Evaluation of a saliva molecular point of care for the detection of SARS-CoV-2 in ambulatory care

Abstract

Rapid identification of SARS-CoV-2-infected individuals is a cornerstone for the control of virus spread. The sensitivity of SARS-CoV-2 RNA detection by RT-PCR is similar in saliva and nasopharyngeal swabs. Rapid molecular point-of-care tests in saliva could facilitate, broaden and speed up the diagnosis. We conducted a prospective study in two community COVID-19 screening centers to evaluate the performances of a CE-marked RT-LAMP assay (EasyCoV) designed for the detection of SARS-CoV2 RNA from fresh saliva samples, compared to nasopharyngeal RT-PCR, to saliva RT-PCR and to nasopharyngeal antigen testing. Overall, 117 of the 1718 participants (7%) tested positive with nasopharyngeal RT-PCR. Compared to nasopharyngeal RT-PCR, the sensitivity and specificity of the RT-LAMP assay in saliva were 34% and 97%, respectively. The Ct values of nasopharyngeal RT-PCR were significantly lower in the 40 true positive subjects with saliva RT-LAMP (Ct 25.9) than in the 48 false negative subjects with saliva RT-LAMP (Ct 28.4) (p = 0.028). Considering six alternate criteria for reference tests, including saliva RT-PCR and nasopharyngeal antigen, the sensitivity of saliva RT-LAMP ranged between 27 and 44%. The detection of SARS-CoV-2 in crude saliva samples with an RT-LAMP assay had a lower sensitivity than nasopharyngeal RT-PCR, saliva RT-PCR and nasopharyngeal antigen testing.Registration number: NCT04578509.

Performances of rapid and connected salivary RT-LAMP diagnostic test for SARS-CoV-2 infection in ambulatory screening

“…The worked performed by LeGoff and collaborators was also carried out in France but a few months later than ours and the prevalence of positive participants were similar between the two studies using NP RT-qPCR test (7% for both studies) 21 . On the other hand, when saliva was used as specimen, the prevalence found by LeGoff was clearly lower compared to our clinical study (9% and 5% against 15.2% and 14.2%) using saliva RT-qPCR and saliva RT-LAMP, respectively.…”

“…Accordingly, we showed the feasibility of saliva self-sampling in asymptomatic or mildly symptomatic outpatients. Despite NPS being the most used sampling method, saliva was demonstrated to be a reliable specimen for the detection of SARS-CoV-2 in other several studies 6 , 8 , 9 , 11 , 21 , 32 , 41 – 43 and our results showed that saliva presents a superior performance for COVID-19 diagnosis using RT-qPCR compared to NPS.…”

“…SARS-CoV-2 is detected in various human specimens but none of diagnostic test is ideal for COVID-19 19 – 21 mass screening. Considering the high specificity of the existing RT-qPCR for SARS-CoV-2 detection, it is relevant to consider an individual as being infected when a RT-qPCR test is positive independently of the specimen 18 , 22 .…”

“…By comparison, a recent meta-analysis showed saliva NAAT pooled sensitivity of 83.2% and specificity of 99.2% 14 . The EasyCOV® RT-LAMP test was also recently evaluated against NP RT-PCR, saliva RT-PCR and NP antigenic tests by LeGoff and collaborators 21 . In this study, the authors reported a sensitivity and a specificity of 34% (95%CI 26–44) and 97% (95%CI 96–98), respectively.…”

“…Besides, LeGoff et al reported that the result of the RT-LAMP test was performed using a pH sensitive reagent 21 . Actually, the specifications of the EasyCOV® RT-LAMP assay explicitly mention that the use of the intercalant reagent SYBR green is requested to reveal the presence of the amplicons in the reaction tube even for colorimetric readout.…”