How long is an immunocompetent adult infectious after a positive COVID-19 test?

Duration of Contagiousness After Testing Positive for COVID-19

For immunocompetent adults with COVID-19, you are most contagious from 1 day before symptom onset through 2-3 days after, with peak infectiousness occurring around day 4 of symptoms, and live virus is generally not detectable after 8 days from symptom onset—meaning most people are no longer infectious after 10 days. 1, 2

Peak Infectiousness Timeline

• Peak viral shedding and maximum contagiousness occurs around day 4 of symptoms 2
• Approximately 40% of transmissions occur before symptoms develop (presymptomatic transmission) 1
• Peak infectiousness spans from 1 day before symptom onset until 2-3 days after symptom onset in typical individuals 1

Duration of Viable Virus (Actual Infectiousness)

• Live, infectious SARS-CoV-2 virus is not detectable after 8 days from symptom onset in uncomplicated cases, even when PCR tests remain positive 1, 2
• Most adults have replication-competent virus for 10-14 days after symptom onset, with the majority clearing infectious virus by day 10 3
• Median time from symptom onset to negative viral culture is 11 days 3

Critical Distinction: PCR Positivity vs. Infectiousness

PCR tests can remain positive for up to 30 days after initial infection, but this does NOT mean you are still contagious. 1, 2 This is a crucial pitfall to avoid:

• PCR detects viral RNA fragments (dead virus pieces), not live virus 1, 2
• Requiring negative PCR before ending isolation leads to unnecessarily prolonged delays and should not be done 1, 2
• Half of patients still test PCR-positive 21-30 days after symptom onset, long after they are infectious 2

Practical Isolation Recommendations

Use a symptom-based approach, NOT repeat PCR testing: 1, 2

• End isolation after 10 days from symptom onset if symptoms are improving 1
• Minimum 3 days symptom-free before ending isolation 1
• No fever for ≥24 hours without fever-reducing medications 4

Early Isolation Release (5-9 Days)

Rapid antigen tests (NOT PCR) can guide earlier release from isolation: 4, 3

• Nucleocapsid (N) antigen testing strongly predicts infectiousness (relative risk of culture positivity = 7.66 if N antigen positive) 3
• After 5-9 days, 54.3% of people still test antigen-positive, indicating ongoing infectiousness 4
• Negative N antigen test is a suitable biomarker to discontinue isolation within 2 weeks from symptom onset 3

Special Populations Requiring Longer Isolation

Severe/Critical COVID-19

• Symptom duration can exceed 2 weeks in approximately 20% of cases 1
• Viral viability documented up to 20 days from symptom onset in severe cases, though this is exceptional 2
• Consider extending isolation to 15-20 days based on clinical status 2

Immunocompromised Patients

• May experience prolonged viral shedding beyond 3 weeks from initial positivity 2
• Isolation may need to extend to 20+ days following symptom onset due to genuinely prolonged viral shedding 2
• Individualized decisions with infectious disease consultation recommended for persistent positivity 2

Factors Affecting Contagiousness Duration

You are MORE likely to remain infectious longer if: 4

• Symptomatic infection (aOR = 9.63 for positive antigen test at 5-9 days) 4
• Earlier in the disease course (5 days vs. 9 days: aOR = 6.39) 4
• Unvaccinated (vaccination reduces duration: aOR = 0.60) 4

You are LESS likely to remain infectious if: 4

• Previously infected (aOR = 0.30) 4
• Both vaccinated AND previously infected (aOR = 0.17) 4

Post-Isolation Precautions

Even after ending isolation, continue wearing a well-fitting mask around others through day 10, as some individuals may remain infectious 4