Swine flu, also known as the H1N1 virus, has hit Australia accounting for the majority of influenza cases this year, health officials said Tuesday.The Influenza Specialist Group (ISG) said that Australia is experiencing double the number of cases compared to last year with more than 21,000 reported cases of influenza so far, Xinhua reported.Almost three quarters of the reported cases were of the H1N1 strain.ISG chairman Alan Hampson said all people, and not just the elderly, were suffering from the virus."People tend to think of the flu as an illness that has its worst impact on the elderly," Hampson said. "The reality is that influenza results in 18,000 hospitalisations every year. Many of those seriously affected are not elderly people they are regular working people," Hampson added.