Positive impact of DNA contamination minimization procedures taken within the laboratory.

DNA contamination incidents are one of the most frequent sources of error in forensic genetics and can have serious consequences. It is therefore essential to take measures to prevent these events and to monitor the real impact of contamination minimization procedures. In this study, we review and compare the number of contamination events detected on trace samples analyzed by the Forensic Genetic Unit (FGU) of the University Center of Legal Medicine in Switzerland before and after the implementation of new contamination minimization procedures. Interestingly, the number of contamination events by laboratory staff was significantly reduced by more than 70% after the implementation of the procedures. However, no significant change was observed for contamination events by police collaborators. This difference is likely to be explained by the differential impact of procedures taken in the laboratory and on crime scene. It suggests that the reduction observed for laboratory contamination incidents is due to the new procedures taken. In conclusion, our study highlights that taking appropriate measures is efficient and can reduce the number of contamination incidents. However, it is important that such contamination minimization procedures be implemented all along the chain of analysis of a stain (i.e. from crime scene to the laboratory).