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Whooping Cough (Pertussis) in Infants

Overview

Whooping cough, medically known as pertussis, is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis. The disease is characterized by severe coughing fits that often end with a high‑pitched “whoop” sound when the infant breathes in.

Infants younger than 12 months are the most vulnerable group. In the United States, the Centers for Disease Control and Prevention (CDC) reported 12,394 pertussis cases in 2022, and about 50 % of those cases occurred in children under one year of age <sup>1</sup>. Worldwide, the World Health Organization estimates 24 million cases and 160,000 deaths annually, the majority of which are in infants <sup>2</sup>.

Because infants have immature immune systems and cannot complete the full pertussis vaccine series until at least six months of age, the infection can progress rapidly and become life‑threatening.

Symptoms

Pertussis in infants often presents differently than in older children or adults. The classic “whoop” is less common in babies; instead, they may show the following signs:

• Runny nose and mild fever – often the first signs, resembling a common cold.
• Persistent cough – starts as short, mild coughs, then progresses to long, violent coughing spells.
• Paroxysmal coughing episodes – sudden bursts of coughing that can last 1–2 minutes and occur many times a day.
• Inspiratory “whoop” – a high‑pitched gasp after a coughing fit; seen in only ~30 % of infants.
• Vomiting – due to intense coughing, especially after meals.
• Apnea – brief pauses in breathing during or after a coughing spell, more common in newborns.
• Chest retractions – the skin between ribs or under the breastbone pulls in tightly during a cough.
• Facial pallor or cyanosis – turning blue around the lips due to lack of oxygen.
• Difficulty feeding – coughing interferes with suck‑swallow‑breathe coordination.
• Lethargy or irritability – infant may be unusually sleepy or fussy.

Symptoms typically follow three stages:

1. Catarrhal stage (1–2 weeks) – cold‑like symptoms; most contagious.
2. Paroxysmal stage (1–6 weeks) – severe coughing bouts; whoop may appear.
3. Convalescent stage (2–4 weeks) – cough slowly improves but may persist for months.

Causes and Risk Factors

What causes whooping cough?

Pertussis is caused by the gram‑negative bacterium Bordetella pertussis. The organism attaches to the ciliated lining of the respiratory tract and releases toxins that:

• Impair ciliary function, preventing clearance of mucus.
• Cause inflammation and excessive mucus production.
• Induce the characteristic coughing spasms.

Who is at risk?

• Infants < 12 months – especially those < 3 months or not fully vaccinated.
• Unvaccinated or partially vaccinated children – vaccine coverage gaps increase community spread.
• Household contacts with pertussis – parents, siblings, grandparents.
• Pregnant women who are not up‑to‑date on tetanus‑diphtheria‑acellular pertussis (Tdap) vaccine.
• Individuals with weakened immune systems – e.g., premature infants, those on steroids.
• Settings with close contact – daycare centers, crowded homes.

Diagnosis

Early diagnosis is crucial because treatment is most effective within the first two weeks of symptom onset.

Clinical assessment

• Detailed history of cough duration, pattern, and exposure to ill contacts.
• Physical exam focusing on cough characteristics, presence of whoop, retractions, and signs of respiratory distress.

Laboratory tests

• Pertussis PCR (polymerase chain reaction) – detects bacterial DNA from a nasopharyngeal swab; most sensitive during the catarrhal and early paroxysmal stages.
• Culture – grows the organism on Bordet‑Gengou medium; gold standard but less sensitive and takes 5–7 days.
• Serology – measurement of IgG antibodies against pertussis toxin; useful after two weeks when PCR may be negative.
• Complete blood count (CBC) may show lymphocytosis, a classic but not universal finding.

Diagnostic criteria (CDC)

A confirmed case requires either a positive laboratory test (PCR, culture, or serology) or a clinically compatible illness with epidemiologic linkage to a confirmed case.

Treatment Options

Antibiotic therapy

Antibiotics do not cure the cough but reduce transmission and may lessen severity if started early.

• Azithromycin – 10 mg/kg once daily for 5 days (preferred for infants due to once‑daily dosing).
• Clarithromycin – 7.5 mg/kg twice daily for 7 days (alternative).
• Erythromycin – 40–50 mg/kg per day divided every 6 hours for 14 days (older regimen, more GI side‑effects).

Infants younger than 1 month may receive oral sulfamethoxazole‑trimethoprim if macrolide‑resistant strains are suspected, but this is rare.

Supportive care

• Hospitalization for infants with apnea, severe coughing, or inadequate feeding.
• Oxygen therapy to maintain oxygen saturation > 92 %.
• Bronchodilators – may be trialed but evidence of benefit is limited.
• Nasogastric feeding if the infant cannot take sufficient calories.
• Intravenous fluids for dehydration.

Adjunctive measures

• Frequent hand washing and use of masks by caregivers.
• Isolation of the infant until at least 5 days of appropriate antibiotics.
• Monitoring for secondary bacterial pneumonia (Chest X‑ray if fever > 38.5 °C persists).

Living with Whooping Cough in Infants

Even after the acute phase, coughing may linger for weeks. Practical tips for families include:

• Keep the infant upright during and after feeds to reduce cough‑triggered aspiration.
• Humidify the air – use a cool‑mist humidifier in the infant’s room to soothe irritated airways.
• Offer small, frequent feeds rather than large meals, which can provoke coughing.
• Monitor weight daily; a loss of > 10 % of birth weight warrants medical review.
• Limit exposure to smoke, strong fragrances, or other irritants.
• Schedule follow‑up appointments at 1‑week and 2‑week intervals to assess respiratory status.

Prevention

Vaccination

• Maternal Tdap vaccine – administered between 27–36 weeks gestation; provides passive antibodies to the newborn and reduces infant pertussis hospitalization by ~ 90 % <sup>3</sup>.
• Infant DTaP series – given at 2, 4, 6, and 15–18 months; on‑time completion is essential.
• Household “cocooning” – ensure all close contacts receive a Tdap booster (once, then every 10 years).

Other preventive measures

• Practice rigorous hand hygiene (wash hands with soap > 20 seconds).
• Avoid exposing infants to people with a persistent cough.
• Keep sick children home from daycare until they have completed at least 5 days of appropriate antibiotics.
• Use a clean, well‑ventilated environment; consider HEPA filters in homes with infants of high risk.

Complications

If untreated or inadequately managed, pertussis can lead to serious, sometimes fatal, complications in infants:

• Apnea and respiratory failure – most common cause of death in infants < 3 months.
• Pneumonia – bacterial superinfection of the lungs.
• Seizures – secondary to hypoxia during severe coughing spells.
• Encephalopathy – rare but possible, especially with prolonged hypoxia.
• Weight loss and failure to thrive due to poor feeding.
• Rib fractures – from intense coughing in older children (rare in infants).

When to Seek Emergency Care

References

1. Centers for Disease Control and Prevention. Pertussis (Whooping Cough) – CDC. Updated 2023.
2. World Health Organization. Pertussis Fact Sheet. 2022.
3. American College of Obstetricians and Gynecologists. Tdap Vaccination During Pregnancy. 2020.
4. Mayo Clinic. Whooping Cough — Symptoms and Causes. 2024.
5. Cleveland Clinic. Pertussis (Whooping Cough). Reviewed 2023.

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