DNA transfer: DNA acquired by gloves during casework examinations

As loss and/or contamination of DNA evidence can have major negative implications, it is incumbent on forensic practitioners to minimise this risk. DNA transfer during examination of items, even when wearing gloves, is a potential risk. Here we observe a number of laboratory based biological evidence recovery personnel performing a range of examinations to help evaluate the risks. Assessments are made of; what is touched by each glove and in which sequence; the number, duration and types of contacts made by each glove with the item under examination, tools used and any other surfaces; when the gloves are replaced; as well as DNA profiles of samples taken of the worn gloves at time of replacement against those relating to the item under examination, the examiner and other staff members. Observations show that many different surface areas are touched by gloves during examinations. Differences were observed among examiners in what they touched and when they changed gloves. DNA was retrieved from the outer surfaces of the majority of gloves examined. In many instances the case associated person of interest was observed within the profile generated. So too were profiles of the examiner or other staff members, predominantly from the first and last gloves used during the examination, which were associated with removing the exhibit from its packaging and repackaging it. Several of the observed contacts made by the gloves were deemed high contamination risk events. This study is one of the first to investigate DNA transfer during actual casework examinations, increases our awareness of potential DNA contamination risks during the examination of exhibits, and highlights the need to consider improvements in procedures and/or training of those involved with forensic examinations.