Influenza is a contagious respiratory illness caused by influenza viruses. Unlike the common cold, which can be triggered by over 200 different viruses, influenza is primarily caused by a handful of viral strains that belong to the Orthomyxoviridae family. The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses. What causes the flu? Seasonal influenza (the flu) is an acute respiratory infection caused by influenza viruses. It is common in all parts of the world. Most people recover without treatment. Influenza spreads easily between people when they cough or sneeze. Vaccination is the best way to prevent the disease. Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four (typically two) days after exposure to the virus and last for about two to eight days. There are four types of the influenza virus (A, B, C and D) — influenza A and B cause seasonal epidemics every winter, per the CDC. The predominant strains that circulate in the U.S. are H1N1. NHS information about flu, including symptoms, how to treat it yourself and when to get help. Flu cases have reached a 25-year high in the US, driven by a mutated H3N2 subclade K strain. CDC data shows record doctor visits for flu symptoms. Experts warn immunity gaps are worsening outbreaks, with unusual symptoms like vomiting yellow bile emerging, especially affecting older and high-risk populations. Read on. , Health News News, Health and Me Flu, also called influenza, is an infection of the nose, throat and lungs, which are part of the respiratory system. The flu is caused by a virus. Influenza viruses are different from the stomach flu viruses that cause diarrhea and vomiting. Most people with the flu get better on their own. What is the flu (influenza)? The flu is an illness you get from the influenza virus. It causes symptoms like head and body aches, sore throat, fever and respiratory symptoms, which can be severe. Flu is most common in winter months, when many people can get sick at once (an epidemic). Influenza (flu) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. Learn about flu, including symptoms, prevention methods, and treatment options.