What are patient risk factors for a requirement of intensive care services in H1N1 influenza?
In the ANZIC study, infants (0 to 1 year of age), pregnant women, and adults 25 to 64 years of age appeared to be at particular risk for severe disease. Indigenous groups were overrepresented among patients who were admitted to ICUs: 10% in Australia and 25% in New Zealand. Further, both the ANZIC study and other studies indicate that obesity is a likely risk factor for increased severity of H1N1. In the ANZIC study, 29% of patients had a body-mass index (the weight in kilograms divided by the square of the height in meters) of 35 or more.
What is the risk of death after infection with the H1N1 influenza virus as compared to the risk of death after infection with seasonal influenza?
The proportion of patients who died in the ANZIC study (14%) is no higher than that previously reported among patients with seasonal influenza A who were admitted to an ICU. Patients admitted to an ICU with seasonal influenza A predominantly are elderly and have coexisting conditions. In H1N1, although older age, the presence of coexisting conditions, and a requirement for invasive ventilation were independently associated with increased risk of death in the ANZIC study, the majority of deaths occurred in younger patients because there were greater numbers of younger patients in the study cohort.
New England Journal of Medicine - Vol. 361, No. 20, November 12, 2009