Influenza (commonly called "the flu") is a contagious respiratory illness caused by influenza viruses. Infection with influenza viruses can result in illness ranging from mild to severe and life-threatening complications. An estimated 10% to 20% of U.S. residents get the flu each year: an average of 114,000 people are hospitalised for flu-related complications and 36,000 Americans die each year from complications of flu.
The main way that influenza viruses are spread is from person to person in respiratory droplets of coughs and sneezes. (This is called "droplet spread.") This can happen when droplets from a cough or sneeze of an infected person are propelled (generally up to 3 feet) through the air and deposited on the mouth or nose of people nearby. Though much less frequent, the viruses also can be spread when a person touches respiratory droplets on another person or an object and then touches their own mouth or nose (or someone else's mouth or nose) before washing their hands.
Scientific studies show that adults can shed virus from 1 day before developing symptoms to up to 7 days after getting sick. Young children can shed virus for longer than 7 days. In general, however, more virus is shed earlier in the illness than later.
If you start to develop cold symtoms but starting more rapidly and rather more violently, with higher fever and severe aches and pains, often in the back and muscles, then you may well be developing influenza. This may be associated with severe headache, cough, and, as a result of the fever, intermittent sweating and shivering. Sometimes there is a gastrointestinal element, with vomiting and/or diarrhoea.
Symptoms of flu include fever (usually high), headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches. Gastro-intestinal symptoms, such as...