From the Guidelines
If you have a persistently positive COVID-19 antigen test after 19 days, you can generally end isolation if you've been fever-free for at least 24 hours without fever-reducing medication and your other symptoms are improving. Most people are not contagious after 10 days, even with a positive antigen test 1. The CDC no longer recommends using test results to determine when to end isolation, as antigen tests can remain positive for weeks after infection despite the person no longer being infectious. This happens because the test detects viral protein fragments that remain in your body even after you're no longer contagious.
Key Considerations
- If you're immunocompromised or had severe COVID-19, consult your healthcare provider as you may need to isolate longer 1.
- While isolating, wear a high-quality mask around others, avoid contact with vulnerable individuals, and maintain good hand hygiene.
- Remember that a positive test after the acute infection period usually doesn't mean you're still contagious, but rather reflects the test's inability to distinguish between active virus and non-infectious viral remnants 1.
Testing and Isolation Guidance
- The Infectious Diseases Society of America (IDSA) suggests using standard NAAT over rapid Ag tests due to higher sensitivity, thus reducing the risk of missing a diagnosis of SARS-CoV-2 infection 1.
- For asymptomatic individuals with known exposure to SARS-CoV-2 infection, the IDSA panel suggests using a single standard NAAT over a single rapid Ag test 1.
- The IDSA panel also suggests neither for nor against 2 consecutive Ag tests over no testing for the diagnosis of SARS-CoV-2 infection in certain settings due to lack of evidence 1.
From the Research
Guidelines for Persistently Positive Antigen Test
- The guidelines for someone with a persistently positive Covid antigen test after 19 days are not explicitly stated, but studies suggest that isolation may be necessary for a longer period than initially recommended 2, 3.
- A study published in MMWR found that 54.3% of individuals still had a positive antigen test result after 5-9 days, with a declining percentage over time 2.
- Another study published in Microbiology spectrum found that infectious viruses could be isolated from nasopharynx samples up to 128 days after symptom onset, suggesting a potential risk of prolonged transmission 3.
- The use of rapid antigen tests to guide isolation recommendations is being explored, with studies suggesting that a negative test result may not always indicate the end of infectiousness 4, 5.
- Factors such as the detection limit of antigen tests, symptom presence, and an acceptable level of releasing infectious patients should be considered when designing isolation guidelines 5.
Key Considerations
- The risk of prolonged transmission from individuals with persistently positive antigen test results is a concern, particularly in settings where vulnerable individuals may be exposed 3.
- The use of serial testing with lateral flow devices may be an effective method of case ascertainment and reducing onward transmission 6.
- Isolation guidelines should be designed to minimize the risk of releasing infectious patients and the burden of redundant isolation of noninfectious patients 4, 5.