Validation of a Sars-Cov-2 Nucleocapside N-Protein Detection Test in Saliva

ABSTRACT

An antigenic method for the quantification of SARS-CoV-2 nucleocapside protein (LUMIPULSE SARS-CoV-2 Ag- Fujirebio) both on naso-pharyngeal swab and on saliva has been evaluated on three groups of subjects: sub-intensive care unit hospitalized patients (n=24), patients discharged from this unit (n=22), controls (n=74). The molecular RT-PCR technique was considered the reference method. The cut-off value of 1.04 pg/mL distinguishes sick (hospitalized) from healthy (controls) with sensibility=0.937 and specificity=0.959;area under the ROC curve (0.978);efficiency=0.90. On saliva the qualitative antigenic result (positive if >cut-off) agrees with the qualitative molecular one (k=0.84). Stratifying by groups, in the hospitalized group (with clear prevalence of positives) there is a concordance of the positives of 97%;in the two groups of patients discharged and controls (with clear prevalence of negatives) there is a concordance on the negatives of 91% and 96%, respectively. The qualitative antigenic result on saliva samples is concordant with the molecular qualitative one on the naso-pharyngeal swab (k=0.76).