A comparison of the efficacy of different swab types in the absorption and elution of spermatozoa
Field, Jennifer Cochrane
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Swabs are an integral part of any forensic science “toolkit”. They can be used to gather many types of evidence at crime scenes, in the lab, or even in the hospital or morgue. Cotton swabs have been the traditional choice for most forensic laboratories, and for sexual assault kits. They have been the obvious choice for decades as cotton swabs were really the only option and they were and still are relatively inexpensive and easy to obtain. In the past dozen years or so, new synthetic fibers have been incorporated into novel swab designs. Fiber swabs can be made of polyester or rayon, polyurethane foam swabs can be round, narrow, oval or arrow shaped; swabs can also be flocked, or sprayed with strands of material such as nylon. The effectiveness of any type of swab used to collect biological material is based on three characteristics: the ability to pick up the material for which they are designed, the ability to hold that material until processed and then the ability to release as much of that material as possible to be analyzed in the lab. In this study, the efficacy of four different commercially available swabs to collect, store and release spermatozoa was evaluated. Puritan Cotton fiber swabs, Fisher Polyester fiber swabs, Fisher polyurethane swabs, and Copan nylon flocked swabs were all compared for their ability to pick-up and elute cells from solid surfaces. The surfaces included three types of commonly found tile: a smooth glossy ceramic tile, a rough non-porous ceramic tile, and a smooth semi-porous quarry tile. In general, polyester fiber swabs outperformed both the polyurethane foam and the nylon flocked swab when used on all three surfaces (P < 0.05). Polyester swabs were not significantly different from the cotton fiber swabs even though the average number of cells picked-up and eluted was higher overall. Swabs used to collect postcoital samples were also compared. Volunteer couples were given a variety of swabs to use after intercourse. The result of the comparison for the same four swab types when used as postcoital swabs was different from the results of the tile study. After estimating the number of cells collected and released from each swab, a comparison was made within each couple. Nylon flocked swabs yielded the highest level of cellular material overall and foam swabs recovered the least. This study demonstrates the need for further research into different swab types and in what capacities they are to be used in forensic science.