Highlights
- •A survey about DNA contaminations in Switzerland.
- •About 1% of the profile sent to the national database are known to be contaminated.
- •Staff index elimination database allow early detection of contaminations.
- •Most contaminations likely occurred during DNA collection on crime scene.
- •Contamination prevention recommendations are necessary.
Abstract
In Switzerland, the DNA profiles of police officers collecting crime scene traces
as well as forensic genetic laboratories employees are stored in the staff index of
the national DNA database to detect potential contaminations. Our study aimed at making
a national inventory of contaminations to better understand their origin and to make
recommendations in order to decrease their occurrence. For this purpose, a retrospective
questionnaire was sent to both police services and forensic genetic laboratories for
each case where there was a contamination.
Between 2011 and 2015, a total of 709 contaminations were detected. This represents
a mean of 11.5 (9.6–13.4) contaminations per year per 1′000 profiles sent to the Swiss
DNA database. Feedbacks were obtained from the police, the laboratory or both for
552/709 (78%) of the contaminations. Approximately 86% of these contaminations originated
from police officers whereas only 11% were from genetic laboratories employees and
3% were associated to other sources (e.g. positive controls, stain–stain contaminations).
Interestingly, a direct contact between the stain and the contaminant person occurred
in only 51% of the laboratory contaminations whereas this number increased to 91%
for police collaborators. The high level of indirect DNA transfer in laboratories
might be explained by the presence of “DNA reservoirs” suggesting that cleaning procedures
should be improved. At the police level, most contaminations originated from the person
who collected the trace and likely occurred directly at the crime scene. Improving
sampling practices could be beneficial to reduce these contaminations.
Keywords
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Article info
Publication history
Published online: December 19, 2017
Accepted:
December 19,
2017
Received in revised form:
November 16,
2017
Received:
August 21,
2017
Identification
Copyright
© 2017 Elsevier B.V. All rights reserved.
