What are the symptoms and treatment of pertussis (whooping cough)?

Whooping Cough (Pertussis): Symptoms and Treatment

Clinical Presentation

Pertussis presents in three distinct phases: the catarrhal phase (1-2 weeks) with nonspecific cold-like symptoms, the paroxysmal phase (4-6 weeks) with characteristic severe coughing fits, and the convalescent phase (2-6 weeks or longer) with gradual improvement. 1

Catarrhal Phase (First 1-2 Weeks)

• Nonspecific symptoms including runny nose, sneezing, watery eyes, and mild intermittent cough 1
• Minimal or no fever 1
• Most contagious during this phase, yet symptoms are least specific 1
• Clinically indistinguishable from common respiratory infections 1

Paroxysmal Phase (4-6 Weeks)

• Paroxysmal cough: rapid series of expiratory bursts followed by sudden loud inspiratory sound (the "whoop") 1
• Post-tussive vomiting (vomiting after coughing fits) 1
• Inspiratory whooping sound 1
• Important caveat: The classic "whoop" is frequently absent in adults and previously vaccinated individuals 1
• Physical examination between coughing episodes is often surprisingly unremarkable 1

Convalescent Phase (2-6 Weeks or Longer)

• Gradual improvement with decreasing frequency of coughing bouts 1
• Nonparoxysmal cough can persist for months 1

Age-Specific Variations

• Infants may present atypically with apneic spells (breathing pauses) and minimal cough rather than the classic whoop 1
• Infants are at highest risk for severe complications including pneumonia, seizures, and death 2
• Adolescents and adults often have prolonged cough without the characteristic whoop 1

Diagnostic Approach

When a patient has cough lasting ≥2 weeks with paroxysmal episodes, post-tussive vomiting, and/or inspiratory whooping, diagnose pertussis unless another diagnosis is proven. 3, 4

Clinical Diagnosis

• Paroxysmal cough has high sensitivity (93.2%) but low specificity (20.6%) - its absence makes pertussis unlikely 1
• Post-tussive vomiting has high specificity (77.7%) - when present, strongly suggests pertussis 1
• Inspiratory whoop has high specificity (79.5%) - when present, strongly suggests pertussis 1
• Absence of fever supports the diagnosis 1

Laboratory Confirmation

• Nasopharyngeal aspirate or Dacron swab for culture is the definitive diagnostic test 3, 4
• PCR testing of nasopharyngeal specimens is the preferred confirmatory test in modern practice 1
• Culture has 100% specificity but isolation of bacteria is the only certain way to confirm diagnosis 3
• Serology showing fourfold increase in IgG or IgA antibodies can provide presumptive diagnosis 3
• Do not wait for laboratory confirmation to initiate treatment 5, 1, 4

Treatment

Start macrolide antibiotics immediately upon clinical suspicion without waiting for laboratory confirmation, as early treatment (within first 2 weeks) rapidly clears B. pertussis from the nasopharynx and decreases coughing paroxysms. 5, 4

First-Line Antibiotic Therapy

Azithromycin is the preferred first-line agent for all age groups due to better tolerability and convenient dosing: 5

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

Alternative Antibiotics

• Clarithromycin is equally effective as azithromycin 5
• Erythromycin 1-2 g/day in adults for 14 days is an alternative, but avoid in infants <6 months due to association with infantile hypertrophic pyloric stenosis (IHPS) 5
• Trimethoprim-sulfamethoxazole for 7 days is recommended for patients >2 months with macrolide contraindications 5

Critical Treatment Timing

• Early treatment during the catarrhal phase (first 2 weeks) is critical for effectiveness 5
• Treatment after 3 weeks has limited clinical benefit but is still indicated to prevent transmission 5
• Antibiotics eliminate B. pertussis but do not alter the clinical course if started late 6
• Approximately 80-90% of untreated patients spontaneously clear the organism within 3-4 weeks 5

Isolation Requirements

Isolate patients at home and away from work/school for 5 days after starting antibiotics to prevent transmission 3, 5, 4

Treatments That Do NOT Work

Do not use β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin - these have no proven benefit in controlling coughing paroxysms 3, 5

Symptomatic Management for Post-Infectious Cough

If cough persists beyond the acute infection:

• Inhaled ipratropium may attenuate the cough 3, 4
• For severe paroxysms, consider prednisone 30-40 mg/day for a short period after ruling out other causes 3, 4
• Central-acting antitussives (codeine or dextromethorphan 60 mg) when other measures fail 3, 4

Postexposure Prophylaxis

Use the same antimicrobial agents and dosing regimens for prophylaxis as for treatment 5

Prioritize prophylaxis for: 5

• All household contacts
• Infants <12 months
• Women in third trimester of pregnancy
• Close contacts in exposure settings with vulnerable populations

Prevention

All children should receive complete DTaP (diphtheria, tetanus, acellular pertussis) primary vaccination series followed by Tdap booster in adolescence 3

All pregnant patients should receive Tdap between 27-36 weeks' gestation with each pregnancy to convey immunity to the newborn 7

Common Pitfalls to Avoid

• Do not wait for laboratory confirmation to start treatment - delay decreases effectiveness and allows continued transmission 5, 4
• Do not dismiss pertussis in vaccinated adolescents and adults - illness can be milder with absent whoop in previously vaccinated individuals 1
• Do not overlook infants with atypical presentation - they may have apneic spells rather than classic cough 1
• Do not use erythromycin in infants <6 months - significant risk of IHPS 5
• Do not forget isolation for 5 days after starting antibiotics - patients remain contagious 3, 5, 4
• Do not administer azithromycin simultaneously with aluminum- or magnesium-containing antacids as they reduce absorption 5