Bordetella pertussis Antibody Test
🦠 Bordetella pertussis Antibody Test: Complete Guide
A key serologic test for pertussis diagnosis, immunity assessment, and post-vaccination evaluation
1. What Is Bordetella pertussis?
Bordetella pertussis is the causative bacterium of pertussis (whooping cough), a respiratory infection affecting both children and adults.
Key Characteristics
- Gram-negative, small respiratory pathogen
- Human-exclusive infection, transmitted via droplets
- Attaches to ciliated epithelial cells → produces toxins → induces paroxysmal cough
- Major virulence factors: Pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN)
- Vaccine-preventable, though immunity wanes over time
2. What Is the Bordetella pertussis Antibody Test?
This test measures IgG antibodies against pertussis antigens (primarily PT) to assess evidence of infection or immunity.
3. Indications
✔ 1) Diagnosis of Pertussis Infection
- When PCR is negative or inconclusive
- For patients with persistent cough lasting >2–3 weeks
✔ 2) Evaluation of Vaccine-Induced Immunity
- Assess serologic response after dTap/Tdap vaccination
- Useful for healthcare workers, pregnant women, and high-risk groups
✔ 3) Epidemiologic Surveillance
- Outbreak investigation
- Population-based immunity studies
4. Test Method: EIA / ELISA
The EIA (ELISA) method is the most widely used.
Principle
- Microplate coated with PT (or FHA, PRN) antigens
- Patient serum added → antigen–antibody binding
- Enzyme-linked secondary antibody reacts with substrate
- Optical density (OD) measured
- IgG levels quantified in EU/mL
Advantages
- High sensitivity and specificity
- Automated and standardized
- Useful even when PCR becomes negative in later stages
5. Reference Ranges
Ranges vary by manufacturer, but typical cutoffs include:
- PT-IgG < 10 EU/mL
- FHA-IgG < 10 EU/mL
6. Clinical Interpretation
✔ 1) Elevated IgG (Positive Result)
Indicates:
- Recent pertussis infection or
- Vaccine-induced immunity
PT-IgG is the most specific marker for true pertussis infection.
Post-vaccination antibody levels typically rise within 2–3 weeks.
✔ 2) Low or Negative IgG
- No detectable immunity
- Waning immunity years after infection or vaccination
- Helpful for determining need for booster vaccination
7. Important Considerations
🔸 1) Positive IgG ≠ Acute Infection
- Antibodies can persist for years
- Vaccination also elevates IgG
➡ Must interpret with clinical symptoms and PCR results
🔸 2) PT-IgG Is the Most Specific
- FHA and PRN antibodies may cross-react with other Bordetella species or non-specific antigens
🔸 3) PCR Remains the Preferred Acute Test
- Antibodies may not appear in the first 2 weeks
- Early disease → PCR sensitivity highest
🔸 4) Special Populations
- Pregnant women and healthcare workers: verify Tdap status
- Pertussis poses severe risk in young infants
8. Interpretation Summary
| Result | Interpretation |
|---|---|
| IgG +, PCR – | Prior infection or prior vaccination likely |
| IgG +, PCR + | Strong evidence of current infection |
| IgG –, PCR + | Early infection (antibodies not yet formed) |
| IgG –, PCR – | Low probability of pertussis (check symptoms) |
9. Key Takeaways
- Pertussis IgG testing is crucial for diagnosis, immunity assessment, and post-vaccination evaluation
- ELISA-based PT-IgG quantification is the standard
- Elevated IgG indicates recent infection or vaccination
- Always interpret results with PCR and clinical findings to avoid misdiagnosis
📚 References
- CDC. Pertussis (Whooping Cough): Laboratory Testing Guidelines
- UpToDate: Diagnosis of Bordetella pertussis infection
- WHO: Pertussis Laboratory Manual
- Cherry JD. Pertussis in adults. Ann Intern Med
- Tietz Textbook of Clinical Chemistry