How long is a person with influenza contagious?

Duration of Influenza Contagiousness

Adults with influenza are contagious from 1 day before symptoms begin through approximately 5-6 days after symptom onset, while children remain infectious for up to 10 days after symptoms start. 1

Contagious Period by Population

Healthy Adults

• Infectious period extends from 1 day before symptom onset through 5-6 days after symptoms begin 2, 1
• Viral shedding decreases rapidly by 3-5 days after illness onset in most adults 1
• Most adults complete viral shedding by 5-7 days after illness onset 1
• Peak infectivity correlates with fever and respiratory symptoms 1

Children

• Children can be infectious for up to 10 days after symptom onset 2, 1
• Young children may shed virus several days before illness onset 1
• The extended infectious period in children necessitates longer isolation precautions compared to adults 1

Immunocompromised Patients

• Severely immunocompromised persons may shed virus for weeks or months 2, 1
• These patients require extended isolation precautions beyond standard recommendations 1
• Prolonged viral replication is especially common in patients receiving corticosteroid therapy or those with severe disease 1

Clinical Context

Incubation Period

• The incubation period ranges from 1-4 days, with an average of 2 days 2, 1
• This short incubation period explains why transmission can occur before individuals realize they are infected 1

Symptom Duration vs. Infectious Period

• Uncomplicated influenza typically resolves after 3-7 days 1
• Cough and malaise can persist for more than 2 weeks, but this does not indicate continued infectiousness 2, 1
• The infectious period ends well before symptom resolution in most cases 1

Practical Isolation Recommendations

For Adults

• Maintain isolation for at least 5-6 days after symptom onset 1
• Isolation can be discontinued after this period in immunocompetent adults, even if mild symptoms persist 1

For Children

• Maintain isolation for up to 10 days after symptom onset 1
• This longer duration accounts for prolonged viral shedding in pediatric populations 1

For Hospitalized Patients

• Implement Standard and Droplet Precautions until hospital discharge or until symptoms resolve and the patient has been afebrile for at least 24 hours 1
• For immunocompromised hospitalized patients, longer isolation periods are necessary due to prolonged viral shedding 1

Common Pitfalls

Do not confuse symptom duration with infectious period. Many patients continue to have cough and fatigue for 2+ weeks, but they are no longer contagious after the initial 5-6 days (adults) or 10 days (children) 2, 1. The amount of virus shed correlates directly with infectivity and transmission risk, which decreases rapidly after the first few days 1.

Do not apply adult isolation timelines to children. The pediatric infectious period is substantially longer, requiring extended precautions 1.

Do not underestimate viral shedding in immunocompromised patients. Standard isolation timelines do not apply to this population, who may require weeks of isolation 2, 1.