COVID-19 Rapid Tests Show Low Sensitivity During Omicron Surge

A recent study published in the Morbidity and Mortality Weekly Report reveals that COVID-19 rapid antigen tests (RATs) have a sensitivity of only 47% compared to reverse transcription polymerase chain reaction (RT-PCR) tests during the Omicron variant predominance. The findings, based on research led by the US Centers for Disease Control and Prevention (CDC) and Vanderbilt University, suggest that clinicians should consider using RT-PCR tests for high-risk patients eligible for antiviral drugs.

Why this matters: The accuracy of COVID-19 tests has a direct impact on the effectiveness of treatment and prevention strategies, making it essential to understand the limitations ofrapid antigen tests. This study's findings could influence public health policy and clinical guidelines, ultimately affecting the spread of the virus and the health of vulnerable populations.

The study compared the results of SARS-CoV-2 RATs and same-day RT-PCR and viral culture among 354 participants in a household virus transmission study. The researchers found that RAT sensitivity was 47% (95% CI: 44-50) compared to RT-PCR and 80% (95% CI: 76-85) versus viral culture. The proportion of positive RAT results peaked 3 days after symptom onset, while RT-PCR results peaked 2 days after onset.

The study authors noted, "The low sensitivity of antigen testing among persons with asymptomatic infections indicates that these tests should only be used once symptoms are present." They also found that RAT sensitivity rose with the occurrence of any COVID-19 symptom (56% vs. RT-PCR and 85% vs. culture) and peaked on days when fever was reported (77% vs. RT-PCR and 94% vs. culture).

The implications of these findings are significant for clinical practice. Clinicians should be aware of the lower sensitivity of antigen testing compared to RT-PCR, which might lead to false negative results. This is particularly important for the timely initiation of SARS-CoV-2 antiviral treatment. The researchers advised, "Clinicians should consider RT-PCR for persons for whom antiviral treatment is recommended." If RT-PCR tests are not available or accessible, clinicians and patients should follow the FDA's serial antigen testing recommendations to help optimize diagnostic test performance.

The study was conducted from November 2022 to May 2023 and included participants aged 2 months to 83 years, with a median age of 36 years. Participants completed daily symptom diaries and collected two nasal swabs for 10 days. Only one commercially available RAT was used in the study.

The findings also have implications for public health measures and outbreak control. With the lower sensitivity of RATs, relying solely on these tests for screening purposes may lead to undetected cases and further transmission. Combining RATs with RT-PCR testing, especially for high-risk individuals or in settings with high transmission rates, can help improve case detection and prevent outbreaks.

The global community continues to struggle with the challenges posed by the COVID-19 pandemic, studies like this one provide valuable insights into the performance of diagnostic tests and guide clinical decision-making. Healthcare providers can optimize patient care and contribute to the ongoing efforts to control the spread of the virus by staying informed and adaptingtesting strategiesbased on the latest evidence.

Key Takeaways

• Rapid antigen tests (RATs) have a sensitivity of only 47% compared to RT-PCR tests during Omicron variant predominance.
• RATs should only be used once symptoms are present, as sensitivity is low for asymptomatic infections.
• Clinicians should consider using RT-PCR tests for high-risk patients eligible for antiviral treatment.
• RAT sensitivity peaks 3 days after symptom onset, while RT-PCR results peak 2 days after onset.
• Combining RATs with RT-PCR testing can improve case detection and prevent outbreaks, especially in high-risk settings.