Pertussis (Whooping Cough) - Causes, Treatment & When to See a Doctor

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What is Pertussis (Whooping Cough)?

Pertussis, commonly known as whooping cough, is a contagious respiratory infection caused by the bacterium Bordetella pertussis. The disease is characterized by severe, hacking coughs that end in a high‑pitched “whoop” sound when the person inhales. While it can affect individuals of any age, infants and young children are at the greatest risk for serious complications.

The infection spreads through respiratory droplets when an infected person coughs or sneezes. The bacteria attach to the lining of the airways, release toxins, and cause inflammation that leads to the hallmark coughing spells. The disease typically follows three stages: the catarrhal stage (mild cold‑like symptoms), the paroxysmal stage (intense coughing fits), and the convalescent stage (gradual recovery).

Common Causes

Although the primary cause of pertussis is the bacterium Bordetella pertussis, several factors increase the likelihood of infection or mimic its presentation. Below are the most frequently associated conditions and risk factors.

• Bordetella pertussis infection – the classic bacterial cause.
• Bordetella parapertussis – a related bacterium that can produce a milder cough illness.
• Incomplete vaccination – children who miss or delay the DTaP series are more vulnerable.
• Waning immunity – immunity from childhood vaccination or natural infection declines after 5–10 years.
• Close contact with infected individuals – households, schools, and daycare centers are high‑risk settings.
• Smoking exposure – tobacco smoke damages airway cilia, making colonization easier.
• Premature birth or low birth weight – infants have less mature immune systems.
• Underlying lung disease – asthma, chronic obstructive pulmonary disease (COPD), or cystic fibrosis increase susceptibility.
• Immunocompromised states – HIV, chemotherapy, or long‑term corticosteroids.
• Travel to regions with low vaccination coverage – increases encounter with circulating pertussis strains.

Associated Symptoms

Symptoms evolve as the infection progresses.

• Catarrhal stage (1‑2 weeks): Runny nose, low‑grade fever, mild sore throat, and occasional dry cough.
• Paroxysmal stage (2‑6 weeks, may last up to 10 weeks):
  • Severe coughing fits lasting several minutes.
  • Inspiratory “whoop” sound (more common in children than adults).
  • Post‑tussive vomiting.
  • Facial flushing or bluish lips due to reduced oxygen.
  • Exhaustion after coughing episodes.
• Convalescent stage (weeks to months): Cough becomes less frequent but may persist for months, especially after exposure to cold air or respiratory irritants.
• Other possible findings:
  • Low‑grade fever.
  • Runny or stuffy nose.
  • Stridor or noisy breathing (especially in infants).

When to See a Doctor

Because pertussis can become severe, especially in babies, early medical evaluation is crucial. Seek care promptly if you notice any of the following:

• Prolonged coughing spells lasting >2 weeks, especially if they end in a whoop.
• Vomiting after a cough.
• Difficulty breathing, chest retractions, or noisy breathing.
• Bleeding from the nose or mouth after coughing.
• Fever higher than 101°F (38.3°C) that does not improve with over‑the‑counter medications.
• Signs of dehydration (dry mouth, reduced urine output, dizziness).
• Any infant younger than 3 months with a cough, apnea episodes, or poor feeding.
• Pregnant women or individuals with compromised immune systems experiencing cough.

Early treatment shortens the contagious period and reduces the risk of complications.

Diagnosis

Physicians combine clinical judgment with laboratory testing.

Clinical Evaluation

• Detailed history (vaccination status, exposure to known cases, symptom timeline).
• Physical exam focusing on respiratory sounds, oxygen saturation, and signs of distress.

Laboratory Tests

• Nasopharyngeal swab for PCR – the most sensitive test, detecting bacterial DNA within the first 3 weeks of illness.
• Culture – gold standard but less sensitive; results take up to 7 days.
• Serology – measurement of pertussis‑specific IgG antibodies; useful after the first 2 weeks when PCR may be negative.

Additional Tests (if complications are suspected)

• Chest X‑ray – to rule out pneumonia.
• Complete blood count – may show lymphocytosis, a classic but non‑specific finding.
• Pulse oximetry – to monitor oxygen levels in severe cases.

Treatment Options

Treatment aims to eradicate the bacteria, reduce symptom severity, limit contagion, and prevent complications.

Antibiotic Therapy

• Macrolides (first‑line):
  • Azithromycin 10 mg/kg on day 1, then 5 mg/kg daily for 4 days (total 5‑day course).
  • Erythromycin 40‑50 mg/kg/day divided every 6 hours for 14 days (taste‑related GI side effects are common).
  • Clarithromycin 15 mg/kg/day divided twice daily for 7 days.
• Trimethoprim‑sulfamethoxazole (TMP‑SMX) – alternative for macrolide‑resistant strains.
• Antibiotics are most effective when started within the first 3 weeks of cough onset; they may still be given later to prevent spread to contacts.

Supportive Care

• Maintain hydration – offer small, frequent fluids.
• Humidified air or a cool‑mist vaporizer to ease airway irritation.
• Position infants on their side during coughing spells to reduce aspiration risk.
• Limit exposure to smoke, strong odors, and allergens.
• For severe coughing episodes, a healthcare provider may prescribe a brief course of a bronchodilator or a low‑dose corticosteroid, though evidence is limited.

Hospital Management (for severe cases)

• Monitoring of oxygen saturation and respiratory effort.
• Intravenous fluids for dehydration.
• Pulse‑oximetry and, if needed, supplemental oxygen or mechanical ventilation.
• Isolation precautions (droplet precautions) until 5 days of appropriate antibiotics have been completed.

Prevention Tips

Vaccination is the cornerstone of pertussis prevention.

• DTaP vaccine for infants and children (5 doses at 2, 4, 6, 15‑18 months, and 4‑6 years).
• Tdap booster for adolescents (11‑12 years), adults, and pregnant women (preferably between 27‑36 weeks gestation each pregnancy).
• Adults who have close contact with infants < 12 months should receive a Tdap dose if not up‑to‑date.
• Practice good respiratory hygiene: cover coughs, wash hands regularly, and avoid close contact with sick individuals.
• Limit tobacco smoke exposure at home and in public places.
• Ensure timely prenatal care to receive the Tdap vaccine during pregnancy, which provides passive immunity to the newborn.

Emergency Warning Signs

References

• Mayo Clinic. Whooping cough (pertussis). https://www.mayoclinic.org/diseases-conditions/whooping-cough
• Centers for Disease Control and Prevention (CDC). Pertussis (Whooping Cough). https://www.cdc.gov/pertussis
• National Institute of Allergy and Infectious Diseases (NIAID). Bordetella pertussis. https://www.niaid.nih.gov/diseases-conditions/pertussis
• World Health Organization (WHO). Pertussis vaccines: WHO position paper. https://www.who.int/publications/i/item/WHO-PIP-2015.02
• Cleveland Clinic. Whooping cough (pertussis) – symptoms, treatment, and prevention. https://my.clevelandclinic.org/health/diseases/15716-whooping-cough
• American Academy of Pediatrics. Red Book: 2021–2024 Report of the Committee on Infectious Diseases.

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