A novel nested polymerase chain reaction targeting the testis-specific protein Y-encoded family of genes for high sensitivity of recent semen exposure detection: Comparison with four other assays of semen detection.

Objectives: Because self-report of sexual behaviours is prone to biases, biomarkers of recent semen exposure are increasingly used to assess unprotected sex. We aimed to present a novel nested polymerase chain reaction (PCR) assay targeting testis-specific protein Y-encoded (TSPY) genes and to compare its performance in detecting recent semen exposure with that of four other assays.

Methods: Forty-five vaginal samples were selected at baseline of a prospective observational demonstration study of early antiretroviral treatment and pre-exposure prophylaxis among female sex workers in Benin. Semen exposure was assessed with: a rapid prostate-specific antigen (PSA) detection assay, a quantitative PCR targeting the sex-determining region (SRY) gene, a standard PCR targeting SRY, a standard PCR targeting TSPY, and a nested PCR targeting TSPY (n-TSPY). Because we had hypothesized that n-TSPY would be the most sensitive of the five assays while remaining specific, and as our results suggested that it was the case, sensitivity and specificity were calculated for each assay in comparison with n-TSPY.

Results: The n-TSPY could detect male DNA at concentration 16 and 64 times lower compared to s-TSPY and s-SRY, respectively. Among the 45 vaginal samples, prevalences of semen exposure according to the different assays varied from 22.2% (95%CI: 11.2%-37.1%) to 70.5% (95%CI: 54.8%-83.2%), with the highest prevalence measured with n-TSPY. The n-TSPY products were of expected size and we observed no false-positive in female DNA controls. The assay that offered the second best performance in detecting semen exposure was the PSA rapid test, with a sensitivity of 61.3% and a specificity of 100% compared to n-TSPY.

Conclusions: Compared to n-TSPY, all other PCR assays had poor performance to detect semen exposure. The n-TSPY is an accessible assay that may have great utility in assessing semen exposure in studies where many factors are expected to accelerate biomarkers' clearance.