Influenza is an acute infection of the respiratory tract caused by the influenza virus.
In the northern hemisphere, influenza is generally prevalent between November and April. In the southern hemisphere, the virus strikes between May and October. It may cause epidemics and worldwide pandemics. However, certain groups of patients are at particularly high risk from an attack of influenza. Watching for the First Signs Visual Library Glossary Spread of infection Infection with the influenza virus is most common in the winter months when people with acute infections spread the virus to other people by talking, coughing, or sneezing and produce tiny droplets that carry the virus through the air.