Duration of positive covid test after infection
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Duration of Positive COVID-19 Test After Infection: RT-PCR and Antigen Test Insights
RT-PCR Test Positivity Duration After COVID-19 Infection
Research shows that the duration of a positive COVID-19 RT-PCR test after infection varies, but most studies report a median period of 15 to 20 days from symptom onset to a negative result. In a large study of 301 patients, the median time from symptom onset to a negative RT-PCR was 20 days, with older patients (≥65 years) remaining positive slightly longer than younger patients . Another study found the average time to transition from a positive to a negative PCR test was about 15 days, regardless of gender .
A systematic review of multiple studies found that the highest rate of virus detection from nasopharyngeal swabs occurred within the first 4 days after symptoms began, with detection rates dropping significantly after 10 to 14 days. In some cases, viral RNA was still detectable up to 46 days after symptom onset, though this was less common .
PCR Positivity Versus Infectivity
It is important to note that a positive PCR test does not always mean a person is still infectious. Studies have shown that while PCR tests can detect viral RNA for weeks after symptoms resolve, the ability to culture live virus (a sign of infectiousness) drops sharply after the first week of illness. Most patients are unlikely to be infectious beyond 8 to 10 days after symptom onset, even if their PCR test remains positive . This is because PCR can detect non-infectious viral fragments long after the active infection has ended .
Antigen Test Positivity and Infectious Period
Rapid antigen tests, which are more closely linked to the presence of viable virus, show that over half of people may still test positive 5 to 9 days after infection, but the percentage drops as more time passes. By day 10, most people test negative on antigen tests, suggesting a lower risk of being infectious .
Factors Affecting Duration of Positivity
The duration of positive test results can be influenced by several factors:
- Age: Older adults may remain positive longer .
- Sampling Site: Lower respiratory tract samples may remain positive longer than upper respiratory tract samples .
- Viral Load: People with lower initial viral loads (higher Ct values) tend to clear the virus faster .
- Vaccination and Previous Infection: Vaccinated individuals and those with prior infections are less likely to have prolonged positive antigen tests .
Persistent Symptoms and Long COVID
While most people clear the virus within 2 to 3 weeks, some may continue to experience symptoms for much longer. About 14% of people, including children, report persistent symptoms 15 weeks after infection, though this is not directly related to test positivity .
Conclusion
Most people with COVID-19 will test positive by RT-PCR for about 15 to 20 days after symptom onset, but this can vary based on age, sampling site, and initial viral load. PCR positivity can persist even after a person is no longer infectious, as live virus is rarely detected beyond 8 to 10 days after symptoms begin. Rapid antigen tests may provide a better indication of when a person is no longer infectious, with most people testing negative by day 10. Persistent symptoms can last much longer, but are not directly linked to test positivity.
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