In light of the strict legal scrutiny surrounding DNA
typing at this time, it has become necessary to systematically address
the issue of PCR contamination. To precisely define the parameters
affecting PCR contamination under casework analysis
conditions, PCR amplification reactions were intentionally compromised
by employing sub-standard laboratory technique and by introducing
secondary sources of DNA.
The PCR parameters considered for potential sources of contamination
include amplification set-up, amplification product handling,
aerosol DNA and storage. In addition, analyst technique was
evaluated by modifying or eliminating standard safeguards.
Under the circumstances normally encountered during casework
analysis, PCR contamination was never noted. Significantly, using
the dot blot detection method, contamination was never observed
when nanogram quantities of genomic DNA were mishandled or
aerosolized. Contamination occurred only when amplification product
was carelessly manipulated or purposefully sprayed near or directly
into open tubes containing water or genomic DNA. Although
standard precautions should be employed during PCR-based DNA
typing, our data indicates that contamination during amplification
procedures is not prevalent when detected by dot blot analysis.