Nearly half of patients were children under the age of 18 and just 5 percent were over 65 in keeping with the theory that most elderly Americans may have some immunity to H1N1 due to prior exposure. Elderly patients were also less likely to experience severe illness, the CDC team noted. One positive note: "Patients seemed to benefit from antiviral therapy," the study authors wrote.
In the Australia/New Zealand report, researchers found that from June 1 through Aug. 31, 2009 -- winter in the Southern Hemisphere -- 722 patients with laboratory-confirmed H1N1 infections were admitted to intensive care units (ICUs) in those countries. This translates to 28.7 cases per million residents of the two nations.
Of these, 669 patients were under the age of 65 while 66 were pregnant women, another high-risk group.
Data on 601 patients showed that 172 had a body-mass index above 35, squarely in the obese category. And patients indigenous to both Australia and New Zealand were disproportionately hit.
Taken together, patients admitted to an ICU stayed there for a total of 8,815 "bed days," or 350 per million inhabitants. The average stay was seven days, ranging from 2.7 to 13.4 days.
Almost two-thirds of those hospitalized with the flu needed mechanical ventilation, and the average time spent on ventilation was eight days.
H1N1 patients took up a maximum of 7.4 beds per million inhabitants in a day in two countries that have 75 ICU beds for each million residents.
According to the report, "the greatest effect on ICU resources in a given region occurs approximately four to six weeks after the first confirmed winter ICU
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