This test is used to detect acute infection caused by the slow-growing, fastidious pathogen B. pertussis, the cause of pertussis or whooping cough. Nasopharyngeal specimens should be submitted for B. pertussis culture; aspirates are preferred. Anterior nares or throat specimens are unacceptable. Transport medium (e.g., Regan-Lowe) is recommended. Specimens are typically inoculated onto an enriched, selective agar, like Regan-Lowe.
Turnaround time: Most cultures are positive in 7 " “10 days, although some cultures are incubated for up to 14 days. Additional time is required for final identification and further characterization.
Interpretation
Expected results: Negative. A negative culture does not exclude the diagnosis of pertussis, especially when a specimen is collected after the early, acute phase of infection.
Positive results: Confirm the diagnosis of pertussis.
Limitations
The sensitivity of culture for B. pertussis falls significantly after the first 7 " “14 days after onset of symptoms. Poor specimen collection, submission of specimens other than nasopharyngeal specimens, and submission of specimens during the chronic phase of disease are associated with poor sensitivity of culture.
Other Considerations
PCR methods have been described for diagnosis of pertussis. Cross-reactions have been described (e.g., Bordetella holmesii) and may limit the utility of molecular diagnostic testing. The sensitivity of PCR is greatest in the early acute phase of infection, but B. pertussis DNA may be detectable for weeks after resolution of acute disease. A number of serologic assays are commercially available, including assays for IgM and IgA. Variable sensitivity and specificity have limited the clinical utility of these assays.