P38.06
Background: Nucleic acid amplification tests for the detection of C. trachomatis (CT) and N. gonorrhoeae (NG) in genital tract specimens has become the standard diagnostic method used in most laboratories for HIV prevention trials. The BD ProbeTec ET System, use Strand Displacement Amplification (SDA) technology for the direct, qualitative detection of CT and NG from DNA extracted from endocervical swabs, male urethral swabs, and urine specimens. The aim of this study is to compare two DNA extraction methods (M) (M1 as per package insert; M2 an international developed in house method) for the detection of CT and NG using the BDProbeTec ET instrument.
Methods: Our sample size included 60 vaginal swabs. The first set of extractions (method 1) was performed by conventional lysing, priming and amplification. The second method (2) included additional washing and centrifugation steps prior to lysis, priming and amplification. During the amplification process, external quality controls [College of American Pathologists: CAP] were included in the runs. As part of the validation process, samples were also processed at an external/reference laboratory.
Results: There was 100% concordance for CT/GC between the results obtained by the external/reference laboratory and MRC HPRU Central Laboratory using method 1, 100% sensitvity and specificity on GC/CT for all 60 swab samples. Method 2 achieved a 78% concordance; CT had 6 false negatives=70% sensitivity; 85% specificity; while GC had 4 false negatives=80% sensitivity; 90% specificity. CAP panels achieved 100% pass on both methods.
Conclusions: Method 1 as per package insert was superior to method 2 achieving a higher sensitivity and specificity. It is vital in populations with high HIV risk with co-infections with CT and NG that methods used for detection are accurate, specific and in keeping with the package insert which this study illustrates.
