Rationale:

• Patients who have been raped may have fragments of the assailant's skin, blood, facial hair, or other foreign material from the rape site beneath their fingernails.
• The crime lab may be able to recover perpetrator DNA from body areas where the perpetrator deposited saliva, semen, or blood during the assault.
• Perpetrator pubic hairs found by combing the patient's pubic hair can often provide enough cellular DNA material from the root to enable the crime lab to do DNA analysis.
• If the patient had voluntary intercourse 48 hours before the sexual assault, examiners collect samples separately from both the vagina and the cervix because this may distinguish two separate male DNA patterns that can aid justice workers; sperm can survive much longer in cervical mucus than in the vagina.

Evidence:

• A 6-year review of crime lab specimens found that significant hair transfer after sexual assault occurs in less than 5% of cases (39).
• A large case series from a British forensic science laboratory of 2410 swabs found spermatozoa in oral smears up to 6 hours after the attack despite tooth brushing, using mouthwash, and drinking various fluids (40).
• Study of vaginal wet mount after voluntary coitus in 15 couples has shown a negligible chance of finding motile sperm from a vaginal wet mount more than 12 hours after intercourse (41).
• A prospective observational study of 178 consensual coital acts found that sperm can be recovered after intercourse from the cervix for up to 12 days and from the vagina for up to 9 days (42).

Comments:

• If a patient's clothing must be collected, the medical provider should assume responsibility of providing suitable dress for the patient to wear home after evaluation.
• Some localities request plucked public hairs. Although the routine pulling of the patient's hair from the roots may provide the best sample, the act of pulling the patient's hair may be considered insensitive and unnecessary during the initial evaluation. These hairs will rarely be needed because most cases do not concern this evidence, and DNA from the victim is most often obtained from blood or buccal cells. If needed, a patient can provide the hairs at a later time.
• In previous years some law enforcement agencies suggested collecting urethral swabs from male patients. Currently this practice is NOT recommended, as it fails to provide useful evidence and induces significant pain.