Evaluation of Level of Agreement in Bordetella Species Identification in Three U.S. Laboratories during a Period of Increased Pertussis

Abstract

While PCR is the most common method used for detectingBordetella pertussisin the United States, most laboratories use insertion sequence481(IS481), which is not specific forB. pertussis; therefore, the relative contribution of otherBordetellaspecies is not understood. The objectives of this study were to evaluate the proportion of otherBordetellaspecies misidentified asB. pertussisduring a period of increased pertussis incidence, determine the level of agreement inBordetellaspecies detection between U.S. commercial laboratories and the CDC, and assess the relative diagnostic sensitivity of CDC's PCR assay when using a different PCR master mix. Specimens collected between May 2012 and May 2013 were tested at two U.S. commercial laboratories forB. pertussisandB. parapertussisdetection. Every fifth specimen positive for IS481and/or IS1001with cycle threshold (CT) values of ≤35 was sent to CDC for PCR testing that identifiesBordetellaspecies. Specimens with indeterminate or negative results in the CDC PCR were tested using an alternate PCR master mix. Of 755 specimens, there was agreement in species identification for 83.4% (n= 630). Of the specimens with different identifications (n= 125), 79.2% (n= 99) were identified as indeterminateB. pertussisat CDC. Overall, 0.66% (n= 5) of the specimens were identified asB. holmesiiorB. bronchisepticaat CDC. Of 115 specimens with indeterminate or negative results, 46.1% (n= 53) wereB. pertussispositive when tested by an alternate master mix, suggesting a possible increase in assay sensitivity. This study demonstrates good agreement between the two U.S. commercial laboratories and CDC and little misidentification ofBordetellaspecies during the 2012 U.S. epidemic.