Laboratory method | Reported sensitivity* | Reported specificity* | Comments |
Culture of nasopharyngeal secretions | 20 to 80 percent (decreases with increasing duration of cough) | 100 percent | - Traditional reference standard for diagnosis.
- Sensitivity depends on duration of symptoms and decreases after two weeks of illness; prior vaccination or antibiotic exposure also decrease sensitivity.
- Permits antibiotic susceptibility testing and strain serotyping (helpful in outbreak setting).
- Results available in three to seven days.
- Not available in all laboratories.
- In an outbreak setting, confirmation is recommended for at least one case of suspected pertussis.
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Polymerase chain reaction of nasopharyngeal secretions¶ | 61 to 94 percent | 88 to 98 percent | - Rapidly available results.
- More sensitive than culture, but sensitivity decreases after three weeks of illness.
- No standard methodology.
- Subject to contamination, especially during outbreaks.
- May also be positive in Bordetella holmesii and Bordetella bronchiseptica.
- May detect nonviable Bordetella pertussis organisms.
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Serology (ELISA) blood | 60 to 95 percent | Δ | - A CDC/FDA-developed assay has been useful in outbreak settings; the accuracy of commercially available assays is not known.
- In general, serology is most useful for diagnosis two to eight weeks after cough onset. A single high antibody titer above a designated threshold may be sufficient and obviate the need for acute/convalescent titers; this cutoff is often laboratory specific.
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