Most measures of male condom failure are indirect: studies have assessed self-reported rates of condom failure, unintended pregnancies, or transmission of sexually transmitted diseases among couples who consistently use condoms. To directly measure biological exposure to semen as a result of condom failure, VIDD member Dr. Ann Duerr, when working at the Centers for Disease Control and Prevention, and colleagues performed a study on 77 women who used condoms with their partners. They asked the women to self-report condom breaks and slips, and to collect post-coital vaginal swabs. These were later tested for presence of prostate-specific antigen (PSA, a protein found in semen) to determine biological exposure. The scientists found that women reported condom breaks or slippage nearly 8 percent of the time, a higher percentage than had been previously estimated for condom failure, but PSA was detected only 3.5 percent of the time. Women who reported taking measures to correct for condom failure, such as stopping intercourse or adjusting slipped condoms, had a lower chance of PSA being present.
Duerr A, Gallo MF, Warner L, Jamieson DJ, Kulczycki A, Macaluso M. Assessing Male Condom Failure and Incorrect Use. Sex Transm Dis. 2011 Jan 27.