What is Influenza?

Influenza is a highly contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. According to most experts, the flu virus is mainly spread by droplets made when people infected with the flu cough, sneeze or talk. The flu may also be spread when someone touches a surface that had the flu virus on it, then proceeds to touch their own mouth, eyes or nose. This virus can cause mild to severe illness, and at times may lead to death. There are two main types of influenza virus: Types A and B. Influenza A viruses can be broken down into sub-types depending on the genes that make up the surface proteins. There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. Current subtypes of influenza A viruses found in people are influenza A (H1N1) and influenza A (H3N2). Influenza B viruses are not divided into subtypes, but can be further broken down into lineages and strains. Currently circulating influenza B viruses are B/Yamagata and B/Victoria, which are both lineages. Over the course of a flu season, different types of influenza A and B, along with numerous sub-types from influenza A, circulate and cause illness (Centers for Disease Control and Prevention, 2014).

When naming influenza viruses, the Center for Disease Control uses the following criteria: 

• The antigenic type
• Host of origin
• Geographical Origin
• Strain Number 
• Year of isolation
•  For influenza A viruses, the hemagglutinin and neuraminidase antigen description in parentheses (ex: H1N1)

Signs and Symptoms:

• Fever
• Cough
• Sore Throat
• Running or stuffy nose
• Muscle/body aches
• Headaches 
• Fatigue 
• Some may experience vomiting and diarrhea, but this is more common in children