Post-coital vaginal sampling with nylon flocked swabs improves DNA typing

Area of Science:

• Forensic Science
• Genetics
• Sexual Assault Investigation

Background:

• Differential DNA extraction is standard for sexual assault cases.
• Low male-to-female DNA ratios in vaginal samples complicate analysis.
• Limited sperm cells and excess female cells create unfavorable DNA profiles.

Purpose of the Study:

• Compare standard cotton and nylon flocked swabs for post-coital vaginal sampling.
• Evaluate swab efficiency for microscopic, presumptive, and DNA typing analyses.
• Determine optimal swab type for forensic sexual assault investigations.

Main Methods:

• Collected 88 vaginal swabs (44 cotton, 44 nylon flocked) from 12 couples up to 84 hours post-intercourse.
• Performed microscopic examination for male cells.
• Conducted presumptive tests (RSID-semen, PSA) for seminal fluid.
• Performed DNA typing (STR profiles).

Main Results:

• Nylon flocked swabs showed 6-fold higher cellular elution efficiency.
• Microscopic analysis was faster with nylon swabs due to higher cell yield and better morphology.
• Presumptive tests were positive up to 60 hours; male DNA profiles up to 72 hours.
• Over 50% of presumptive-negative samples yielded informative male STR profiles.
• Nylon swabs yielded more male DNA after differential extraction.

Conclusions:

• Nylon flocked swabs enhance microscopic analysis in sexual assault cases.
• Nylon swabs improve male DNA isolation and typing success.
• The use of nylon flocked swabs is recommended for vaginal sampling in forensic investigations.