Pertussis diagnostics: overview and impact of immunization.

In all vaccinated populations, infections with Bordetella pertussis and Bordetella parapertussis continue to cause infections in unvaccinated infants and children, as well as in adolescents and adults with waning immunity. Thus in patients with longer lasting coughs a diagnosis of pertussis should be entertained irrespective of their vaccination status. Due to the non-specific clinical symptoms, clinically suspected cases of pertussis must be verified by laboratory methods. Hyperleukocytosis may be helpful in diagnosis for young infants, but in most cases, nonspecific laboratory tests have no role in pertussis diagnosis. Specific laboratory tests include direct detection of the bacteria or their DNA by culture or PCR, whereas serology serves as an indirect method to diagnose pertussis in those patients who present late in the development of the disease. Serology results can be interpreted in relation to reference values for different populations, but serology is unable to distinguish between vaccination and infection.