Once the sample is processed, the samples are tested for the presence of various pathogenic viruses. In my placement laboratory this is usually done by using the real time fast PCR instrument. This is a quick and reliable method, generating results by the end of the day. However, since the principle of PCR is molecular amplification of nucleic acid, it has a disadvantage of getting contaminated quite easily. If a sample even gets slightly contaminated by a few virus particles or previously amplified material, at the end of the test the nucleic acid of that virus will be greatly amplified in number, thus it will give a false positive result. It is very important to be careful when transferring materials from one place to another (pipettes into the wells), as chances of contamination are high during this stage. In reviewing the test results, it is always wise to suspect a contamination whenever a low positive sample is located next to a high positive one in a well plate or a strip of tubes. The low positive sample should be re-extracted and retested separately, if necessary using manual extraction. The original extract can also be retested and compared to the new extract, to deduce the point where contamination occurs. …show more content…
CSF samples are really important in nature as they are quite difficult to obtain, thus they are always tested in duplicates. However, in this scenario the duplicates showed a negative result. This created doubt in my mind as the positive sample was located next to high positive HSV-2 sample. So there was a possibility that contamination had occurred. Thus, the CSF sample was re-extracted again using column method and run again. The result was negative, conforming the fact that contamination had occurred due to a high titre of virus present in the adjacent