Viral load may impact the diagnostic performance of nasal swabs in nucleic acid amplification test and quantitative antigen test for SARS-CoV-2 detection

ElsevierVolume 28, Issue 11, November 2022, Pages 1590-1593Journal of Infection and ChemotherapyAbstractIntroduction

Compared to nasopharyngeal swabs (NPS), there has been insufficient evaluation of the diagnostic performance of nasal swabs (NS) for the detection of severe acute respiratory coronavirus 2 (SARS-CoV-2) in the nucleic acid amplification test (NAAT) and quantitative SARS-CoV-2 antigen test (QAT).

Methods

We prospectively compared healthcare worker-collected and flocked NS within nine days after symptom onset to paired NPS to detect SARS-CoV-2 in NAAT and QAT on the fully automated Lumipulse system. The agreement between sample types was evaluated, and cycle threshold (Ct) values and antigen levels were used as surrogate viral load measures.

Results

Sixty sets of NPS and NS samples were collected from 40 patients with COVID-19. The overall agreements between NAAT and QAT samples were 76.7% and 65.0%, respectively. In NAAT, the Ct value of NS was significantly higher, 5.9, than that of NPS. Thirty-nine (95.1%) NS tested positive in 41 positive-paired NPS with Ct ≤ 30. The negative correlation was observed between antigen levels of NS in QAT and Ct values of NS in NAAT (r = −0.88). In QAT, the antigen level of NS was significantly lower than that of NPS. Thirty-six (90.0%) NS tested positive in 40 positive-paired NPS with antigen levels >100 pg/mL, which were collected significantly earlier than those with antigen levels ≤100 pg/mL.

Conclusions

In NAAT and QAT, NS had limited performance in detecting SARS-CoV-2 compared to NPS. However, NS may be helpful for patients with COVID-19 with high viral loads or those in the early stages of the illness.

Keywords

Nasal swabs

Nasopharyngeal swabs

SARS-CoV-2

Nucleic acid amplification test

Quantitative SARS-CoV-2 antigen test

Viral load

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© 2022 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.

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