How long is someone contagious with COVID-19 (Coronavirus Disease 2019) after symptom onset?

Duration of COVID-19 Contagiousness After Symptom Onset

Most individuals with mild-to-moderate COVID-19 are contagious for approximately 10 days after symptom onset, though two-thirds remain infectious at day 5 and nearly one-quarter at day 7. 1

Infectious Window Timeline

The contagious period begins 1-2 days before symptoms appear, making pre-symptomatic transmission a critical feature of COVID-19 spread. 1 This distinguishes COVID-19 from many other respiratory infections and explains its rapid pandemic transmission. 1

Peak viral shedding occurs within the first 7 days of illness, with viral titers highest during this early phase. 1 Live virus remains detectable in the respiratory tract for up to 9 days in most individuals. 1

Duration by Disease Severity

Mild-to-Moderate Cases

• Median duration: 5 days after symptom onset, though this represents when half of patients are no longer infectious. 1
• Viral shedding continues for 1-2 weeks in most mild-moderate cases. 1
• By day 10, most patients are no longer infectious, with studies showing that COVID-19 patients with mild-to-moderate illness are highly unlikely to be infectious beyond 10 days of symptoms. 2
• Contact tracing studies found no evidence of transmission when close contacts were first exposed more than 5 days after symptom onset in the index case. 2

Severe-to-Critical Cases

• Viral shedding extends beyond 2 weeks in severe cases. 1
• Contagiousness can extend up to 15 days for those with severe/critical COVID-19. 1, 3
• Viral viability has been documented up to 20 days from symptom onset in some severe cases. 1, 3, 4
• In virus culture studies of severe/critical disease, SARS-CoV-2 was isolated up to day 32 in one study. 2

Immunocompromised Patients

• Prolonged viral shedding occurs, with quarantine extending to at least 20 or more days following symptom onset. 1
• Replication-competent virus isolated for up to 20 days in immunocompromised patients. 2
• Contagiousness can extend up to 15 days or longer in this population. 3

Practical Isolation Recommendations

For symptomatic patients with mild-moderate disease:

• Continue isolation until at least 10 days have passed since symptom onset. 1, 3
• Additionally, ensure at least 3 days have passed since recovery (defined as resolution of fever without fever-reducing medications and improvement in respiratory symptoms). 1, 3

For patients with persistent symptoms beyond day 7 and positive testing:

• Continue isolation, as this combination indicates active infection and potential infectiousness. 1, 3
• The presence of both ongoing symptoms and a positive test strongly suggests continued viral replication. 3

For immunocompromised or severe/critical cases:

• Extend isolation to at least 20 days following symptom onset. 1

Common Pitfalls

PCR testing limitations: 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. 3 However, ongoing symptoms combined with positive testing suggests active infection rather than just residual viral RNA. 3

Antigen testing correlation: Nucleocapsid (N) antigen testing is a strong predictor of viral infectiousness (relative risk=7.61 for culture positivity) and may be more suitable than viral RNA or symptom assessment alone for determining when to discontinue isolation within two weeks from symptom onset. 5

Asymptomatic transmission: Approximately 30-60% of patients shedding virus may have no symptoms, making asymptomatic transmission a significant concern throughout the infectious period. 1