The hospitalization rate in the USA between 15 April and 24 June 2009 was 2.21% with the highest rate of hospitalization being seen in people below 24 years. Most patients who required admission did so within 1-7 days, with a median of 4 days, from the onset of illness [31] . 73% of these patients had some underlying disease which predisposed them to a severe disease and complications. The most common underlying disorders were asthma (28%), neurological disorders (21%), diabetes (15%), immunosuppression (15%) and cardiovascular disorders (13%), with the others being chronic renal disorder, chronic obstructive pulmonary disorder and pregnancy. Obesity was found in 29% of the hospitalized patients with or without other risk factors. 25% of the hospitalized patients were critically ill [29] . Patients who required ICU admission, vasopressors, inhaled oxygen at FiO2 more than 60% or required mechanical ventilation were said to be critically ill [31] .