From the Guidelines
The flu is typically contagious for about 5-7 days after symptoms begin, though this period can vary, with adults usually being infectious from the day before symptoms start until approximately 5 days after illness onset, as stated in the most recent and highest quality study 1. When considering morbidity, mortality, and quality of life, it's crucial to understand the contagious period of influenza to implement effective preventive measures.
- The contagious period can vary among different groups, with children potentially being infectious for more than 10 days after the onset of symptoms and severely immunocompromised persons shedding virus for weeks or months 1.
- Most adults can spread the virus from the day before symptoms start until about 5-7 days after becoming sick, with the first 3-4 days of illness being the most contagious period when symptoms are usually most severe.
- To prevent transmission, staying home until being fever-free for at least 24 hours without using fever-reducing medications is recommended, along with practicing good hand hygiene, covering coughs and sneezes, and avoiding close contact with others while sick. The flu virus spreads through respiratory droplets when infected people cough, sneeze, or talk, and can also spread by touching contaminated surfaces, highlighting the importance of preventive measures to reduce the risk of transmission, as supported by the findings of 1.
From the Research
Duration of Contagiousness
- The mean duration of influenza virus shedding in immunocompetent adult patients is around 5 days, but may continue for up to 10 days or more, particularly in children, elderly adults, patients with chronic illnesses, and immunocompromised hosts 2.
- Influenza can be transmitted by sneezing and coughing via large particle droplets, as significant numbers of influenza virus particles are present in the respiratory secretions of infected persons 2.
Factors Affecting Contagiousness
- The duration of contagiousness may be affected by the initiation of antiviral treatment, with early commencement (<2 days from illness onset) associated with reduced morbidity and mortality 2.
- The use of antiviral medications, such as oseltamivir, can reduce the duration of influenza-related symptoms by approximately 1 day if initiated within 48 hours of the onset of symptoms 3, 4.
Symptoms and Transmission
- Influenza typically begins with the abrupt onset of high-grade fever, myalgia, headache, and malaise, accompanied by symptoms of respiratory tract illnesses such as nonproductive cough, sore throat, and nasal discharge 2, 5.
- The virus can be transmitted through respiratory secretions, and individuals at risk of influenza and related complications include older people, young children, and individuals with chronic renal, cardiac, and respiratory diseases 6.