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Nursing essay
Research Letter | Infectious Diseases
Comparison of Unsupervised Home Self-collected Midnasal Swabs
With Clinician-Collected Nasopharyngeal Swabs for Detection
of SARS-CoV-2 Infection
Denise J. McCulloch, MD, MPH; Ashley E. Kim, BS; Naomi C. Wilcox, MPH; Jennifer K. Logue, BS; Alex L. Greninger, MD, PhD; Janet A. Englund, MD; Helen Y. Chu, MD, MPH
Introduction
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 cliniciancollected nasopharyngeal swabs for COVID-19 diagnosis has not been well described.
Methods
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 selfcollection of a midnasal swab. Home swab performance was compared with clinician-collected
nasopharyngeal swabs, which were collected by medical Helpants 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.
Results
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
+ Supplemental content
Author affiliations and article information are
listed at the end of this article.
Open Access. This is an open access article distributed under the terms of the CC-BY License.
JAMA Network Open. 2020;3(7):e2016382. doi:10.1001/jamanetworkopen.2020.16382 (Reprinted) July 22, 2020 1/4
Downloaded From: https://jamanetwork.com/ on 02/14/2021
Table. Results of Clinician-Collected Nasopharyngeal Swabs vs Home Self-collected Midnasal Swabs
Self-collected MNS swab result
Median (IQR or range)
Total
Clinician-collected NPS result
Positive Negative Inconclusive
Positive, No. 28 3 0 31
NP swab viral load 24.1
(18.7-26.0)
NA NA 24.1
(18.7-26.0)
Self-swab viral load 22.6
(19.1-27.3)
32.9
(32.7-33.2)
NA 22.8
(19.3-28.4)
Days between symptom onset and NP swab 3.0
(1.0-6.0)
4.0
(2.5-8.5)
NA 3.0
(1.0-6.0)
Days between MNS and NPS (range) 1.0
(0.0-2.0)
0.0
(0.0-0.0)
NA 1.0
(0.0-2.0)
Negative, No. 7 140 1 148
NP swab viral load 33.7
(33.5-35.1)
NA 37.4 34.4
(33.5-36.8)
Self-swab viral load NA NA NA NA
Days between symptom onset and NP swab 5.0
(2.5-13.0)
2.0
(1.0-4.0)
2.0 2.0
(1.0-4.0)
Days between MNS and NPS (range) 1.0
(0.0-1.0)
0.0
(−4.0 to 7.0)
0.0 0.0
(−4.0 to 7.0)
Inconclusive, No.a 3 3 06
NP swab viral load 32.9
(30.2-33.4)
NA NA 32.9
(30.2-33.4)
Self-swab viral load 37.8
(37.3-37.9)
37.0
(37.0-37.0)
NA 37.4
(37.0-37.8)
Days between symptom onset and NP swab 5.5
(5.3-5.8)
1.5
(1.3-1.8)
NA 3.5
(1.8-5.3)
Days between MNS and NPS (range) 1.0
(1.0-1.0)
0.0
(0.0-0.0)
NA 0.5
(0.0-1.0)
Total, No. 38 146 1 185
NP swab viral load 24.5
(21.9-30.1)
NA 37.4 24.7
(22.3-31.8)
Self-swab viral load 22.9
(19.4-28.8)
33.4
(32.9-35.2)
NA 24.9
(19.9-32.9)
Days between symptom onset and NP swab 3.0
(2.0-6.0)
2.0
(1.0-4.0)
2.0 2.0
(1.0-5.0)
Days between MNS and NPS (range) 1.0
(0.0-2.0)
0.0
(−4.0 to 7.0)
0.0 0.0
(−4.0 to 7.0)
Abbreviations: IQR, interquartile range; MNS, midnasal
swab; NA, not applicable; NPS, nasopharyngeal swab.
a Positive result was defined as both of 2 primers
positive, and inconclusive was defined as 1 of 2
probes for severe acute respiratory coronavirus 2
polymerase reaction positive and 1 negative.
Figure. Cycle Thresholds (Ct) for Home Self-collected Midnasal Swabs and Clinician-Collected
Nasopharyngeal (NP) Swabs
40
30
20
35
25
15
10
10 40
Ct value of midnasal swab self-collected at home
Ct value of clinician-collected NP swab
15 20 25 30 35
R=0.81; P=5.1×10–6
Home self-collected midnasal swab (n = 28) Ct values
were positively associated with the paired cliniciancollected 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.
JAMA Network Open | Infectious Diseases Self-collected Midnasal vs Clinician-Collected Nasopharyngeal Swabs to Detect SARS-CoV-2 Infection
JAMA Network Open. 2020;3(7):e2016382. doi:10.1001/jamanetworkopen.2020.16382 (Reprinted) July 22, 2020 2/4
Downloaded From: https://jamanetwork.com/ on 02/14/2021
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%.
Discussion
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 SARSCoV-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.
ARTICLE INFORMATION
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 (dmccull@uw.edu).
Author Affiliations: Department of Medicine, Division of Allergy and Infectious Diseases, University of
Washington, Seattle (McCulloch, Kim, Wilcox, Logue, Chu); Department of Laboratory Medicine, University of
Washington, Seattle (Greninger); Seattle Children’s Research Institute, Seattle, Washington (Englund).
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.
JAMA Network Open | Infectious Diseases Self-collected Midnasal vs Clinician-Collected Nasopharyngeal Swabs to Detect SARS-CoV-2 Infection
JAMA Network Open. 2020;3(7):e2016382. doi:10.1001/jamanetworkopen.2020.16382 (Reprinted) July 22, 2020 3/4
Downloaded From: https://jamanetwork.com/ on 02/14/2021
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),
Helped with acquisition of data. Jay Shendure, MD, PhD (University of Washington, Seattle; Brotman Baty
Institute, Seattle; and Howard Hughes Medical Institute, Chevy Chase, Maryland), Helped 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), Helped 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), Helped 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.
REFERENCES
1. Seaman CP, Tran LTT, Cowling BJ, Sullivan SG. Self-collected compared with professional-collected swabbing in
the diagnosis of influenza in symptomatic individuals: a meta-analysis and assessment of validity.J Clin Virol.
2019;118:28-35. doi:10.1016/j.jcv.2019.07.010
2. He Z, Zhuang H, Zhao C, Dong Q, Peng G, Dwyer DE. Using patient-collected clinical samples and sera to detect
and quantify the severe acute respiratory syndrome coronavirus (SARS-CoV). Virol J. 2007;4:32. doi:10.1186/1743-
422X-4-32
3. Zou L, Ruan F, Huang M, et al. SARS-CoV-2 viral load in upper respiratory specimens of infected patients. N Engl
J Med. 2020;382(12):1177-1179. doi:10.1056/NEJMc2001737
4. Wikramaratna P, Paton RS, Ghafari M, Lourenco J. Estimating false-negative detection rate of SARS-CoV-2 by
RT-PCR. medRxiv. Preprint posted online April 14, 2020. doi:10.1101/2020.04.05.20053355
5. Chu HY, Englund JA, Starita LM, et al; Seattle Flu Study Investigators. Early Detection of Covid-19 through a
Citywide Pandemic Surveillance Platform. N Engl J Med. 2020. doi:10.1056/NEJMc2008646
SUPPLEMENT.
eAppendix. Supplemental methods
eReferences.
eFigure. Clinical study methods for enrollment of symptomatic healthcare workers presenting for drive-up testing
and community outpatients with positive SARS-CoV-2 tests
JAMA Network Open | Infectious Diseases Self-collected Midnasal vs Clinician-Collected Nasopharyngeal Swabs to Detect SARS-CoV-2 Infection
JAMA Network Open. 2020;3(7):e2016382. doi:10.1001/jamanetworkopen.2020.16382 (Reprinted) July 22, 2020 4/4
Downloaded From: https://jamanetwork.com/ on 02/14/2021
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