2.1
Influenza is an acute infection of the respiratory tract caused by the influenza A and B viruses. The symptoms of influenza are fever accompanied by respiratory symptoms such as sneezing, coughing, runny nose and sore throat and systemic symptoms such as malaise, myalgia, chills and headaches. Gastrointestinal symptoms such as nausea, vomiting and diarrhoea are also common. Influenza infection is usually self-limiting and lasts for 3 to 4 days, with some symptoms persisting for 1 to 2 weeks. The severity of the illness can vary from asymptomatic infection to life-threatening complications. The most common complications are secondary bacterial infections such as otitis media, pneumonia and bronchitis.