Comparison of Three Assays for Detection of Chlamydia trachomatis and Neisseria gonorrhoeae in SurePath Pap Samples and the Role of Pre- and Postcytology Testing
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ABSTRACTChlamydia trachomatis
and
Neisseria gonorrhoeae
are common causes of sexually transmitted infections, and there is interest in screening SurePath liquid-based Pap (L-Pap) samples with Aptima Combo 2 (AC2), Amplicor (AMP), and ProbeTec ET (PT) assays. SurePath L-Pap samples and a cervical swab (CS) were collected from 394 women attending health clinics in Hamilton and Toronto, ON, Canada. L-Pap samples were tested with the three assays prior to being processed for cytology, and the CS sample was tested with AC2. The prevalence of
C. trachomatis
was 8.9%, and that of
N. gonorrhoeae
was 1.5%. By using the positives from CS testing, as well as CS negatives corresponding to L-Pap samples that tested positive in 2 of 3 assays, the sensitivities of AC2, AMP, and PT for
C. trachomatis
in precytology samples were calculated to be 97.1% (34 of 35 positive samples were detected), 91.4% (32 of 35 were detected), and 77.1% (27 of 35 were detected), respectively. Six women were infected with
N. gonorrhoeae
. After cytology processing, the results of testing the remaining liquid in the L-Pap vial and the cell-enriched fraction for
C. trachomatis
by AC2 showed positive agreements of 98.9% (kappa [
k
], 0.93) and 98.7% (
k
, 0.92), respectively, with the results of testing precytology L-Pap samples. Although all testing showed high specificity, testing for
C. trachomatis
by AC2 was significantly more sensitive than testing by PT for SurePath samples (
P
= 0.02). Newer versions of AMP (Cobas 4800) and PT (Q
x
with XTR technology) need published evaluations for detecting
C. trachomatis
and
N. gonorrhoeae
in L-Pap samples.
C. trachomatis
testing can be performed with similar results on pre- and postcytology SurePath samples.
