According to new studies highlighted by multiple national outlets, the omicron variant may require slight adjustments to testing protocols in order to effectively identify early positive cases. The findings come as omicron has dominated state cases in recent weeks, including the Denver metro.
The preliminary findings highlight the importance of modifying COVID-19 protocols per variant in a timely fashion to remain successful in managing community transmission.
Current testing recommendations by the Centers for Disease Control and Prevention are to test five to seven days after exposure, or when symptoms develop. The latest findings not yet featured on the CDC’s website indicate that rapid antigen tests—such as those used by the state home kits and recommended by the City of Denver’s website—may be less effective at identifying positive cases in the first several days of exposure to omicron than for previous variants.
Results from the polymerase chain reaction, or PCR, tests completed by certified laboratories appear to remain capable of earlier detection for omicron, and other studies have confirmed the antigen tests work in high viral load cases.
No changes have formally been made to testing protocols due to the early and mixed nature of the studies, yet these findings suggest caution in test interpretation. If rapid antigen tests may more often provide false negatives during early infectious periods, these tests should be deemed less reliable for early testing. To detect positive cases with omicron, antigen tests were found to perform best at a median of three days after being detectable by PCR.
The possible reduced sensitivity of antigen tests may be related to sampling methods.
Although it is typical for respiratory diseases to be sampled via nasal swab, some experts now suggest that throat swabs may yield more active virus for omicron. This had led to speculation that the new variant takes up residence more strongly in oral cavities rather than nasal passages as compared to prior variants. It may also account for why omicron appears to carry a lower percentage of cases presenting with anosmia, a loss of smell, and why more omicron cases report early symptoms that include a sore or scratchy throat.
Scientific consensus on how to best sample for omicron remains unclear for now as studies are few and early. The Food and Drug Administration does not currently recommend throat swabs be performed by at-home users, citing risks to health if done improperly and clarifying that no throat swab tests have proven these to be safe and effective for omicron as of yet.
Yet many experts have taken an opposing stance, openly stating that if a throat swab is able to be safely conducted, they might consider first swabbing a patient’s throat and then swabbing their nose to increase the likelihood of early detection by antigen testing.
In Denver, both antigen and PCR testing is available, although tests have been limited as cases climb. There is also no readily available guidance on either the state or the City of Denver website to outline more recent concerns of false negatives with early antigen testing.
Until findings are more robust and public guidance is updated, residents able to access antigen tests should be aware of a potentially higher propensity for false negatives, thereby leading to a potentially false sense of security.
To reduce the likelihood of false negatives with antigen tests, residents can choose to wait to test until at least three days after symptoms begin, isolating in the meantime, or seek access to PCR testing immediately. Throat swabs have not been tested for approval.
Denver community testing sites that remain open according to the city website include:
5th Street Garage at the Auraria Campus – Monday to Friday from 8 a.m. to 6 p.m.
All City Stadium South – Monday to Friday from 7 a.m. to 5 p.m.
Clayton Early Learning – Mondays, Wednesdays and Fridays from 7 a.m. to 9:30 a.m.
George Washington High School – Monday to Friday from 7 a.m. to 5 p.m.
The Kunsmiller Creative Arts Academy – Monday to Friday from 9:30 a.m. to 6 p.m. (closed from 3:30 to 4:30 p.m. daily) and Saturdays from 7 a.m. to noon
Rocky Mountain Prep – Monday to Friday from 7 a.m. to 5 p.m.
Union Station – Monday to Friday from 7 a.m. to 3 p.m. and Saturdays from 7 a.m. to noon.
Additional testing locations include pharmacies at CVS, Health Mart, King Soopers, Walgreens and Walmart. Most offer access to both PCR and antigen testing opportunities as available.
Note: The information above was up to date as of Jan. 12 when this issue went to the printer. These sites are subject to intermittent closings based on staffing and testing availability, and generally include PCR options. Early registration to avoid waiting lines can be found on the City of Denver website. Please note there are occasional differences between the websites maintained by the city and the state and we recommend checking both.
Trish Zornio is a scientist, lecturer and writer who has worked at some of the nation’s top universities and hospitals. She’s an avid rock climber and was a 2020 candidate for the U.S. Senate in Colorado.