"Our analysis of critically ill patients with 2009 influenza A(H1N1) reveals that this disease affected a young patient group," the authors write. "Fever and respiratory symptoms were harbingers of disease in almost all cases. There was a relatively long period of illness prior to presentation to the hospital, followed by a short period of acute and severe respiratory deterioration."

By 60 days, 24 of the critically ill patients (41.4 percent) died. Nineteen patients died within the first two weeks after becoming critically ill.

"Patients who died had greater initial severity of illness, worse hypoxemia [abnormally low levels of oxygen in the blood], higher creatinine kinase levels, higher creatinine levels, and ongoing organ dysfunction," the authors report.

"Early recognition of disease by the consistent symptoms of fever and a respiratory illness during times of outbreak, with prompt medical attention including neuraminidase inhibitors and aggressive support of oxygenation failure and subsequent organ dysfunction, may provide opportunities to mitigate the progression of illness and mortality observed in Mexico," they conclude.

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