Why COVID-19 Laboratory Personnel Should Be Tested Before Attending the Laboratory: how even the most experienced personnel conta350minate clinical samples

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in a pandemic (1). Early diagnosis and testing of symptomatic individuals and asymptomatic carriers (2) remain essential since the latter group can transmit the virus (3,4). Current assays for SARS-CoV-2 detection are mostly based on quantitative real-time PCR (RT-qPCR)(5). However, cross-contamination remains a challenge in RT-qPCR assays. Here, we would like to share the most interesting route of sample contamination in SARS-CoV-2 molecular diagnosis laboratories and the necessity of personnel testing. We set up our molecular diagnosis laboratory three months ago using RT-qPCR. We strictly adhered to biosafety guidelines to ensure personnel safety and avoid cross-contamination of samples. We use (i) two extraction negative controls (EXNC), (ii) one no template control for every 10 samples, and (iii) one negative control. Note that to minimize the probability of contamination, the positive control was prepared last, after each patient’s sample was added to the corresponding tube. After one month and a half, we noticed a slightly positive signal (Cq = 38) in one of the EXNC. Upon repeating the run, both EXNC showed a Cq = 38. We narrowed down the cause to the personnel. Thus, all the personnel were tested for SARS-CoV-2 by the reference laboratory of the Pasteur Institute of Iran.