Abstract
Background: We noted a marked increase in Chlamydia trachomatis (CT) infections in the Capital Health Region of NS coincident with substitution of a PCR for an enzyme immunoassay (EIA). We reviewed our experience to determine the cost of switching and the impact on the number of new infections diagnosed.
Methods: Information on the number of EIA and PCR tests performed on women was retrieved from an abstracted laboratory information database. We examined records of testing performed between April 1998 and December 2001. Prior to June 2001, all genital swabs were tested using the MicroTrak‚ II Chlamydia EIA and confirmed by direct fluorescence examination. After July 2001, genital swabs were tested using the COBAS AMPLICOR® C. trachomatis test.
Results: During the study period, 62,288 EIA tests were performed on specimens submitted; 2,061 (3.33%) were positive. In the six months when testing was performed by the PCR method, 9,559 PCR tests were performed, 463 (4.84%) were positive; 46% increase. In the three years before PCR testing was implemented, an average of 1,626 specimens were submitted monthly. An average of 54 tests were positive (3.3%). The cost for each positive detected by PCR was $208 Cdn and $226 by EIA.
Conclusions: The switch to PCR for the diagnosis of CT produced a marked increase in the number of chlamydia infections diagnosed. The recent increase in the number of reported CT cases in Canada may be due in large part to more sensitive tests. Surprisingly, the cost of each positive test by PCR was $18 Cdn less than that of the EIA.
Résumé
Contexte: Il y a eu une augmentation marquée des infections à Chlamydia trachomatis (CT) dans la région sanitaire de la capitale de la Nouvelle-Écosse, qui coïncidait avec l’utilisation de l’amplification par la polymérase (PCR) en remplacement des essais immunoenzymatiques (EIA). Nous avons fait le bilan de l’expérience afin de déterminer le coût du changement et ses incidences sur le nombre de nouveaux cas d’infection diagnostiqués.
Méthode: Les données sur le nombre d’essais EIA et PCR effectués sur des femmes proviennent d’une base de données de laboratoire résumées. Nous avons examiné les dossiers des essais effectués entre avril 1998 et décembre 2001. Avant juin 2001, tous les prélèvements génitaux étaient testés par EIA (MicroTrak II Chlamydia) et confirmés au moyen d’un examen direct par fluorescence. Après juillet 2001, les prélèvements génitaux ont subi le test de dépistage de la C. trachomatis COBAS AMPLICOR®.
Résultats: Durant la période à l’étude, 62 288 EIA ont été effectués sur les prélèvements soumis; 2 061 (3,33 %) étaient positifs. Au cours des six mois où l’on a eu recours à la méthode PCR, 9 559 essais ont été effectués, dont 463 (4,84 %) étaient positifs, soit une hausse de 46 %. Les trois années précédant la mise en œuvre des essais PCR, on soumettait en moyenne 1 626 prélèvements par mois, et 54 essais en moyenne étaient positifs (3,3 %). Le coût unitaire des essais PCR positifs était de 208 $CAN (contre 226 $ pour les EIA positifs).
Conclusions: L’adoption de la méthode PCR pour le diagnostic de la CT a entraîné une hausse marquée du nombre d’infections à Chlamydia diagnostiquées. La hausse récente du nombre de cas de CT signalés au Canada pourrait s’expliquer en grande partie par la sensibilité accrue des tests. Curieusement, le coût unitaire des essais PCR positifs était inférieur de 18 $CAN à celui des EIA.
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