Whooping cough

Definition
Whooping cough, or pertussis, is a highly contagious respiratory infection caused by Bordetella pertussis, a gram-negative coccobacillus. It is characterized by severe coughing spells followed by a “whooping” sound during the subsequent rapid inhalation.

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Causative Agent

• Bordetella pertussis (primary cause)

• Occasionally Bordetella parapertussis (usually milder illness)

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Transmission

• Spread via respiratory droplets from coughing or sneezing

• Incubation period: 7–10 days (range 5–21 days)

• Highly contagious during the catarrhal stage and early paroxysmal stage

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Pathogenesis

• Bacteria attach to ciliated respiratory epithelial cells using adhesins (e.g., filamentous hemagglutinin)

• Release toxins (pertussis toxin, tracheal cytotoxin, adenylate cyclase toxin) that damage cilia and impair mucociliary clearance

• This leads to persistent cough and airway inflammation

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Clinical Stages

1. Catarrhal Stage (1–2 weeks)

   • Resembles common cold: runny nose, sneezing, mild cough, low-grade fever

   • Most infectious stage

2. Paroxysmal Stage (1–6 weeks, may last up to 10 weeks)

   • Severe coughing fits followed by inspiratory “whoop”

   • Post-tussive vomiting

   • Apnea, especially in infants (may be life-threatening)

3. Convalescent Stage (weeks to months)

   • Gradual decrease in cough frequency and severity

   • Secondary respiratory infections may occur

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Complications

• Infants: Apnea, pneumonia, seizures, encephalopathy, death

• Older children/adults: Weight loss, rib fractures, urinary incontinence from severe coughing

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Diagnosis

• Clinical: Characteristic cough and history of contact

• Laboratory:

  • PCR for B. pertussis (most sensitive in early illness)

  • Culture from nasopharyngeal swab (gold standard but less sensitive)

  • Serology (useful in later stages)

• Leukocytosis with marked lymphocytosis is common in infants and young children

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Treatment

A. Antibiotic therapy – most effective if started during catarrhal stage, but still given later to reduce transmission

• First-line:

  • Azithromycin

    • Adults: 500 mg on day 1, then 250 mg once daily on days 2–5

    • Infants >1 month and children: 10 mg/kg on day 1 (max 500 mg), then 5 mg/kg once daily on days 2–5

  • Clarithromycin (alternative)

    • Adults: 500 mg twice daily for 7 days

    • Children: 15 mg/kg/day in 2 doses for 7 days

  • Erythromycin (less preferred due to GI side effects)

    • Adults: 500 mg four times daily for 14 days

    • Children: 40–50 mg/kg/day in 4 doses for 14 days

• For infants <1 month: Azithromycin is preferred (erythromycin linked to infantile hypertrophic pyloric stenosis)

B. Supportive care

• Oxygen therapy for hypoxia

• Small frequent feeds to prevent vomiting-induced dehydration

• Close monitoring in infants for apnea and respiratory distress

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Prevention

• Vaccination:

  • DTaP (diphtheria, tetanus, acellular pertussis) – primary series in infants

  • Tdap booster at 11–12 years and in adults

  • Pregnant women: Tdap during each pregnancy (27–36 weeks gestation) to protect newborn

• Post-exposure prophylaxis:

  • Antibiotics (azithromycin, clarithromycin, or erythromycin) given to close contacts regardless of vaccination status, especially if contacts include infants or pregnant women

• Public health measures: Isolation of infected individuals for 5 days after starting antibiotics