Seasonal and pandemic influenza virus infections cause substantial mortality and morbidity. At least 18 500 confirmed deaths occurred in the first year of the 2009 H1N1 influenza A pandemic, but modeling estimates suggest that over 200 000 respiratory deaths and an additional 85 000 cardiovascular deaths occurred worldwide, with the majority in Africa and Southeast Asia.1 Like most infectious diseases, influenza virus morbidity and mortality are skewed toward the very young ( < 2 years), the elderly ( > 65 years) and pregnant women, conditions in which key elements of the immune system necessary to curtail influenza are compromised.Influenza is contracted through inhaled aerosol droplets of infectious virus spread from infected individuals. Not unexpectedly, severe disease is more common among persons with underlying medical conditions that limit physiologic reserve, particularly as related to the lungs and cardiovascular system.
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