PATHCHAT Edition No. 50
December 2018
Please contact your local Ampath pathologist for more information.
Authors: Dr. Kathy-Anne Strydom (Clinical Microbiologist) & Dr. Marcelle Myburgh (Clinical Virologist)
Introduction
✅ What is Pertussis?
- Pertussis (whooping cough) is a highly infectious respiratory disease caused by Bordetella pertussis.
- Other Bordetella species (B. parapertussis, B. holmesii) may cause milder forms of the disease.
✅ Transmission & Infectious Period:
- Spread via respiratory droplets.
- High secondary attack rate (up to 90%) in susceptible contacts.
- Incubation period: 5–21 days (average: 7–10 days).
- Most infectious during the early (catarrhal) phase but can transmit for up to 3 weeks if untreated.
📌 Despite high vaccine coverage, pertussis outbreaks occur in epidemic cycles every 2–5 years.
Epidemiology
🔹 Global & Local Trends:
- Pertussis is endemic worldwide.
- Recent resurgence despite vaccination efforts.
- South Africa has seen increased cases, especially in infants under 6 months.
- Growing incidence in adolescents and adults.
📌 Neonates and young infants have the highest morbidity and mortality from pertussis.
Clinical Presentation
✅ Classic Pertussis Stages (Most Common in Unvaccinated Children):
✔ 1. Catarrhal Stage (1–2 weeks):
- Nonspecific symptoms (cough, coryza, sneezing).
- Most infectious stage.
✔ 2. Paroxysmal Stage (2–8 weeks):
- Severe paroxysmal coughing fits.
- Inspiratory "whoop" after coughing spells.
- Post-tussive vomiting.
- Highest risk of complications (e.g., pneumonia, encephalopathy, seizures).
✔ 3. Convalescent Stage (1–2 weeks):
- Cough gradually resolves.
✅ Atypical Presentations:
- Neonates may present with apnoea, seizures, or pneumonia instead of classic cough.
- Vaccinated individuals and adults may have only a prolonged cough (no whooping).
📌 Atypical presentations delay diagnosis, increasing transmission risk and mortality.
Diagnosis of Bordetella Pertussis
✅ Diagnostic Methods:
- Polymerase Chain Reaction (PCR) (Preferred).
- Serology (Anti-pertussis toxin IgG).
- Culture (Not routinely performed).
🔹 Comparison of Diagnostic Methods:
✔ PCR Testing (Most Sensitive, Rapid Result):
- Sensitivity: 70–99%
- Specificity: 86–100%
- Specimen: Nasopharyngeal swab/aspirate or sputum
- Best performed in the catarrhal or early paroxysmal stage (before antibiotics).
- Single-copy gene targets have lower sensitivity but higher specificity than multi-copy targets.
✔ Serology (Useful for Late Presentations):
- Sensitivity: 50–99%
- Specificity: >90%
- Specimen: Blood
- Requires paired serum samples (acute and convalescent phases).
- Affected by recent vaccination or maternal antibodies in neonates.
✔ Culture (Not Routinely Used):
- Sensitivity: 12–60%
- Specificity: 100%
- Specimen: Nasopharyngeal swab/aspirate or sputum
- Requires specialized transport media for viability.
📌 Negative PCR does NOT rule out pertussis—results should be correlated with clinical suspicion.
Treatment of Pertussis
✅ Management is Primarily Supportive:
- Monitor for respiratory distress, especially in infants.
- Adequate hydration & nutrition support.
- Hospitalization for high-risk infants (age <3 months, severe disease, apnoea).
🔹 Antibiotic Therapy (Reduces Transmission, Not Disease Course):
✔ First-Line (Macrolides):
- Azithromycin (preferred in infants <1 month).
- Clarithromycin or erythromycin.
✔ Alternative:
- Trimethoprim-sulfamethoxazole (if macrolides are contraindicated).
📌 Antibiotics are most effective if given within 2 weeks of symptom onset.
Prevention of Pertussis
✅ Primary Prevention: Vaccination
- Acellular pertussis (aP) vaccine is part of the South African Expanded Programme on Immunisation (EPI).
- Immunity wanes after ~5 years, requiring booster doses.
🔹 Recommended Booster Schedule:
- Every 4–6 years (Tdap or TdaP vaccine).
- During each pregnancy (27–36 weeks gestation), regardless of prior vaccination.
- Healthcare workers & household contacts of neonates should be vaccinated.
📌 Maternal vaccination provides passive immunity to newborns and reduces pertussis-related infant mortality.
Post-Exposure Prophylaxis (PEP) for Close Contacts
✅ Who Should Receive PEP?
- Household contacts and family members.
- Infants <2 months old.
- Infants <1 year if not fully vaccinated.
- Pregnant women in their third trimester.
- Healthcare workers and caregivers in contact with infants.
✅ PEP Regimen:
- Macrolides (same as treatment).
- Start within 21 days of index case symptom onset.
📌 PEP is essential to prevent transmission, especially in households with young infants.
Key Takeaways for Clinicians
✅ Pertussis is highly contagious and remains a global health concern despite vaccination efforts.
✅ PCR is the preferred diagnostic test due to high sensitivity and rapid turnaround time.
✅ Atypical presentations occur in neonates, vaccinated individuals, and adults, often delaying diagnosis.
✅ Macrolides reduce transmission but have limited impact on disease course.
✅ Booster vaccinations are essential, especially in pregnant women and high-risk contacts.
✅ Post-exposure prophylaxis should be given to close contacts, particularly infants and pregnant women.
📌 Early recognition and prevention strategies are crucial to controlling pertussis outbreaks.