Qualitative assessment of pertussis diagnostics in United States laboratories.

BACKGROUND: United States national surveillance data show that the use of culture for pertussis diagnostics has sharply declined, whereas polymerase chain reaction (PCR) is now the most common testing method. PCR testing for pertussis is rapid and sensitive, but the lack of standardization and variable specificity is concerning.
METHODS: A web-based survey containing 12 questions was sent to public health, commercial and hospital-based US laboratories performing clinical diagnostics to determine the pertussis diagnostics used. An extensive real-time PCR (RT-PCR) questionnaire accompanied a proficiency panel assessing the types of extraction methods, RT-PCR methods and current quality control in place at the laboratories. The proficiency panel of 12 specimens containing Bordetella pertussis at various concentrations and negative controls was created to detect cross-contamination and assess the lower limit of detection.
RESULTS: One hundred twenty-three (35%) of 355 respondents from the web-based survey performed diagnostic tests for the presence of B. pertussis. Eighty-three (71%) labs reported performing culture, whereas 67 (54%) labs used PCR. All 41 laboratories that consented to participate in the proficiency exercise used the IS481 RT-PCR target; however, a variety of extraction and RT-PCR methods were employed. The laboratories correctly identified 92% of the B. pertussis specimens, and 5% of the laboratories (1.8% of the panel specimens) reported at least 1 false-positive.
CONCLUSIONS: The small percentage of false-positives suggests that adequate procedures are in place to prevent cross-contamination. Differing extraction and PCR methods as well as variable analytic sensitivity emphasize the necessity for an external well-defined quality control program and interlaboratory pertussis PCR harmonization.