At-home COVID tests: One negative result not enough, study says

WORCESTER – Anyone who gets a negative result for COVID-19 from an at-home rapid antigen test shouldn't assume they're not infected, and should keep testing, according to a safety recommendation Thursday from the U.S. Food and Drug Administration.

The guidance is based on research conducted by UMass Chan Medical School and partners supported by the National Institutes of Health.

If repeat testing isn’t done, an infection may be present and people could unknowingly spread COVID-19 to others, especially if they're not experiencing symptoms, according to the study.

"It's not enough to do a negative antigen test today and have confidence you’re not infected with the virus,” said Dr. Apurv Soni, assistant professor of medicine at Chan and the study's lead investigator.

Repeat testing is recommended after a negative test for those who show COVID-19 symptoms and for those who are asymptomatic but may have been exposed to the virus.

Published online in medRxiv, the study was paid for by the NIH and included more than 5,000 people nationwide over age 2.

Data was gathered between October 2021 and February.

For participants who were asymptomatic, the study found that two additional tests - the first taken 48 hours after the negative result and the second 48 hours later - are more likely to detect COVID-19 during the first week of infection.

Among the asymptomatic that had an infection lasting at least two days based on PCR testing, repeat testing three times at 48-hour intervals detected more than 75% of infections.

For those who were symptomatic, one additional test taken 48 hours after a negative test is more likely to detect COVID-19 during the first week of infection.

In that group, the rate of detection was more than 90% when testing started within the first week of infection.

Big difference

What separates this research effort from others, said Soni, is the larger number of participants – both symptomatic and asymptomatic – who were studied during the omicron variant, which is largely responsible for current COVID-19 infections.

“On a personal level, this study speaks to when antigen tests are useful and not useful, and how to use them,” said Soni.

Wear a face mask

Anyone suspected of contracting COVID-19 without showing symptoms should exercise caution by wearing a face mask and stay away from crowds, the study said.

They should continue that practice for at least six days until three at-home antigen tests taken 48 hours apart have been completed.

Study details

All 5,609 participants came from a group of more than 7,000 enrolled in a national “Test Us At Home” study conducted by the NIH’s Rapid Acceleration of Diagnostics Tech program.

Each person took an at-home antigen test using one of three retail test kits available in the U.S. They also collected a sample for a molecular PCR test, using nasal swabs for both types of test samples.

Tests were done every 48 hours for 15 days.

A new mobile application developed by Chan was used to enroll participants and report results.

Study partners included Quest Diagnostics, CareEvolution, community health centers and makers of rapid tests.

Common sense

Soni acknowledged the study is "common sense," because it reassures the public of something it probably already knew: Testing more often means a higher likelihood of infection detection.

However, Soni believes the study is valuable because it provides reassurance that antigen tests work, while giving clear guidance on how to use them.

“If there is concern you’re infected, and you want to make sure you’re not infected, one or two tests is not enough," said Soni. "Do three tests to make sure you’re not infected.”

Contact Henry Schwan at henry.schwan@telegram.com. Follow him on Twitter @henrytelegram

This article originally appeared on Telegram & Gazette: medical school Worcester COVID-19 rapid antigen test NIH FDA