Influenza A ( H1 N1 ) virus is the subtype of influenza A virus that was the most common cause of human influenza (flu) in 2009, and is associated with the 1918 outbreak known as the Spanish Flu .
Respiratory transmission occurs mainly by droplets disseminated by
unprotected coughs and sneezes. Short-distance airborne transmission of
influenza viruses may occur, particularly in crowded enclosed spaces. Hand
contamination and direct inoculation of virus is another possible source of