How long do you shed the influenza virus?

Influenza Viral Shedding Duration

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

Shedding Timeline by Population

Healthy Adults

• Infectious period begins 1 day before symptom onset and continues through day 5-6 after symptoms begin 2, 1
• Viral shedding peaks early and decreases rapidly by days 3-5 after illness onset 1
• Most adults complete viral shedding by days 5-7 after illness onset 1
• Research confirms that most viral shedding (the majority) occurs during the first 2-3 days after illness onset, with only 1-8% of infectiousness occurring before symptoms appear 3

Children

• Children remain infectious for up to 10 days after symptom onset 2, 1
• Young children can shed virus several days before illness onset 1
• Children under 5 years experience greater peak shedding, longer shedding durations, and more severe symptoms compared to other age groups 4

Immunocompromised Patients

• Severely immunocompromised persons may shed virus for weeks or months 1
• This population requires extended isolation precautions and potentially documentation of negative testing before discontinuing precautions 2
• Patients receiving corticosteroid therapy or those with severe disease may experience prolonged viral replication 1

Clinical Implications for Isolation

Standard Isolation Duration

• For hospitalized patients, maintain droplet precautions until hospital discharge OR until symptoms resolve AND patient has been afebrile for at least 24 hours 2
• For outpatient adults, isolation should continue for at least 5-6 days after symptom onset 1
• For children, maintain isolation for up to 10 days after symptom onset 1

Important Caveats

• The 24-hour afebrile rule may be insufficient, as research suggests shedding continues >24 hours post-fever resolution 5
• For immunocompromised patients in hospital settings, it is reasonable to maintain droplet precautions until hospital discharge or until documentation of negative H1N1 testing 2
• Most transmission occurs early in illness despite persistent viral shedding—approximately 63% of individuals shed <10% of their total virus before symptom onset 4

Transmission Risk Over Time

Peak Infectiousness

• The highest infectivity correlates with fever and respiratory symptoms, occurring in the first 2-3 days after symptom onset 1, 3
• Viral loads measured by RT-PCR decrease substantially after the first few days, though detectable virus may persist longer 3
• The amount of virus shed directly correlates with infectivity and transmission risk 1

Pre-symptomatic Transmission

• Patients become contagious 1 day before symptoms develop 2
• Only 1-8% of total infectiousness occurs during the pre-symptomatic period 3
• This finding suggests that "silent spreaders" may be less important in influenza epidemics than previously thought 3

Surface Contamination

• Influenza A remains viable on hard nonporous surfaces for 24-48 hours 2
• The virus persists less than 8-12 hours on porous materials like cloth or paper 2
• Dry virus particles can survive for 3 hours on human hands 2