Q&A

Q: If a person received a Tdap vaccine and then had a positive pertussis PCR two weeks later, could it be a false positive from the vaccine, or should we consider this a case of pertussis? The patient had a cough, nausea and vomiting for two to three days prior to PCR testing.

A: Recent Tdap vaccination does not affect PCR testing. PCR tests are used to detect DNA sequences of the Bordetella pertussis bacterium. PCR tests are very sensitive and could give a false positive result for other reasons. For more information on the interpretation of pertussis diagnostic tests, see
www.cdc.gov/pertussis/clinical/diagnostic-testing/diagnosis-confirmation.html.