Influenza transmission

Spread of infection occurs commonly through large virus containing droplets and aerosols (through coughing, sneezing or talking) and by indirect spread from respiratory secretions on hands, tissues, etc (1,2).

Less commonly it may spread through contaminated fomites. Children play an important role in the spread of the disease within communities and households:

• an outbreak of influenza amongst school children can herald the start of influenza activity in a community
• in some community outbreaks, the illness rates have been shown to rise and decline earlier in school children than in adults (1)

The level of virus shedding is at its lowest before the symptoms starts and continues for 5–10 days after illness onset (peak virus shedding is seen 1 day before onset of symptoms to 3 days after onset) (1).

• In young children virus shedding may last for a longer period than in adults.

Few patients may catch the infection and pass it on without showing any symptoms (or with very mild symptoms) (2).

References:

1. World Health Organization (WHO). WHO Global Influenza Surveillance Network. Manual for the laboratory diagnosis and virological surveillance of influenza
2. European Centre for Disease Prevention and Control (ECDC). Factsheet for professionals on seasonal influenza