The Impact of Switching to Polymerase Chain Reaction for the Diagnosis of Chlamydia Trachomatis Infections in Women

Article excerpt

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(R) 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.

Chlamydia trachomatis is an important sexually transmitted disease. There is some evidence that an earlier decline in incidence has been replaced with a resurgence of infections. The decline had been attributed to a number of factors. There may be changing patterns of sexual activity among young adults, condom usage is more frequent, and more effective therapies are available.1,2 Probably one of the most important contributors to the decline in C. trachomatis infection was the increased availability of rapid and accurate diagnostic tests. Over the last two decades, testing has moved from tissue culture to direct immunofluorescence to enzyme immunoassay (EIA) and to molecular methods testing based on either the ligase or polymerase chain reactions (LCR and PCR).3 The sensitivity of these and other molecular based methods is significantly higher than that of previously employed methods.4-10

In the second half of 2001, we observed what appeared to be a significantly higher than normal number of cases of C. trachomatis infection in the Capital Health region of Nova Scotia. We wished to examine the impact of the switch on the proportion of specimens in which we detected C. trachomatis and to examine the cost implications.

MATERIALS AND METHOD

The Microbiology Laboratory of the Queen Elizabeth II Health Sciences Centre provides diagnostic microbiology services to the Capital Health region in the province of Nova Scotia. A small number of chlamydia EIA tests are also performed at the Izaak Walton Killam Health Centre (approximately 2,000 yearly). IWK testing was done primarily on children and women seeking gynecologic and obstetrical services at that hospital; all other testing was performed in our laboratory. Information on the number of EIA and PCR tests performed on women was retrieved from an abstracted laboratory information service database. We examined records of testing performed between April 1, 1998 and December 31, 2001.

Chlamydia trachomatis testing

Prior to June 2001, all genital swabs submitted for diagnosis of chlamydial infection were tested using the MicroTrak, II Chlamydia EIA (Behring Diagnostics Inc., Cuppertino, CA). Testing was performed on the Syva MicroTrak, II Autoreader (Behring Diagnostics Inc., Cuppertino, CA) in accordance with the manufacturer's instructions. All specimens with a reactive or grey zone EIA were confirmed by direct fluorescence examination of the centrifuged sediment of the residual specimen using the MicroTrak, II DFA reagents supplied by the manufacturer. …