Influenza, also known as the flu, is a disease caused by infection of the upper respiratory tract with the influenza virus. It is characterized mainly by sore throat, cough, and fever, and some patients may also experience nausea, vomiting, and diarrhea. The primary mode of transmission of influenza is through droplets, which occur when an infected person sneezes or coughs, and their secretions, such as nasal discharge, are inhaled by others. Additionally, the virus can be transmitted through the digestive tract and mucous membranes of the skin. If a healthy person comes into contact with the secretions of an infected person, such as through skin contact or orally, they may also be infected. Therefore, it is crucial to isolate from those infected with the flu.