Home self-collected midnasal swab (n = 28) Ct values were positively associated with the paired clinician-collected nasopharyngeal swab (n = 30) Ct value (correlation coefficient, 0.81; P = 5.1 × 10−6). The Ct values were calculated from a severe acute respiratory syndrome coronavirus 2 reverse transcriptase–polymerase chain reaction assay that targets 2 distinct regions of the virus, using Centers for Disease Control and Prevention primers and probes for the virus nucleocapsid (N) gene, N1 and N2.
eAppendix. Supplemental methods
eFigure. Clinical study methods for enrollment of symptomatic healthcare workers presenting for drive-up testing and community outpatients with positive SARS-CoV-2 tests
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McCulloch DJ, Kim AE, Wilcox NC, et al. Comparison of Unsupervised Home Self-collected Midnasal Swabs With Clinician-Collected Nasopharyngeal Swabs for Detection of SARS-CoV-2 Infection. JAMA Netw Open. 2020;3(7):e2016382. doi:10.1001/jamanetworkopen.2020.16382
Increased diagnostics are urgently needed to contain the spread of coronavirus disease 2019 (COVID-19). Home self-collected swabs may increase testing access while minimizing exposure risk to health care workers and depletion of personal protective equipment, allowing for early community detection of COVID-19. A comparison of unsupervised home self-collected swabs with clinician-collected nasopharyngeal swabs for COVID-19 diagnosis has not been well described.
This cross-sectional study was approved by the University of Washington institutional review board and follows the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline. Participants provided electronic informed consent. 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 (eFigure and eAppendix in the Supplement). 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. Cycle thresholds (Ct) are a semiquantitative measure of viral load. 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 2 qualitative test results. The threshold for statistical significance was set at 2-tailed P < .05.
Of 185 total participants, 158 (85%) 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. One hundred fifty-eight participants (85%) were health care workers, of whom 14 (9%) tested positive. Among participants with COVID-19, common symptoms included myalgia (33 participants [80.5%]), cough (28 participants [68.3%]), and fever (26 participants [63.4%]). Compared with clinician swabs, sensitivity and specificity of home swabs was 80.0% (95% CI, 63%-91%) and 97.9% (95% CI, 94%-99.5%), respectively (Table). Cohen κ statistic was 0.81 (95% CI, 0.70-0.93), suggesting substantial agreement.
Cycle thresholds of home swabs were positively correlated with clinician swabs (correlation coefficient, 0.81; P < .001) (Figure). Time from symptom onset to swab collection was comparable between true positives and false negatives. Among the 28 true positives, home swab collection occurred a median (interquartile range) of 4 (2-7) days after symptom onset, whereas among 7 false negatives, home swab collection occurred a median (interquartile range) of 6 (3-18) days after symptom onset (P = .32). The median (interquartile range) Ct of the clinician swab was lower for true positives vs false negatives (24.1 [18.7-26.0] vs 33.7 [33.5-35.1]; P = .01). Four of 5 false-negative swabs had Ct greater than or equal to 33. In a sensitivity analysis of all swabs with Ct less than or equal to 32, sensitivity of home swabs was 95%.
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. During this rapidly evolving pandemic, we enrolled 185 individuals presenting for SARS-CoV-2 testing, including 41 with positive test results. We used novel home-based swab self-collection and rapid delivery services, thus avoiding participant contact with the health care system.
Unsupervised home self-swab collection presents several advantages, including accessibility outside of the health care system and minimizing personal protective equipment use. This approach is safe and scalable in the pandemic setting, permitting widespread testing of symptomatic participants early in illness and the potential for prompt self-isolation and contract tracing. The sensitivity of home self-collection in this study was lower than previously described.1 We observed false-negative results in samples with low initial viral loads.2-4 A home-based strategy should be targeted toward individuals early in illness, when risk of transmission is highest and care seeking less likely.
Limitations of the study include shipping at ambient temperature, which may have led to sample degradation. However, we have demonstrated stability of respiratory viruses at ambient temperatures up to 9 days.5 Second, home self-collection often occurred 1 day after clinician collection, likely leading to samples with lower viral load. Third, many participants were health care workers, potentially limiting generalizability to the general population. Fourth, clinician-collected swabs are an imperfect criterion standard that may introduce bias.
As societies reopen, expansion of testing is critical for preventing a global resurgence in COVID-19. Home swab collection has the potential to play a pivotal role in increasing testing access across the broader population.
Accepted for Publication: June 29, 2020.
Published: July 22, 2020. doi:10.1001/jamanetworkopen.2020.16382
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 McCulloch DJ et al. JAMA Network Open.
Corresponding Author: Denise J. McCulloch, MD, MPH, UW Medicine, 750 Republican St, Chu Lab Room E630, Box 358061, Seattle WA 98109 (firstname.lastname@example.org).
Author Contributions: Dr McCulloch had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: McCulloch, Kim, Englund, Chu.
Acquisition, analysis, or interpretation of data: McCulloch, Wilcox, Logue, Greninger, Englund.
Drafting of the manuscript: McCulloch, Wilcox, Englund, Chu.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: McCulloch, Wilcox.
Obtained funding: Englund, Chu.
Administrative, technical, or material support: Kim, Logue, Greninger, Englund.
Supervision: Logue, Greninger, Chu.
Conflict of Interest Disclosures: Dr Chu reported consulting with GlaxoSmithKline and Merck and receiving research funding from Sanofi Pasteur, Cepheid, and Ellume outside of the submitted work. Dr Greninger reported receiving personal fees from Abbott Molecular outside of the submitted work. Dr Englund reported consulting with Sanofi Pasteur and Meissa Vaccines outside the submitted work. No other disclosures were reported.
Funding/Support: This work was supported by Gates Ventures.
Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Additional Contributions: Caitlin Wolf, BS, and Gregory Pepper, BS (both of University of Washington, Seattle), assisted with acquisition of data. Jay Shendure, MD, PhD (University of Washington, Seattle; Brotman Baty Institute, Seattle; and Howard Hughes Medical Institute, Chevy Chase, Maryland), assisted with concept and design, obtaining funding, and critical revision of the manuscript. James P. Hughes, PhD (Fred Hutchinson Cancer Research Center, Seattle, and University of Washington, Seattle), assisted with statistical analysis and critical revision of the manuscript. Michael J. Boeckh, MD, PhD (University of Washington, Seattle; Brotman Baty Institute, Seattle; and Fred Hutchinson Cancer Research Center, Seattle), Keith R. Jerome, MD, PhD (University of Washington, Seattle, and Fred Hutchinson Cancer Research Center, Seattle), and Michael Jackson, PhD (Kaiser Permanente Washington Health Research Institute, Seattle), assisted with critical revision of the manuscript. We also acknowledge the University of Washington medical students who volunteered to help with this study. None of these individuals received financial compensation for their contributions to the study.