A comparison of the performance of saliva and nasopharyngeal nucleic acid amplification testing for the detection of SARS-CoV-2 in New Zealand.

AIM: To compare detection of SARS-CoV-2 from paired nasopharyngeal swabs (NPS) and saliva using molecular methods in common use for testing swabs in New Zealand.

METHOD: Samples from individuals testing positive for SARS-CoV-2 in Auckland, Wellington and Dunedin were tested at the local laboratories using methods previously established for these sample types.

RESULTS

One hundred and ninety-six paired samples from unique individuals were tested, with 46 (23%) positive from either sample type, of which 43/46 (93%) tested positive from NPS, and 42/46 (91%) from saliva, indicating no significant difference in performance between sample types (p=0.69). The average Δ Ct between saliva and nasopharyngeal swabs overall across the sample set was 0.22 cycles, indicating excellent concordance; however, the difference between NPS and saliva collected from the same individual was quite variable with up to 19 cycles difference between the sample types.

CONCLUSION

We found that saliva is an equivalent sample type to nasopharyngeal swab for the detection of SARS-CoV-2 in our laboratories using multiple assay combinations and is suitable for use as a diagnostic and surveillance test for selected groups of individuals.