II. Technique: Obtaining Samples
-
Dacron Polyester swab of posterior nasopharynx
- Insert into posterior nostril
- Leave swab in place for 10 seconds
- Do not swab anterior nare or throat (low efficacy)
- Nasopharyngeal aspirate
- Higher efficacy than swab
- Requires special equipment
III. Labs: Tests Recommended by CDC (obtain both PCR and culture)
- Nasopharyngeal swab PCR (preferred first-line)
- Indicated as first-line test for Pertussis
- Sample obtained with nasopharyngeal Dacron or nylon swab with results back in 1-2 days
- Efficacy
- Sufficient accuracy alone (Pertussis Culture was previously recommended for confirmation)
- Test Sensitivity: 77 to 97%
- Much better Test Sensitivity than Pertussis Culture
- Test Sensitivity best in first 3-4 weeks (wanes after 4 weeks)
- Test Specificity: 88 to 97%
- False Negatives after 4 weeks of cough
- Lower Test Specificity than culture (higher False Positive Rate)
- Bordatella Pertussis Culture
- Indicated during Pertussis outbreaks and for strain identification
- Sample obtained with nasopharyngeal Dacron or nylon swab
- Requires special transport media and culture conditions
- Results are delayed 7-10 days
- Efficacy
- Test Specificity: 100%
- Test Sensitivity: 20 to 80%
- Low Test Sensitivity (approaches 80% only in first two weeks, then falls off towards 20%)
- False Negatives occur at >2 weeks from cough onset
- False Negatives also occur in those Pertussis vaccinated or on Antibiotics
- After Erythromycin for 4 days: Test Sensitivity approaches 0%
-
Pertussis
Serology
- Indicated in late presentation from onset of cough (4-12 weeks)
- However, results are not standardized - Exercise caution
- Efficacy
- Test Sensitivity: 65%
- Test Specificity: 92%
- False Positives in recently vaccinated patients (within last year)
- False Positives in infants age <6 months (maternal antibodies)
IV. Labs: Tests Not recommended by CDC
- Direct fluorescent Antibody assays
- Low Test Sensitivity and Test Specificity