Self-Swab COVID-19 Home Testing Found Comparable

Damian McNamara

July 22, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Symptomatic people seeking COVID-19 testing can effectively swab themselves at home, suggests a new study, which found that the results of such testing were comparable to those involving traditional nasopharyngeal swabbing by clinicians.

Home swab testing was 80% sensitive and 98% specific for detecting SARS-CoV-2 compared with testing administered by clinicians.

"As we continue to see a large number of cases across the US, timely testing needs to be a priority," senior study author Helen Y. Chu, MD, MPH, told Medscape Medical News. Home testing could also supplement traditional types of testing.

"At-home self-collected swabs provide a way for individuals to get tested quickly and accurately without needing to leave their home and potentially expose other individuals," added Chu, a professor of medicine in the Division of Allergy and Infectious Diseases at the University of Washington School of Medicine in Seattle.

The findings were published online July 22 in a research letter in JAMA Network Open.

An earlier study, reported in JAMA Network Open on June 12, also revealed good concordance between patient swabbing and clinician swabbing for COVID-19. In that study of 30 participants, researchers from Stanford University, in California, reported that patient-collected specimens were 100% sensitive and 95% specific.

To compare these approaches in a larger population, the investigators evaluated 185 people seeking COVID-19 testing, including healthcare workers.

They used custom-designed self-swab tests. The kit included a Copan FLOQSwab, BD Universal Transport Media, and other commercially available individual components. The researchers published an instruction sheet on creating the test kits on July 9 in The New England Journal of Medicine (supplemental Figure 2).

Positive Correlations

Overall, testing confirmed positive results in 41 of 185 participants (22%). Most participants ― 85% ― were healthcare workers. Within this group, 14 (9%) tested positive for SARS-CoV-2.

Chu and colleagues report "substantial agreement" between the two forms of testing, reflected by a Cohen kappa coefficient of 0.81.

Furthermore, the cycle thresholds of home swabs — an indication of the viral load — positively correlated with clinician swabs (correlation coefficient, 0.81; P < .001). When viral loads were high — defined as a cycle threshold of ≤32 — the sensitivity of home swabs increased to 95%.

When asked if the similar accuracy of the two testing approaches was unexpected, Chu said, "We weren't surprised. People are able to collect their own swabs, and we've shown previously that they do a good job collecting the samples." In previous studies, other respiratory pathogens, including influenza, were collected.

PPE-Sparing, Earlier Detection?

"Unsupervised home self-swab collection presents several advantages, including accessibility outside of the health care system and minimizing personal protective equipment use," the researchers note. "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."

A home-based strategy "should be targeted toward individuals early in illness, when risk of transmission is highest and care seeking less likely," they add.

One limit of the study is generalizability to the general public, because most participants were healthcare providers. "Of note, the vast majority of participants in this study were health care workers themselves, raising the question as to whether they may do a better job in collecting a sample, compared to the general public," Karen Kaul, MD, PhD, chair of the Department of Pathology and Laboratory Medicine at NorthShore University HealthSystem in Evanston, Illinois, told Medscape Medical News when asked to comment on the study.

"It is likely that clinicians would be more familiar with the swabbing process and have a better understanding of how to properly take a swab," Chu said. "However, people are pretty good at following instructions and collecting their own swab."

"This encouraging but small study examines the accuracy of self-collected mid-nasal samples for the detection of COVID, in comparison to the gold standard nasopharyngeal swabs collected by healthcare workers," Kaul said. This strategy would allow for broader public testing and would lessen the need for personal protective equipment and healthcare workers – "both of which are currently in short supply."

"The data showed that the self-collected samples yielded positive results on 80% of the positive samples — 20% were missed, likely due to the fact that mid-nasal and nasopharyngeal swabs were being compared. Most studies show that the mid-nasal swabs are somewhat less sensitive," Kaul added. She suggested that assays be performed on a platform with good sensitivity to ensure that even fewer cases are missed.

When asked whether self-swabbing could be utilized in drive-through COVID-19 testing sites, Chu said, "Yes, we believe our results are generalizable to any location where swabs are being self-collected. In our study, self-collection was performed in an unsupervised home setting, with participants following a set of printed instructions. If instructions provided at these drive-through testing sites are clear and concise, we would expect the same level of accuracy."

Additional limitations include possible sample degradation from shipping at ambient temperature and a difference in timing of sample collection between groups — the self-swab cohort took 1 day longer. This timeline could have affected viral load levels, the researchers note.

Multiple Studies Planned

With regard to future research, Chu said, "We are starting to do large-scale studies examining response to outbreaks and doing 'no-contact' contact tracing with this method."

The investigators also plan to compare viral loads and antibody levels using a biorepository of blood samples from people with confirmed SARS-CoV-2 infection.

Chu and colleagues will analyze swab samples taken within 48 hours of a positive test and compare them with swabs collected from those same patients every 2 to 3 days over 2 weeks to assess changes in viral loads and viral shedding over time.

Some Unanswered Questions

This study "raises an important issue that should be investigated further," Zvi G. Loewy, PhD, associate dean of research and professor of pharmaceutical and biomedical sciences at Touro College of Pharmacy in New York City, told Medscape Medical News when asked to comment.

"We are in the era of personalized medicine," Loewy said. "Individuals with diabetes routinely test their sugar levels. If the collection of specimens is well designed, it should be very feasible for patients to collect their own specimen for COVID-19 testing."

Unanswered questions from this study include whether self-collection minimizes COVID-19 exposure and whether self-testing does in fact expedite testing overall, he said. Regarding the study design, Loewy suggested similar studies in the future adopt a crossover design to compare two samples for each individual — one self-collected specimen and one collected by a trained clinician.

Chu and Loewy have disclosed no relevant financial relationships.

JAMA Netw Open. Published online July 22, 2020. Full text

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