Differences in the sensitivity of the Amplicor Chlamydia trachomatis PCR assay

Use of pooled urine samples and automated DNA isolation to achieve improved sensitivity and cost-effectiveness of large-scale testing for Chlamydia trachomatis in pregnant women

The success of large-scale screening for Chlamydia trachomatis depends on the availability of noninvasive samples, low costs, and high-quality testing. To evaluate C. trachomatis testing with pregnant women, first-void urine specimens from 750 consecutive asymptomatic pregnant women from the Rotterdam area (The Netherlands) were collected. Initially, we investigated the performance of three different DNA isolation methods with 350 of these urines and 70 pools of 5 of the same subset of urine samples. The routinely used COBAS AMPLICOR test was compared to the COBAS AMPLICOR test with prior DNA isolation by use of the MagNA Pure large-volume kit and the MagNA Pure bacterial DNA isolation kit. The latter combination provided the best DNA test for pooled urines, with a sensitivity twice that of the other methods. Next, using all 750 urines, the COBAS AMPLICOR performance for individual testing was compared to pooled testing with the standard COBAS AMPLICOR procedure and subsequently to pooled testing with COBAS AMPLICOR in combination with the MagNA Pure bacterial DNA isolation kit. The sensitivity of COBAS AMPLICOR was 65% on individual and 42% on pooled urines but improved to 92% on pooled urines with the MagNA Pure bacterial DNA isolation kit, making this combination the best screening method. The C. trachomatis prevalence in this population appeared to be 6.4%. Additionally, the cost of the combined MagNA Pure bacterial DNA isolation kit and COBAS AMPLICOR method on pooled urines was only 56% of the cost of the standard COBAS AMPLICOR test applied to individual urines. Costs per positive case detected in the combined method were 39% of standard costs.