The problem of DNA contamination in forensic case work—How to get rid of unwanted DNA?

Comparison between various DNA sterilization procedures applied in forensic analysis

Background

The advanced sensitive STR kits applied in forensic DNA typing techniques can cause challenging issues when evidence samples are contaminated with minute quantities of DNA from another source such as forensic analysts or crime scene examiners.

Results

In this study, laboratory air and surfaces, gloves, tools, and equipment were evaluated as potential sources of contaminating DNA. Different sterilization methods were tested for their ability to efficiently eliminate DNA in a sample. Inactivation methods included 10% bleach, ethanol, UV light, and DNA-ExitusPlus IF. Exposure to the different inactivation protocols for varying periods of time was performed in two lab settings: low template DNA and DNA database labs. Surfaces were swabbed and any adhering DNA was quantified using HID real-time PCR. Results were detected using HID Real-Time PCR Analysis Software v1.2 and GeneMapper ID-X Software v1.4.

Conclusions

It was concluded that most of the DNA decontamination methods are not suitable for highly sensitive and precision STR kits such as GlobalFiler PCR Amplification Kit. The most suitable tested method was using DNA-ExitusPlus IF with the incubation time increased from 10 to 15 min.

Evaluation of Different Cleaning Strategies for Removal of Contaminating DNA Molecules

Decontamination strategies and their efficiencies are crucial when performing routine forensic analysis, and many factors influence the choice of agent to use. In this study, the effects of ten different cleaning strategies were evaluated to compare their ability to remove contaminating DNA molecules. Cell-free DNA or blood was deposited on three surfaces (plastic, metal, and wood) and decontaminated with various treatments. The quantities of recovered DNA, obtained by swabbing the surfaces after cleaning using the different strategies, was analyzed by real-time PCR. Large differences in the DNA removal efficiencies were observed between different cleaning strategies, as well as between different surfaces. The most efficient cleaning strategies for cell-free DNA were the different sodium hypochlorite solutions and Trigene^®, for which a maximum of 0.3% DNA was recovered on all three surfaces. For blood, a maximum of 0.8% of the deposited DNA was recovered after using Virkon^® for decontamination. The recoveries after using these cleaning strategies correspond to DNA from only a few cells, out of 60 ng of cell-free DNA or thousands of deposited blood cells.

Leading-edge forensic DNA analyses and the necessity of including crime scene investigators, police officers and technicians in a DNA elimination database

In recent years, sophisticated technology has significantly increased the sensitivity and analytical power of genetic analyses so that very little starting material may now produce viable genetic profiles. This sensitivity however, has also increased the risk of detecting unknown genetic profiles assumed to be that of the perpetrator, yet originate from extraneous sources such as from crime scene workers. These contaminants may mislead investigations, keeping criminal cases active and unresolved for long spans of time. Voluntary submission of DNA samples from crime scene workers is fairly low, therefore we have created a promotional method for our staff elimination database that has resulted in a significant increase in voluntary samples since 2011. Our database enforces privacy safeguards and allows for optional anonymity to all staff members. We also offer information sessions at various police precincts to advise crime scene workers of the importance and success of our staff elimination database. This study, a pioneer in its field, has obtained 327 voluntary submissions from crime scene workers to date, of which 46 individual profiles (14%) have been matched to 58 criminal cases. By implementing our methods and respect for individual privacy, forensic laboratories everywhere may see similar growth and success in explaining unidentified genetic profiles in stagnate criminal cases.

Sexual assault consultations - from high risk to high reliability

The sexual assault consultation is a high-risk procedure with the potential for errors resulting in harm to both patients and staff. As such, it can be likened to practices in highrisk industries such as aviation and surgery. In contrast to these domains however, the focus on performance safety and Threat and Error Management has not been widely adopted. This is despite a growing recognition of the vulnerabilities of the investigative and prosecutorial stages of alleged sexual assaults. In the context of “high risk” sexual assault consultations, the notion of safety refers not only to the risk of patient morbidity and mortality, but also to physical, psychological and judicial outcomes that affect patients, staff, and the wider community. This article identifies the latent threats present in sexual assault consultations and suggests a conceptual framework for application of Threat and Error Management in this specialised area of medicine. This will enable practitioners to be better equipped to recognise the risks and improve the performance and safety of sexual assault consultation processes. In an era of growing medicolegal concerns regarding issues such as environmental safety and the potential for contamination of cases, focussing on education and safety culture components within the investigative systems will allow sexual assault consultation processes to progress towards a new level of organisational reliability.