Inactivation of SARS-CoV-2 virus in saliva using a guanidium based transport medium suitable for RT-PCR diagnostic assays


Upper respiratory samples used to test for SARS-CoV-2 virus may be infectious and present
a hazard during transport and testing. A buffer with the ability to inactivate SARS-CoV-2 at
the time of sample collection could simplify and expand testing for COVID-19 to non-conventional

We evaluated a guanidium thiocyanate-based buffer, eNAT™ (Copan) as a possible transport
and inactivation medium for downstream Reverse Transcriptase-Polymerase Chain
Reaction (RT-PCR) testing to detect SARS-CoV-2. Inactivation of SARS-CoV-2 USA-WA1/
2020 in eNAT and in diluted saliva was studied at different incubation times. The stability of
viral RNA in eNAT was also evaluated for up to 7 days at room temperature (28˚C), refrigerated
conditions (4˚C) and at 35˚C.

SARS-COV-2 virus spiked directly in eNAT could be inactivated at >5.6 log10 PFU/ml within
a minute of incubation. When saliva was diluted 1:1 in eNAT, no cytopathic effect (CPE) on
VeroE6 cells was observed, although SARS-CoV-2 RNA could be detected even after 30
min incubation and after two cell culture passages. A 1:2 (saliva:eNAT) dilution abrogated
both CPE and detectable viral RNA after as little as 5 min incubation in eNAT. SARS-CoV-2
RNA from virus spiked at 5X the limit of detection remained positive up to 7 days of incubation
in all tested conditions.

eNAT and similar guanidinium thiocyanate-based media may be of value for transport, stabilization,
and processing of clinical samples for RT-PCR based SARS-CoV-2 detection.