Progression and impact of the first winter wave of the 2009 pandemic H1N1 influenza in New South Wales, Australia.

A range of surveillance systems were used to assess the progression and impact of the first wave of pandemic H1N1 influenza in New South Wales, Australia during the southern hemisphere winter. Surveillance methods included laboratory notifications, near real-time emergency department syndromic surveillance, ambulance despatch surveillance, death certificate surveillance and purpose-built web-based data systems to capture influenza clinic and intensive care unit activity. The epidemic lasted 10 weeks. By 31 August 2009, 1,214 people with pandemic H1N1 influenza infection were hospitalised (17.2 per 100,000 population), 225 were admitted to intensive care (3.2 per 100,000), and 48 died (0.7 per 100,000). Children aged 0-4 years had the highest hospitalisation rates, while adults aged 50-54 had the highest rates of intensive care admission. During the epidemic period, overall presentations to emergency departments were 6% higher than in 2008, while presentations for influenza-like illness were 736% higher. At the peak, confirmed cases of pandemic H1N1 influenza consumed 15% of intensive care capacity. Excess mortality from influenza and pneumonia was lower than in recent influenza seasons. Health services, particularly emergency departments and intensive care units, were substantially affected by the epidemic. Mortality from influenza was comparable with previous seasons.