Efforts toward optimization of sexual assault swab processing
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Citation
Abstract
One way to address the sexual assault kit (SAK) backlog in the United States is by improving the efficiency of SAK swab processing. Three areas which could benefit from optimization were addressed in this study. Swab elution time and number of centrifugations varies among forensic labs, therefore, precision in this step would reduce time spent performing these steps for longer than is necessary. If successful, staining spermatozoa pellets while in the tube, rather than on the microscope slide, would speed up the slide preparation process. Finally, using the same swab cutting tested for acid phosphatase (AP) during microscope slide preparation, immunoassay card testing, and deoxyribonucleic acid (DNA) analysis, would reduce the amount of consumed evidence and simplify the process.
Determination of ideal elution time and number of centrifugations was done by calculating the relative percentage of eluted spermatozoa after a first and second elution and comparing these values between four elution time categories. A procedure for in-tube spermatozoa staining was experimentally developed and evaluated by examination of microscope slides. Sets of experimental (exposed to AP Spot reagent) semen-only and semen-saliva swabs of various dilutions were compared to sets of control swabs by means of their microscope slides, immunoassay card test results and DNA profiles. Additionally, the quantities of DNA extracted from post-eluted swabs were compared to those from spermatozoa pellets.
An elution time of 30 minutes was found to be just as adequate as longer elution times, and a single centrifugation following elution was determined to be sufficient for spermatozoa detection. The in-tube spermatozoa staining method had a negative effect on the number of spermatozoa present on the microscope slides, therefore it was not incorporated into subsequent procedures. AP Spot reagent seemed to have no effect on swab processing and downstream testing, and the amount of DNA remaining on post-eluted swabs is significant; thus, swabs should be recombined with their cellular pellets prior to DNA analysis.