key Diagnostic Features

Adults

When evaluating an adult with cough, specifically assess for these four critical features that help rule pertussis in or out: 1

• Paroxysmal cough (high sensitivity, low specificity) - absence makes pertussis unlikely 1
• Absence of fever (high sensitivity, low specificity) - presence of fever makes pertussis unlikely 1
• Posttussive vomiting (low sensitivity, high specificity) - presence strongly suggests pertussis 1
• Inspiratory whooping (low sensitivity, high specificity) - presence strongly suggests pertussis 1

Important caveat: Vaccinated adults often present with atypical symptoms, potentially lacking the characteristic "whoop" and experiencing milder manifestations. 2 The classic whoop is actually rare in adults (only 8%), but cough followed by vomiting/choking (53%) and sleep-disturbing cough (52%) are common. 3

Children

For children with acute cough (<4 weeks), assess for: 1

• Paroxysmal cough 1
• Posttussive vomiting (moderately sensitive and specific in children) 1
• Inspiratory whooping 1

Critical pitfall: Infants under 6 weeks may present atypically with apneic spells and minimal cough initially, rather than classic whooping. 4 This age group has the highest mortality risk (1.8% case-fatality ratio). 4

Vaccination Status Considerations

Do not dismiss pertussis based solely on vaccination status - breakthrough infections occur because immunity wanes 5-10 years after vaccination. 2, 5 Vaccinated individuals can still contract and transmit pertussis, though symptoms are typically 50% less severe and shorter in duration. 5

Diagnostic Testing

Definitive Diagnosis

Order a nasopharyngeal aspirate or Dacron swab for culture - isolation of Bordetella pertussis is the only certain way to make the diagnosis. 1

PCR testing is now the preferred confirmatory test in clinical practice (replacing culture), though guidelines note it lacks universally validated standardization. 1, 6 PCR is faster and more practical than culture. 6

Presumptive Diagnosis

For suspected cases, order paired acute and convalescent sera - a fourfold increase in IgG or IgA antibodies to pertussis toxin (PT) or filamentous hemagglutinin (FHA) indicates recent infection. 1

Confirmed diagnosis requires either: 1

• Positive nasopharyngeal culture, OR
• Compatible clinical picture with epidemiologic linkage to a confirmed case

Treatment Protocol

Antibiotic Therapy

Start a macrolide antibiotic immediately for confirmed or probable pertussis: 1

First-line: Azithromycin (preferred due to better tolerability and compliance) 5, 6

• Adults: 500 mg day 1, then 250 mg daily for 4 days 2
• Children: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) daily for 4 days 5

Alternatives: 2

• Erythromycin: 1g/day adults, 40-50 mg/kg/day children for 14 days
• Clarithromycin: 500 mg twice daily adults, 15-20 mg/kg/day divided twice daily children for 10-14 days

For macrolide allergy/intolerance: 2

• Trimethoprim-sulfamethoxazole: 320mg/1600mg daily adults, 8mg/40mg/kg/day children for 14 days

Timing Is Critical

Early treatment (within first few weeks) will diminish coughing paroxysms and prevent spread; treatment beyond this period may be offered but is unlikely to help the patient's symptoms, though it still reduces transmission. 1 Even when started during the paroxysmal stage, antibiotics remain critical for reducing transmission to others. 5

Isolation Requirements

Isolate patients for 5 days from the start of antibiotic treatment. 1 If antibiotics cannot be administered, isolation should continue for 21 days after cough onset. 5

Therapies to AVOID

Do not offer long-acting β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin - there is no evidence these benefit patients with whooping cough. 1

Contact Management

Prophylaxis Protocol

All household and close contacts require macrolide antibiotic prophylaxis for 14 days, regardless of age and vaccination status. 2 This is critical because pertussis has secondary attack rates exceeding 80% among susceptible household contacts. 2, 5

Use the same macrolide regimens as for treatment. 2 Prophylaxis is most effective when initiated promptly after exposure. 2

Vaccination of Contacts

For close contacts <7 years who haven't completed the four-dose primary series, complete the series with minimal intervals. 2 Those who completed primary series but haven't received pertussis vaccine within 3 years of exposure should receive a booster dose. 2

High-Risk Populations Requiring Hospitalization

Infants under 6 months, especially under 2 months, require immediate hospitalization due to highest risk for severe complications including apnea, pneumonia, seizures, hypoxic encephalopathy, and death. 4 Hospital stays typically last 2-6 weeks depending on severity. 4

Other high-risk factors include: 4

• Prematurity (gestational age <37 weeks)
• Unvaccinated or incompletely vaccinated status

Common Pitfalls to Avoid

1. Don't assume typical presentation - vaccinated individuals and adults often lack the classic "whoop" 1, 2
2. Don't delay testing while waiting for classic symptoms - early intervention reduces transmission 5
3. Don't forget contact prophylaxis - this is essential to prevent household spread 2
4. Don't rely on vaccination history to exclude diagnosis - breakthrough infections are common 2, 5
5. Don't miss atypical presentation in young infants - apnea may be the only initial symptom 4