With the Covid-19 pandemic still ongoing, testing remains an important tool for controlling the spread of the virus. Many people who test positive for Covid wonder how many negative tests they should receive before they can safely end isolation. Here is a quick look at the guidance on negative tests and ending isolation.
CDC Recommendations for Ending Isolation with Negative Tests
The CDC recommends the following for ending isolation if you had Covid-19 symptoms:
- At least 5 days since symptoms first appeared and
- At least 24 hours with no fever without fever-reducing medication and
- Other symptoms of COVID-19 are improving
If you meet those criteria, the CDC says you should take a COVID-19 test. If the test is negative, you can end isolation. However, you should continue to wear a well-fitting mask around others at home and in public until day 10. If you are unable to take a test or choose not to test, you can end isolation after 10 days if you are fever-free for 24 hours without medication and other symptoms have improved.
For those who test positive but never develop COVID-19 symptoms, the CDC recommends:
- Isolating for at least 5 days after the positive test and
- If you continue to have no symptoms, getting a negative test on day 5 or later and ending isolation
Alternatively, you can end isolation after 10 days if you continue to have no symptoms. Wearing a well-fitting mask around others at home and in public is recommended until day 10.
Why the CDC Recommends 1 Negative Test
The CDC’s criteria for ending isolation focus on a single negative test along with an improvement in symptoms and being fever-free. So why not require two or three negative tests before ending isolation?
There are a few reasons health experts say requiring just one negative test is appropriate in most cases:
- PCR tests can pick up small, non-infectious remnants of virus for weeks or longer after infection. A second or third test may still detect these remnants after you are no longer contagious.
- Requiring multiple tests creates difficulties with access to testing. Additional tests when not clinically necessary can tax limited supplies.
- For most people, the risk of transmission after 5+ days and 1 negative test is low, especially with masking.
Since PCR tests are so sensitive, there is no precise test-based threshold that guarantees a person is no longer infectious. The CDC determined that for asymptomatic people or those with mild illness, one negative PCR test plus 5+ days since onset provides reasonable evidence that shedding of infectious virus has decreased enough to safely end isolation.
When Might Additional Negative Tests Be Needed?
While one negative test is sufficient for many people, there are some situations where additional testing may be recommended or required:
- Severe illness: People who were hospitalized or have a weakened immune system may shed virus longer. Their doctors may recommend 2-3 tests spaced out over several days before ending isolation.
- Returning to high-risk settings: Healthcare workers and those in nursing homes may need 2+ negative tests before going back to work where transmission risks are higher.
- Travel requirements: Some destinations may require 2+ negative tests over a period of time before entering the country.
- Shortening 10-day isolation: Obtaining a negative test is necessary for most people to end isolation before 10 days per CDC guidelines.
Workplaces, schools, travel operators, and other organizations may also choose to implement more stringent testing policies before allowing people with COVID-19 to return versus CDC requirements. In these situations, the individual will need to follow those protocols.
Problems with Requiring Multiple Tests
While there are some cases where getting more than one negative COVID test may be prudent, there are also some downsides to requiring two or three universally:
- Each additional test increases costs for individuals or organizations.
- Frequent testing strains supplies of rapid tests and laboratory resources for PCR tests.
- Diminishing returns: Each test provides only marginally more assurance but takes another 1-2 days.
- Delayed returns to work and school, with cascading impacts on the community.
These impacts explain why most public health agencies have not deemed multiple tests necessary for ending isolation in low-risk cases. The potential downsides tend to outweigh the minimal additional risk reduction compared to a single test.
How Soon Should You Test After Exposure or Symptoms?
While most guidance focuses on negative tests to end isolation, testing also comes into play during the incubation period and early in the course of infection. The CDC offers the following testing guidance for unvaccinated people or those who are more than 6 months out from their last vaccine dose:
- After exposure: Get tested 5 days after exposure, or sooner if symptoms develop.
- After COVID-19 symptoms: Get tested immediately and isolate until results are received.
Proper timing is important when testing after exposure or at the onset of symptoms. There is no value in testing too early when the results are still likely to be negative. But equally, delaying enables more spread. Testing at the right interval balances practicality with preventing transmission.
How Long After Exposure Until You Test Positive?
If you have been exposed to COVID-19, how long might it take for a test to turn positive if you get infected? Here is the typical timeline:
- 1-3 days: Too soon for most tests to detect the virus.
- 3-5 days: PCR tests can usually detect the virus at this point.
- 5-7 days: Both PCR and rapid antigen tests will detect most infections.
- 7-10 days: Virtually all tests will detect COVID-19 if you are infected.
This demonstrates why the CDC suggests waiting 5 days after exposure before testing. Earlier than this, and a test risks being falsely reassuring. Beyond 5 days, and you have a good indication of whether you’ve been infected or not.
PCR vs. Rapid Antigen Testing
When considering the best timing for testing, it’s also important to factor in the type of test used. PCR tests that are sent to a laboratory are more sensitive than rapid antigen tests you can take at home or at testing sites.
PCR tests can often detect the virus 1-2 days sooner than rapid antigen tests when infected. This makes them a better choice right at the start of symptoms or after recent exposure. But by 5-7 days after exposure or symptom onset, antigen tests are nearly as accurate as PCR at identifying COVID-19.
Concerns Around Accuracy of COVID Tests
Some people harbor doubts about the accuracy of COVID-19 tests. However, both PCR and rapid antigen tests are considered highly reliable when used correctly and at the right time.
Here are assurances around COVID test accuracy to address common concerns:
- PCR tests are over 95% accurate for diagnosing COVID-19, often up to 98-99% sensitive.
- Rapid antigen tests are 80-90% accurate when used in the first week of COVID-19 illness.
- False positives are extremely rare with PCR and uncommon with antigen tests.
- Testing procedures include safeguards and controls to catch errors or sample mix-ups.
No test is 100% perfect. But when FDA-authorized COVID-19 tests are used as directed, you can trust a positive result. If there is uncertainty, repeat testing can provide more confirmation.
How Long After COVID Exposure Until No Longer Contagious?
If you may have been exposed to COVID-19 but never develop symptoms or test positive, how long until you can be confident you did not become infected and contagious? The CDC provides the following general guidance:
- After exposure, monitor for symptoms for 10 days.
- Consider taking a test at least 5 days after exposure.
- If you have no symptoms and test negative after 5 days, you can be confident you did not become infected.
- You may consider taking additional precautions like masking and distancing for the full 10 days after exposure.
With the incubation period of COVID-19 being 2-10 days, most people who caught the virus will start to show signs or test positive within 5 days of exposure. Continuing to monitor for symptoms and taking precautions for the full 10 days is still wise.
Shorter Contagious Period with Omicron?
Some emerging research suggests the Omicron variant may have a shorter contagious period compared to earlier versions of the COVID-19 virus. This shorter window could enable people to reasonably conclude they did not catch Omicron somewhat sooner than 10 days after exposure.
However, the data is still limited, and Omicron can be unpredictable. For now, the standard 10-day guidance remains a safer approach after potential exposure to Omicron.
Conclusion
Testing is a crucial tool for controlling COVID-19 transmission while balancing the need for people to work and go about daily activities. The CDC’s guidelines factor in the capabilities of different tests along with the dynamics of infection to arrive at reasonable recommendations.
In most cases, one negative PCR or antigen test along with improving symptoms and no fever is sufficient to safely end isolation after 5+ days. Additional tests may occasionally be warranted based on individual circumstances like travel or high-risk settings.
When testing after COVID-19 exposure or new symptoms, proper timing is key. But overall, FDA-authorized COVID-19 tests provide reliable results that people can trust, especially when used as directed.
