MAJOR OUTBREAK OF PERTUSSIS IN NORTHERN ALBERTA, CANADA - ANALYSIS OFDISCREPANT DIRECT FLUORESCENT-ANTIBODY AND CULTURE RESULTS BY USING POLYMERASE CHAIN-REACTION METHODOLOGY

A major outbreak of 5,683 cases of pertussis occurred in northern Albe rta, Canada, from December 1989 to January 1991. The outbreak highligh ted a number of problems with current methods of pertussis diagnosis. In particular, an exceptionally high proportion of direct fluorescent- antibody (DFA)-positive, culture-negative specimens (88.4%) was identi fied. We took this opportunity to use polymerase chain reaction (PCR) methodology to examine whether the low culture rates were due to speci mens containing dead organisms or whether the DFA results represented high numbers of false-positive results. A set of primer sequences with in a Bordetella pertussis-specific repetitive element was used to ampl ify proteinase K extracts of B. pertussis DNA recovered from 279 submi tted slides inoculated at the point of collection with nasopharyngeal material obtained from pernasal swabs. The PCR data corroborated the c ulture results: 84.6% of DFA-positive, culture-negative specimens were similarly PCR negative. At least three different bacterial species th at were significantly cross-reactive with the commercial DFA reagent w ere identified in clinical specimens and in pure culture, providing on e possible explanation for the false-positive DFA results. These resul ts and other limitations of current diagnostic techniques underline th e urgent need for a new DFA reagent with improved specificity and a st andardized means of measuring the patient antibody response for the di agnosis of pertussis.