Supervised self-sampling of the anterior nose (AN) for COVID-19 infection was found to be comparable with professional nasopharyngeal (NP) sampling. These findings were published in the European Respiratory Journal as a research letter to the editor.
The World Health Organization (WHO) has approved 2 antigen-detecting rapid diagnostic tests (Ag-RDTs) by NP swab for SARS-CoV-2. However, NP swab tests are often uncomfortable and must be administered by healthcare professionals wearing personal protective equipment.
Testing via AN swabs has the potential to be self-administered and when combined with Ag-RDT technology, may allow for the expansion of rapid COVID-19 self-monitoring.
Volunteers (N=289) for this head-to-head prospective study underwent a self-collected bilateral AN swab following verbal instructions and combined oral/nasal swab and NP swab collected by healthcare staff. Verbal instructions for the self-administered swab were to insert the swab horizontally into the nostril 2 to 3 cm and rotate for 15 seconds against both sides of the nasal wall.
The self-administered AN swabs and NP swabs were tested with the Ag-RDT (STANDARD Q COVID-19 Ag Test), and the oral/nasal swab was assessed by real-time polymerase chain reaction (RT-PCR). All collections occurred from September 23 to October 14, 2020, at the Charité University Hospital in Germany.
Participants had a mean age of 34.7 years, 42.9% were women, 19.0% had comorbidities, and 97.6% had been experiencing symptoms consistent with COVID-19 for an average of 4.4 days.
A total of 13.5% of study participants tested positive for SARS-CoV-2 infection by NP. All but 2 of the positive individuals also tested positive by AN, and no patients tested positive by AN alone. This agreement corresponded with a high positive percent agreement (90.6%; 95% CI, 75.8-96.8), negative percent agreement (99.2%; 95% CI, 97.2-99.8), and inter-rater reliability (AN: k, 0.98; NP: k, 1.0).
The 2 discrepant tests were from an individual with low viral load (10 days after symptom onset) and an individual who gently swabbed their nose (user error).
The overall Ag-RDT sensitivity was 74.4% (95% CI, 58.9-85.4) and specificity was 99.2% (95% CI, 97.1-99.8) compared with RT-PCR results. Among only those with a high viral load (>7.0 log10 RNA SARS-CoV-2/swab), sensitivity with AN sampling (95.7%; 95% CI, 79.0-99.8) and NP sampling (100%; 95% CI, 85.7-100) was higher.
This study was limited by the fact that NP swabs were generally administered in a manner not recommended by the manufacturer; however, the health care staff found it difficult to administer per protocol.
The letter authors concluded that self-administered AN swabs tested by Ag-RDT may be a viable rapid assessment for SARS-CoV-2 that can be easily administered at home.
Lindner AK, Nikolai O, Kausch F, et al. Head-to-head comparison of SARS-CoV-2 antigen-detecting rapid test with self-collected anterior nasal swab versusprofessional-collected nasopharyngeal swab. Eur Respir J. 2020;57(3). doi:10.1183/13993003.03961-2020