Detection of SARS-CoV-2 RNA residue on object surfaces in nucleic acid testing laboratory using droplet digital PCR

The rapid development of global COVID-19 pandemic poses an unprecedented challenge to the safety and quality of laboratory diagnostic testing. Little is known about the laboratory surface areas and operation behaviors that may cause potential contamination in SARS-CoV-2 nucleic acid testing. This study aims to provide reference basis for the improvement of laboratory disinfection programs and personal operating protocols. In this study, we compared the qRT-PCR and ddPCR in detecting of residual virus that existed on the object surfaces from sample transportation and reception related facilities, testing related instruments, personal protective equipment and other facilities in nucleic acid testing laboratory. All samples were negative by qRT-PCR, in contrast, 13 of 61 samples were positive for SARS-CoV-2 by ddPCR. The areas with highest density of SARS-CoV-2 nucleic acid were the outer gloves of operator A (37.4 copies/cm²), followed by door handle of 4 °C refrigerator (26.25 copies/cm²), goggles of operator A (22.16 copies/cm²), outer cover of high speed centrifuge (19.95 copies/cm²), inner wall of high speed centrifuge (14.70 copies/cm²) and others. We found that all the positive objects were directly or indirectly contacted by the operator's gloved hands, suggesting that hands contact was the main transmission pathway that led to laboratory environmental contamination. In summary, ddPCR has an advantage over qRT-PCR in tracing laboratory contamination. We evaluated the risk areas and operation behaviors that may easily cause contamination, and provided recommendation for improving the laboratory disinfection programs and personal operating specifications.