What is Influenza (Flu)? Definition, Meaning, Facts, and Types

Definition and meaning

Influenza, or flu as it is also called, is defined as an extremely common and contagious febrile infection of viral origin (meaning caused by a virus) infecting the mucous membrane of the upper respiratory tract and sometimes the lungs. The upper respiratory tract includes the nose, the throat, and the bronchi.

Fever, cough, and cold are the classical symptoms, which accompany this viral infection.

Being of viral origin, it is usually self-limiting, but may require a little aggressive treatment if there is super added bacterial infection, otherwise, mild treatment may be given for symptomatic relief.

Flu Duration: How long does the flu fever last?

The following quote aptly describes the lifespan of flu:

“If the doctor gives you treatment for flu, it will go away in seven to fourteen days, and if you leave the flu alone, it will go away in one to two weeks”.

Though the above fact does indicate that flu is self limiting and not a serious disease or illness, certain complications can occur which can be fatal. The death rate of this disease is about 0.1 percent. It should, therefore, never be ignored.

The symptoms are worst during the first two to three days of the fever and usually last for 7 to 8 days. Some symptoms like weakness and cough can persist for 2 to 3 weeks. All this depends much on your overall health and the condition of your immune system. Healthy people who have a strong immunity will recover earlier.

According to the Center For Disease Control and Prevention:

“While the numbers vary, in the United States, millions of people are sickened, hundreds of thousands are hospitalized and thousands or tens of thousands of people die from flu every year”

According to the National Institute of Allergy and Infectious Diseases, children are three times more likely to get infected with this disease than healthy adults.

Please note that influenza is not the same as the stomach flu, which is also caused by a virus, symptoms including diarrhea and vomiting.

Facts about Flu

  • Influenza or flu is contagious and easily spreads from person to person.
  • It is present worldwide
  • It can infect any age group.
  • It can cause epidemics, which have turned into pandemics.
  • These epidemics or outbreaks are seen more during the cold climates.
  • Though flu is a moderately severe illness, it can cause dangerous complications in young children under 5 years of age , and more so in those under 2 years
  • Elderly people above the age of 65 years are also more prone to suffer from complications because of lowered immunity.
  • Along with pneumonia (which can be a complication), influenza is the eighth leading cause of death in America.
  • According to  The Centers for Disease Control and Prevention (CDC), about 5% to 20% of the U.S. population on an average gets the flu every year – that is about 35 to 50 million people.
  • The flu season typically lasts from October to March in the United States.
  • In the United States, about 2,00,000 people are admitted to hospital for flu every year and about 36,000 people die from its complications every year.
  • You can catch this infection more than once because there are many strains of the flu virus, which keep on mutating, and each of them can cause an infection. Developing immunity against some strains of this virus, therefore, is difficult.
  • Getting vaccinated is the most effective way to prevent you from getting infected by the flu virus. Vaccinations are indicated every year and for everybody above the age of six months. In the United States, the flu vaccine is given in the month of October.
  • Influenza and cold are different. Though cold may be a symptom of influenza, it is a rather subdued form, while influenza can make you stay in bed for a week or more.

Types of Flu

Influenza or flu is classified according to its severity, which is related to the kind of the virus that has caused the infection. It is caused by the flu virus, which is an RNA (ribonucleic acid) virus. This causative agent, which is the main culprit that gives you the flu, is of three diffeent types:

  1. Influenza virus A
  2. Influenza virus B and
  3. Influenza virus C

All these viruses can give you the infection, but type A virus is the most common cause of the flu sickness and of epidemics, followed by the type B virus. Flu caused by the Type C virus is not severe.

Type A Flu Virus

As mentioned above, this is the most commonly seen flu virus and also the most common cause flu epidemics. Though it is more common for humans to be infected by this type of flu, animals like swine are also seen to be infected and birds such as poultry act as carriers of this flu.

This virus is constantly mutating and therefore newer vaccines and drugs are required to control this virus, which has several serotypes (distinct variations). Bird flu and swine flu are caused by this virus.

The type A virus spreads through the air and also via the surfaces of the objects which, have been contaminated by the infected person.

Such objects may be bank notes, door knobs, telephones, household utensils, computer keyboards light switches, and other such commonly touched items. Linens such as handkerchiefs are also potential residents for this type of virus.

Type B Flu Virus

Unlike the type A virus, the Type B flu virus is seen to infect only humans. It can also cause epidemics but the severity of disease caused by this virus is limited. It mutates more slowly and has only one serotype and therefore immunity against this virus develops early on in life.

Type C flu Virus

This is the least commonly seen among the influenza viruses. Its infective virility is quite low and is seen to cause mild infections in children only. It is not related to the flu season or the seasonal flu. However, it is seen to cause epidemics in dogs and pigs but not in humans. The yearly flu vaccine does not offer protection against C viruses.

What is the seasonal flu?

Seasonal flu refers to the outbreaks that occur mainly in the late fall and winter each year.

The disease can spread through communities, which can lead to an epidemic. During the epidemic, the number of people affected peaks in about three weeks and subsides after another three to four weeks.

What is the Pandemic Flu?

Pandemic flu refers to the spread of flu rapidly from person to person to create a worldwide epidemic (pandemic). It is caused by the contagious strains of the flu virus. Influenza pandemics were seen in 1918, 1957, 1968, and 2009.

 

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