Background Extra-genital infections are common in MSM and women and are frequently the sole sites of infection. However, analysing samples from the rectum and pharynx, in addition to the urogenital tract, trebles the diagnostic cost.
Aim Can samples from three sites be pooled into one NAAT container and still achieve the same sensitivity and specificity as the samples analysed separately?
Methods Women and MSM attending a sexual health clinic were invited into a ‘swab yourself’ trial. Two self-taken samples (one for separate analysis and one for pooling) were taken from the pharynx and rectum with VVS in women and FCU in MSM. The sampling order of the pooled or analysed separately swabs was randomised. Gonorrhoea (NG) and chlamydia (CT) were diagnosed using NAATs. Patient infected status was defined as at least two positive confirmed samples.
Results 1251 women and MSM were recruited to January 2016. Overall prevalence of infections was NG 5.7% and CT 17.8%. Sensitivity, specificity, PPV and NPV are shown in the table:
Conclusion This on-going study demonstrates that self-taken samples from the rectum, pharynx and urogenital tract are comparable in sensitivity and specificity if analysed separately or as a pooled sample. In MSM the diagnostic costs of three separate analyses are unaffordable for many health systems but a pooled sample has the same laboratory cost as a urogenital sample. These findings mean triple site testing could be expanded into women at no additional health service cost.
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