COVID-19 self-testing comparable to clinic-based testing
The performance of home-based midnasal swab collection for SARS-CoV-2 detection was comparable to clinic-based nasopharyngeal swab collection, according to a research letter published in JAMA Network Open.
The findings support the use of home swab collection, which could help increase access to testing while preserving personal protective equipment and minimizing the risk for exposure among health care workers, Helen Y. Chu, MD, MPH, infectious disease specialist at the University of Washington School of Medicine, and colleagues reported.
“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 contact tracing,” they wrote.
Chu and colleagues enrolled 158 symptomatic health care workers who presented to a drive-through clinic for testing, as well as 27 outpatients who recently tested positive for SARS-CoV-2. They provided participants with a midnasal swab for home self-collection. The performance of the self-collected swab was compared with nasopharyngeal swabs administered by medical assistants and nurses.
Forty-one participants (22.2%), including 14 health care workers, received a positive SARS-CoV-2 result with the clinician-collected nasopharyngeal swab, self-collected midnasal swab or both. Among these participants, 80.5% had myalgia, 68.3% had a cough and 63.4% had a fever.
Compared with clinician-collected swabs, self-collected swabs were associated with 80% (95% CI, 63-91) sensitivity and 97.9% (95% CI, 94-99.5) specificity, according to the researchers. There was a positive correlation between cycle thresholds — a semiquantitative measure of viral load — of the self-collected swabs vs. clinician-collected swabs (correlation coefficient, 0.81; P < .001).
The researchers identified 28 true-positive test results, where the participant tested positive for SARS-CoV-2 with the self-collected and clinician-collected swabs. They also identified seven false-negative results, where the participant tested positive with the clinician-collected swab but yielded a negative result with the self-collected swab.
On average, self-collected swabs were obtained sooner after symptom onset among the true positives than false negatives (median of 4 days vs. 6 days).
The researchers further analyzed five of the false-negative swabs. Among them, four had a cycle threshold greater than or equal to 33. In a sensitivity analysis of all swabs with a cycle threshold of less than or equal to 32, self-collected swabs were associated with a sensitivity of 95%.
“We observed false-negative results in samples with low initial viral loads,” Chu and colleagues wrote. “A home-based strategy should be targeted toward individuals early in illness, when risk of transmission is highest and care seeking less likely.”
Because most participants were health care workers, the generalizability of the findings to the general population are limited, according to the researchers. However, Chu said home swab collection is a relatively straightforward process.
“You basically stick the Q-tip up your nose, twirl it around a few times, put it in the tube and snap off the top,” she told Healio Primary Care. “When samples come back to the lab, we check for collection errors. We've done this for thousands of samples for the Seattle Flu Study. People who are health care workers and the vast majority who are not health care workers are able to do this without making mistakes.”
Recently, the FDA authorized emergency use of a different at-home test collection kit for COVID-19 developed by the health technology company Color. The dry nasal swab collection kit costs less than $1 per test, according to a press release from the manufacturer. The swab can be collected at home and returned by mail.
Home swab collection is not meant to replace testing in a clinic, Chu said. Instead, it represents another option for patients who may otherwise be hard to reach because of distance or immobility.
“For people who are in households with an infected case, this could be used for contact tracing,” she added. “There are advantages to this approach in certain populations, and it helps deal with the infection control issues of having a lot of infected people in your clinic.”
*Photo credit for Chu's headshot: UW Medicine
- Color. Color Receives Emergency Use Authorization for Unmonitored COVID-19 Testing Technology. https://www.color.com/color-receives-emergency-use-authorization-for-unmonitored-covid-19-testing-technology. Accessed July 27, 2020.
- McCulloch DJ, et al. JAMA Netw Open. 2020;doi:10.1001/jamanetworkopen.2020.16382.