I hope everyone now offering molecular testing for COVID outside of the routine laboratory network has all the appropriate checks in place to monitor for contamination. It’s a fact of life and something we check for regularly. Sometimes it’s not that easy to spot either #COVID19

Here’s a true story about contamination from an unusual source that I personally dealt with. I had a call from a clinician about a HSV-2 positive result on someone that had been tested as a screening tool because of discomfort rather than overt symptoms

The result was in doubt because the implications were that the person being tested had potentially been assaulted. The lab was asked to retest the original sample from the start and the result repeated HSV-2.

Contamination can arise in molecular testing within the lab from the environment samples are processed in or often from the area amplification occurs in due to a breach in the unidirectional workflow rule.

We have dedicated equipment in each area of testing from clean to dirty and we never move it backwards.

Regular environmental swabs are taken from each of these areas and tested for each of the pathogen targets of our PCR tests. If evidence is found of any pathogen in these samples the lab is scrubbed.

We use high grade detergents, enzymes to degrade contaminating DNA and RNA (yes RNA can be stable in the environment) and my very favourite thing bleach.

Repeat sampling of the environment occurs and if ‘clean’ we restart testing if still ‘dirty’ we repeat the process over and over until it’s ‘clean’

In my case, all environmental testing in the lab was clean as were the negative controls in the assays the two tests were undertaken in. Checked and checked again.

I discussed the case again with the clinician and explained that I didn’t believe there were issues with the lab results. What I then asked was whether there had been any patients in the clinic whom had presented with herpes either the same day or in the previous days before

The clinician went to check records and then came back to me to explain that indeed someone had presented two or three patients before our case, with primary genital herpes

We discussed the environment the sampling had been performed in and it was conceded that although cleaning was undertaken, it was feasible that areas such as the swab box and side tables where forms are stored could have been contaminated.

This would have been with virus so easily remedied at source by cleaning the entire environment (goodbye box of swabs).

What I’m trying to say is that contamination in molecular testing is common. We do our very best to mitigate it in the laboratory, but it can arise from any source and having proper audit trails and cleaning regimes in the lab.

The source can be found and sorted quickly, even if the lab isn’t at fault. It’s also a reminder that viruses stick to surfaces so when collecting samples please be mindful to keep the area or process as forensically clean as possible to avoid false positive results #COVID19