What's in this article?
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses).
Influenza (flu) is a viral infection. People often use the term “flu” to describe any kind of mild illness, such as a cold or a stomach virus, that has symptoms like the flu. But the real flu is different. Flu symptoms are usually worse than a cold and last longer. The flu usually does not cause vomiting or diarrhea in adults.
Most flu outbreaks happen in late fall and winter. Because symptoms may not start for a couple of days, you may pass the flu to someone before you know you have it.
The flu is caused by influenza viruses A and B. There are different strains of the flu virus every year.
The flu causes a fever, body aches, a headache, a dry cough, and a sore or dry throat. You will probably feel tired and less hungry than usual. The symptoms usually are the worst for the first 3 or 4 days. But it can take 1 to 2 weeks to get completely better.
It usually takes 1 to 4 days to get symptoms of the flu after you have been around someone who has the virus.
Most people get better without problems. But sometimes the flu can lead to a bacterial infection, such as an ear infection, a sinus infection, or bronchitis. Less often, the flu may cause a more serious problem, such as pneumonia.
Certain people are at higher risk of problems from the flu. They include young children, pregnant women, older adults, and people with long-term illnesses or with impaired immune systems that make it hard to fight infection.
Influenza, or flu, is a respiratory illness that is caused by a virus. Flu is highly contagious and is usually spread by the coughs and sneezes of a person who is infected. 
You can also catch flu from an infected person if you touch them (e.g. shaking hands). Adults are contagious one day before getting symptoms and up to 7 days after becoming ill. This means that you can spread the influenza virus before you even know you are infected. A flu epidemic, when a large number of people in one country are infected with flu, can last several weeks.
According to the National Institutes of Health, between 5% and 20% of Americans get the flu each year. More than 200,000 people are hospitalized and 36,000 die annually because of flu in the United States.
What are the symptoms of flu?
It is common to confuse flu with a bad cold. Flu and cold symptoms may include a runny/blocked nose, sore throat, and cough. Here are some symptoms which a person with flu will have. These are not common heavy cold symptoms:
- high temperature
- cold sweats, shivers
- headache
- aching joints, aching limbs
- fatigue, feeling utterly exhausted
- gastro-intestinal symptoms, such as nausea, vomiting, and diarrhea, are much more common among children than adults
These symptoms may linger for about a week. The feeling of tiredness and gloom can continue for several weeks.
How serious is flu?
In the majority of cases flu is not serious – it is just unpleasant. For some people, however, there can be severe complications. This is more likely if you are elderly or have some other longstanding illness that can undermine your immune system. Your risk of experiencing severe flu complications is higher if:
- you are over 65
- you are a baby or a very young child
- you are pregnant
- you have some kind of heart or cardiovascular disease
- you have a chest problem, such as asthma or bronchitis
- you have a kidney disease
- you suffer from diabetes
- you are taking steroids
- you are undergoing treatment for cancer
- you have any longstanding disease that can significantly lower your immune system
How can it be prevented?
The best way to prevent influenza is to receive an influenza vaccination every year. The Centers for Disease Control and Prevention (CDC) recommends that everyone six months of age and older receive an annual vaccination. The best time to get vaccinated is in the early fall, as soon as the vaccine is available. However, vaccination throughout the flu season, even in January or later, is still beneficial. Seasonal flu outbreaks can happen as early as October, but most of the time flu activity peaks between December and February.
