How many days is a healthy adult contagious after influenza symptom onset, and how does this duration differ for children, elderly, immunocompromised individuals, or those receiving antiviral therapy?

How Long You're Contagious After the Flu

Healthy adults with influenza are contagious from 1 day before symptoms begin through 5-6 days after symptom onset, while children remain infectious for up to 10 days, and immunocompromised individuals may shed virus for weeks to months. 1

Contagious Period by Population

Healthy Adults

• Adults are infectious starting 1 day before symptoms appear and continuing through days 5-6 after symptom onset 1
• Viral shedding decreases rapidly by days 3-5 after illness begins in most adults 1
• Most adults complete viral shedding by days 5-7 after illness onset 1
• The highest infectivity occurs when fever and respiratory symptoms are most prominent 1

Children

• Children can be infectious before symptoms begin and remain contagious for up to 10 days after symptom onset 2, 1
• Young children may shed virus several days before illness onset 1
• Isolation should be maintained for the full 10 days in children 1

Immunocompromised Individuals

• Severely immunocompromised persons may shed virus for weeks or months 1
• This includes solid organ transplant recipients and those with severe immunodeficiency 1
• Extended isolation precautions are necessary, potentially until hospital discharge or documentation of negative testing 1
• Patients with chronic cardiopulmonary or neuromuscular conditions may also experience prolonged viral shedding 1

Elderly Patients

• While specific data for elderly patients is limited in the guidelines, those with underlying chronic conditions (common in this age group) may experience prolonged symptoms and viral shedding similar to other high-risk populations 1

Effect of Antiviral Therapy

• Early treatment with neuraminidase inhibitors (within 24-48 hours of symptom onset) may reduce the duration of viral shedding, though the primary benefit is reducing symptom duration by approximately 24 hours 1
• To reduce transmission of drug-resistant virus, avoid contact between high-risk individuals and patients taking antivirals during therapy and for 2 days after discontinuation 1
• Antiviral treatment does not eliminate the need for standard isolation precautions during the typical contagious period 1

Clinical Implications for Isolation

Standard Recommendations

• Isolation measures should continue for at least 5-6 days after symptom onset in adults 1
• For children, isolation should be maintained for up to 10 days after symptom onset 1
• For hospitalized patients, Standard and Droplet Precautions should continue until hospital discharge or until symptoms resolve and the patient has been afebrile for at least 24 hours 1

Special Populations

• For immunocompromised patients, longer isolation periods are necessary, potentially until hospital discharge or negative testing 1
• Healthcare personnel with influenza-like illness should be removed from direct patient contact, with more stringent criteria for those working in intensive care units, nurseries, and transplant units 1

Important Caveats

• Some infected individuals remain asymptomatic yet contagious throughout their infection 2
• Cough and malaise can persist for more than 2 weeks even after the infectious period ends, but this does not indicate ongoing contagiousness 1
• The amount of virus shed correlates with infectivity and transmission risk 1
• Influenza virus can survive on hard surfaces for 24-48 hours, on porous materials for 8-12 hours, and on human hands for up to 3 hours, highlighting the importance of hygiene measures beyond the person-to-person transmission period 1