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Self-Collected Midnasal vs. Clinician-Collected Nasopharyngeal Swabs to Detect SARS-CoV-2
Quick Takes
- Home midnasal swab collection was fairly comparable to clinician-collected nasopharyngeal swab collection for detection of SARS-CoV-2 symptomatic patients, particularly those with higher viral loads.
- Of note, the sensitivity of home self-collection in this study was lower than previously described with false-negative results in samples with low initial viral loads.
- Overall, home testing avenue is safe and scalable in the pandemic setting, allowing for widespread testing of symptomatic individuals early in illness with the potential for prompt self-isolation and contract tracing, thus minimizing spread.
Study Questions:
How do unsupervised home self-collected nasal swabs compare with clinician-collected nasopharyngeal swabs for coronavirus disease 2019 (COVID-19) diagnosis?
Methods:
The investigators conducted a cross-sectional study and study participants were recruited from symptomatic outpatients testing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)–positive and symptomatic health care workers presenting to drive-through clinics. Participants were provided test kits for unsupervised home self-collection of a midnasal swab. Home swab performance was compared with clinician-collected nasopharyngeal swabs, which were collected by medical assistants and nurses. Positive test results for SARS-CoV-2 by both approaches were defined as true positives. Results with a positive clinician swab and negative home swab were defined as false negatives. Sensitivity was defined as true positives divided by the sum of true positives and false negatives. Cohen κ was calculated for agreement between the two qualitative test results. The threshold for statistical significance was set at two-tailed p < 0.05.
Results:
Of 185 total participants, 158 (85%) were enrolled at drive-through clinics, and 27 (15%) enrolled after a positive SARS-CoV-2 test. Among the 185 participants, 41 (22.2%) yielded SARS-CoV-2–positive test results via clinician-collected nasopharyngeal swab, home self-collected midnasal swab, or both. Compared with clinician swabs, sensitivity and specificity of home swabs was 80.0% (95% confidence interval [CI], 63%-91%) and 97.9% (95% CI, 94%-99.5%), respectively. Cohen κ statistic was 0.81 (95% CI, 0.70-0.93), suggesting substantial agreement. Cycle thresholds is a semiquantitative measure of viral load. Cycle thresholds of home swabs were positively correlated with clinician swabs (correlation coefficient, 0.81; p < 0.001).
Conclusions:
The authors concluded that unsupervised home midnasal swab collection was comparable to clinician-collected nasopharyngeal swab collection for detection of SARS-CoV-2 in symptomatic patients, particularly those with higher viral loads.
Perspective:
This cross-sectional study reports that home midnasal swab collection was fairly comparable to clinician-collected nasopharyngeal swab collection for detection of SARS-CoV-2 symptomatic patients, particularly those with higher viral loads. Of note, the sensitivity of home self-collection in this study was lower than previously described, with false-negative results in samples with low initial viral loads. Despite this limitation, unsupervised home self-swab collection has several advantages, including accessibility outside of the health care system, and minimizes personal protective equipment use. Furthermore, the home testing avenue is safe and scalable in the pandemic setting, allowing for widespread testing of symptomatic individuals early in illness with the potential for prompt self-isolation and contract tracing, thus minimizing spread.
Clinical Topics: COVID-19 Hub, Prevention
Keywords: Coronavirus, COVID-19, Diagnostic Tests, Routine, False Negative Reactions, False Positive Reactions, Health Personnel, Outpatients, Primary Prevention, SARS Virus, Sensitivity and Specificity, severe acute respiratory syndrome coronavirus 2, Viral Load
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