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Chapter 62 : Serologic and Molecular Tools for Diagnosing Bordetella pertussis Infection
In the last decade, there has been a dramatic resurgence of pertussis, particularly in adolescents and adults, likely as the result of a waning of vaccine induced immunity. Detection of the etiologic agent is the optimal method of making a laboratory diagnosis; however, with Bordetella pertussis infections, the nature of the infection and the natural history of the infection make this difficult. Because of the difficulties with the test, DFA staining should only be used in conjunction with culture; some national surveillance systems do not accept DFA results as laboratory confirmation of pertussis infection. PCR is also less affected by antimicrobial effects than is cell culture, permitting laboratory diagnosis even after effective antibiotics have been initiated. The measurement of pertussis agglutinins is one of the oldest assays used for determining antibody titers against B. pertussis. Widely used in the early and mid-20th century, particularly in the Medical Research Council clinical trials that demonstrated the efficacy of whole-cell pertussis vaccines, pertussis agglutinins correlated well with population immunity to pertussis but did not predict individual protection. Pertussis toxin (PT) is the most important pertussis antigen and is responsible for many of the biological activities of B. pertussis. Proponents of the Chinese hamster ovary (CHO) cell neutralizing assay argue that the assay measures biologically active antibodies and thus might correlate better with protective antibodies. Improvements in serological diagnosis have the greatest potential for improving the laboratory diagnosis of pertussis, particularly as the epidemiology shifts from young infants and children to adolescents and adults.