SARS-CoV-2 identification and IgA antibodies in saliva: One sample two tests approach for diagnosis

Abstract

Aim: This study aims to verify whether standardized saliva collection is suitable for SARS-CoV-2 molecular detection and IgA measurement.

Methods: 43 COVID-19 inpatients and 326 screening subjects underwent naso-pharyngeal (NP)-swab and saliva collection (Salivette). Inpatients also underwent repeated blood collections to evaluate inflammation and organs involvement. In all patients and subjects, SARS-CoV-2 (gene E) rRT-PCR was undertaken in saliva and NP-swabs. Salivary IgA and serum IgA, IgG, IgM were measured on inpatients' samples.

Results: NP-swabs and saliva were both SARS-CoV-2 positive in 7 (16%) or both negative in 35 (82%) out of 43 patients successfully included in the study. NP-swabs and saliva results did not perfectly match in one patient (saliva positive, NP-swab negative). Positive molecular results were significantly associated with disease duration (p = 0.0049). 326/326 screening subjects were SARS-CoV-2 negative on both NP-swabs and saliva. Among the 27 saliva samples tested for IgA, 18 were IgA positive. Salivary IgA positivity was associated with pneumonia (p = 0.002) and CRP values (p = 0.0183), not with other clinical and molecular data, or with serum immunoglubulins.

Conclusions: A standardized saliva collection can be adopted to detect SARS-CoV-2 infection in alternative to NP-swabs. Preliminary data on salivary IgA support the use of saliva also for patient monitoring.

Keywords: Naso-pharyngeal swab; SARS-CoV-2; Saliva; Salivary IgA.

Fig. 1

The correlation between threshold cycle (Ct) values obtained with rRT-PCR and SARS-CoV-2 copy number/μl (ddPCR). Correlation between threshold cycles (Ct) and the copy number/μl obtained with ddPCR (expressed in log₂). Six SARS-CoV-2 positive naso-pharyngeal swabs (open circles) and corresponding saliva data (dots) are shown.

Fig. 2

The correlation between salivary IgA and biochemical and haematological markers. The correlation between salivary IgA and biochemical and haematological parameters. The upper panel shows the correlation between salivary IgA positive or negative findings and CRP values obtained at admission and enrolment. The lower panel shows the correlation between salivary IgA and white blood cell count at admission and enrolment.