What are the diagnostic methods and treatment options for whooping cough (pertussis)?

Whooping Cough (Pertussis): Diagnosis and Treatment

Clinical Diagnosis

Diagnose pertussis clinically when a patient presents with cough lasting ≥2 weeks accompanied by paroxysms of coughing, post-tussive vomiting, and/or inspiratory whooping sound—do not wait for laboratory confirmation to initiate treatment. 1

Key Clinical Features

• Catarrhal stage (1-2 weeks): Nonspecific symptoms including nasal congestion, runny nose, mild sore throat, mild dry cough, and minimal or no fever that are indistinguishable from minor respiratory infections 1
• Paroxysmal stage (2-6 weeks): Successive coughs without inspiration, terminating with inspiratory "whoop" and often followed by post-tussive vomiting; patients appear well between episodes 1
• Convalescent stage (2-6+ weeks): Gradual decrease in paroxysm frequency and severity 1

Important Clinical Pearls

• The classic "whoop" may be absent in previously vaccinated children, adolescents, and adults 1
• Infants can present atypically with apneic spells and minimal cough 1
• Fever does NOT exclude pertussis 2
• Post-tussive vomiting has 60% sensitivity and 66% specificity for pertussis 2

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Diagnostic Testing

First-Line Test

Order a nasopharyngeal aspirate or Dacron swab for culture immediately—bacterial isolation is the only certain way to confirm diagnosis. 1, 2

• Culture requires enriched media and has 25-50% sensitivity 1
• Obtain specimen as early as possible, ideally during catarrhal or early paroxysmal stage 1

Alternative Testing

• PCR testing: Available with 80-100% sensitivity and high specificity, but not universally standardized for routine clinical use 1
• Serology: Paired acute and convalescent sera showing fourfold increase in IgG or IgA antibodies to pertussis toxin (PT) or filamentous hemagglutinin (FHA) can provide presumptive diagnosis 1
  • First sample within 2 weeks of cough onset, second sample 3-4 weeks later 1
  • Sensitivity 63%, specificity 99% for community outbreaks 1
  • Not validated or approved for routine diagnostic use in the United States 1

Confirmed Diagnosis Criteria

A confirmed case requires either: 1

• Isolation of B. pertussis from nasopharyngeal culture, OR
• Compatible clinical picture with epidemiologic linkage to a confirmed case

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Treatment Protocol

Immediate Actions

Start azithromycin immediately upon clinical suspicion without waiting for diagnostic confirmation—early treatment within the first few weeks diminishes coughing paroxysms, prevents complications, and stops disease transmission. 1, 3, 2

Isolate the patient for 5 days from the start of antibiotic treatment. 1, 3, 2

First-Line Antibiotic: Azithromycin

Azithromycin is the preferred macrolide for all age groups due to superior tolerability, better compliance, equal efficacy to erythromycin, and significantly lower risk of infantile hypertrophic pyloric stenosis (IHPS). 3

Dosing: 3

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

Critical precaution: Do not administer with aluminum- or magnesium-containing antacids as they reduce absorption 3

Second-Line: Erythromycin

Use erythromycin only when azithromycin is unavailable; avoid in infants <6 months due to IHPS risk. 1, 3

Dosing: 1, 3

• Children: 40-50 mg/kg/day in divided doses for 14 days
• Adults: 1-2 g/day in divided doses for 14 days

Critical precaution: Erythromycin inhibits cytochrome P450 enzyme system—check for drug interactions 3

Alternative for Macrolide Contraindications

Trimethoprim-sulfamethoxazole for patients >2 months with macrolide contraindications or hypersensitivity. 1, 3

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Treatment Timing and Expected Outcomes

Early Treatment (Catarrhal Phase: First 2 Weeks)

• Maximum clinical benefit: Rapidly clears bacteria from nasopharynx, reduces coughing paroxysms, and prevents complications 3
• This is the critical window for symptom modification 3

Late Treatment (Paroxysmal Phase: >3 Weeks)

• Limited clinical benefit for symptom reduction, but still indicated to prevent transmission to others 3
• 80-90% of untreated patients spontaneously clear B. pertussis within 3-4 weeks 3
• Cough may persist for weeks to months despite appropriate antibiotic treatment, but patient is no longer contagious after 5 days of antibiotics 3

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Postexposure Prophylaxis

Use the same antibiotic regimens and dosing as for treatment. 3

Indications for Prophylaxis

Administer within 21 days of exposure to: 3

• All household contacts
• High-priority groups: infants <12 months, pregnant women in third trimester, healthcare workers with known exposure

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Isolation and Return to Activities

With antibiotics: Patients may return to school/work after 5 days of treatment 3

Without antibiotics: Patients must remain isolated for 21 days after cough onset 3

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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

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Vaccination Recommendations

• All children: Complete DTaP primary vaccination series (5 doses at 2,4,6,15-18 months, and 4-6 years) followed by single Tdap booster in early adolescence 1
• Adults up to age 65: Single dose Tdap vaccine according to CDC guidelines 1
• Pregnant women: Tdap between 27-36 weeks' gestation with each pregnancy to convey immunity to newborn 3
• Household contacts: Ensure all contacts, especially infants, are up to date on pertussis vaccination 3, 2

Critical Vaccination Context

• Vaccine immunity wanes after 5-10 years, making previously vaccinated individuals susceptible 3
• Secondary attack rate exceeds 80% among susceptible persons 1
• Unvaccinated or incompletely vaccinated infants <12 months have highest risk for severe complications and death 1

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Public Health Reporting

Report both probable and confirmed cases to public health authorities. 1