H1N1 influenza: critical care aspects.

During the Northern Hemisphere spring of 2009, a novel H1N1 influenza A virus emerged in Mexico, causing widespread human infection and acute critical respiratory illness. The 2009 H1N1 virus spread initially to the United States and Canada, with subsequent rapid global dissemination, leading the World Health Organization (WHO) to declare "a public health emergency of international concern" in April 2009, and upgrading the viral threat to pandemic status in June 2009. Despite initial fears, the severity of the 2009 H1N1 pandemic overall did not differ significantly from that of seasonal influenza. However, the demographics of those at risk of severe illness did differ (affecting children and young adults, rather than the very young and the very old). The 2009 H1N1 pandemic led to rapid implementation of health care initiatives, including the provision of critical care services, to limit the effect of the influenza outbreak on the community. This review focuses on the critical care response to the H1N1 pandemic and examines whether the implementation of critical care services as planned a priori matched the reality of the clinical workload and the patient burden that transpired during the 2009 H1N1 influenza pandemic.