What are the odds that someone is still contagious with COVID-19 (Coronavirus Disease 2019) 7 days after symptom onset and initial positive test, if they still have symptoms today?

COVID-19 Contagiousness 7 Days After Symptom Onset

A person who had COVID-19 symptoms and a positive test 7 days ago, and still has symptoms today with another positive test, has a high likelihood of remaining contagious. 1

Risk of Continued Infectiousness

• Contagiousness of SARS-CoV-2 typically lasts an average of 10 days from symptom onset in mild-moderate COVID-19 cases 1
• For immunocompromised patients or those with severe/critical COVID-19, contagiousness can be longer, extending up to 15 days 1
• Viral viability (indicating infectiousness) has been documented up to 20 days from symptom onset in some cases 1

Evidence from Testing and Viral Shedding Studies

• For patients tested more than 5 days after symptom onset, pooled sensitivity of antigen tests is approximately 80% (95% CI: 74% to 86%), indicating significant viral presence still detectable at this timeframe 1
• A positive antigen test at day 7 with ongoing symptoms strongly suggests continued viral replication and potential infectiousness 1
• A prospective community cohort study found that 65% of cases continued to shed infectious virus 5 days after symptom onset, and 24% were still shedding infectious virus 7 days after symptom onset 2

Factors Affecting Continued Contagiousness

• Persistent symptoms are a key indicator of potential ongoing infectiousness, especially when accompanied by positive test results 1
• The initial rate of viral replication appears to determine the course of infection and duration of infectiousness 2
• The median duration of the communicable period (defined as the interval from first positive test to first continuous negative tests) has been observed to be 9.5 days, but can extend up to 21 days in some cases 3

Clinical Implications

• The presence of both ongoing symptoms and a positive test at day 7 indicates that the individual has not yet cleared the infection 1
• Guidelines from infectious disease experts suggest that individuals with persistent symptoms beyond the typical isolation period may continue to pose transmission risk 1
• The combination of persistent symptoms and positive testing is more concerning for continued infectiousness than either factor alone 1

Common Pitfalls and Caveats

• PCR tests may remain positive for extended periods (up to 30 days) even after a person is no longer infectious, due to detection of non-viable viral fragments 1
• However, the presence of ongoing symptoms along with a positive test suggests active infection rather than just residual viral RNA 1
• Antigen tests correlate better with infectiousness than PCR tests, especially during the decline phase of infection (92% sensitivity for detecting infectious virus) 2
• Relying solely on time since symptom onset without considering ongoing symptoms and test results may lead to premature ending of isolation 1

Recommendations for Isolation

• Given the evidence of potential infectiousness at day 7 with ongoing symptoms and positive testing, continued isolation is warranted 1
• A symptoms-based approach suggests waiting until:
  1. At least 3 days (72 hours) have passed since recovery, defined as resolution of fever without fever-reducing medications 1
  2. Respiratory symptoms have shown clinically meaningful improvement 1
  3. At least 10 days have passed since symptoms first appeared 1