Researchers in Hong Kong and the US found that the majority of viral shedding from sufferers of flu occurred during the first few days of symptomatic illness.
The study tracked 135 people with confirmed flu virus infection. Researchers assessed patients' viral shedding over the course of seven days and used molecular tests to identify flu strains.
They found that most viral shedding occurred during the first 2-3 days after illness onset.
The researchers estimated that just 1-8% of infectiousness occurred prior to illness onset.
Only 14% of infections with detectable shedding were asymptomatic, and viral shedding was low in these cases.