How useful is the pertussis IgA serology test?
This test has marginal sensitivity in children and infants. It may take 3-4 weeks to become positive in patients with symptomatic pertussis. Positive results obtained in the first 3 weeks of a cough illness should be regarded with caution- the result may be a false positive. In patients who present within 3 weeks of the onset of a pertussis-like illness, samples for PCR testing are to be greatly preferred.
