How long after testing positive for influenza are you no longer contagious?

Duration of Influenza Contagiousness After Testing Positive

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

Standard Infectious Period by Age Group

Adults

• Most adults are no longer contagious by 5-6 days after symptom onset, with viral shedding decreasing rapidly by days 3-5 in the majority of cases 1
• The infectious period begins approximately 24 hours before symptoms appear and extends through the fifth to sixth day after symptom onset 1
• Most adults complete viral shedding by 5-7 days after illness onset, though this represents when detectable virus is present rather than when transmission risk ends 1

Children

• Children remain infectious for a longer duration—up to 10 days after symptom onset—and may even shed virus several days before illness begins 1
• Young children can shed virus before symptoms appear, making them particularly effective transmitters in household and school settings 1
• The extended infectious period in children necessitates longer isolation precautions compared to adults 1

Special Populations with Prolonged Contagiousness

Immunocompromised Patients

• Severely immunocompromised individuals may shed virus for weeks to months, requiring extended isolation precautions well beyond the standard timeframes 1
• Solid organ transplant recipients and other immunosuppressed patients can be contagious for 10 or more days, and isolation should continue until hospital discharge or documentation of negative testing 1
• For hospitalized immunocompromised patients, consider maintaining droplet precautions until hospital discharge or until negative H1N1 testing is documented 2, 1

Patients with Severe Disease

• Those with severe influenza, extensive pneumonia, respiratory failure, or acute respiratory distress syndrome may experience prolonged viral replication 2
• Patients receiving corticosteroid therapy or those with chronic cardiopulmonary conditions may have extended infectious periods 1

Clinical Implications for Isolation

Healthcare Settings

• In acute-care facilities, personnel with influenza-like illness should be removed from direct patient contact duties, with more stringent criteria applied for those working in intensive care units, nurseries, and transplant units 2
• For hospitalized patients, isolation using Standard and Droplet Precautions should continue until hospital discharge or until symptoms resolve and the patient has been afebrile for at least 24 hours 2, 1

General Population

• Isolation measures should continue for at least 5-6 days after symptom onset in adults and up to 10 days in children 1
• The highest infectivity correlates with fever and respiratory symptoms, particularly during the first 3-5 days of illness 1
• Even after the infectious period ends, cough and malaise can persist for more than 2 weeks, though transmission risk is minimal at this stage 1

Important Caveats

Timing Considerations

• The incubation period averages 2 days (range 1-4 days), meaning exposure to a positive case requires monitoring for this duration before symptoms would appear 1, 3
• Contagiousness begins before symptom onset, making it impossible to prevent all transmission through isolation of symptomatic individuals alone 1

Antiviral Treatment Impact

• To reduce transmission of drug-resistant virus, avoid contact between high-risk individuals and patients taking antivirals for treatment during therapy and for 2 days after discontinuation 2
• Early treatment with neuraminidase inhibitors (within 24-48 hours of symptom onset) may reduce duration of viral shedding, though the primary benefit is reducing symptom duration by approximately 24 hours 2, 4

Testing Limitations

• A positive influenza test confirms infection but does not indicate where the patient is in their infectious period—clinical assessment of symptom onset timing is essential 1
• For patients with recent flu-like symptoms, the relatively short duration of positive assays (often 5-7 days or less from symptom onset) should be considered when screening 2