Influenza(Flu): Types, Symptoms, Causes, Risks, Complications, Diagnosis, Treatment and Prevention

A womem in bed who suffer from Influenza symtoms.


Many children and adults experience flu, an illness caused by a virus. Flu or influenza is a viral infection that targets the respiratory system, specifically the throat, nose, and lungs. For healthy individuals, having flu is not a big deal since it resolves on its own. However, this condition may become life-threatening for individuals who are at a higher risk of experiencing the complications of flu like pregnant women, children, older adults and those with weakened immune systems.

Seasonal influenza or flu is highly contagious and can spread easily from person to person. This type of virus circulates across the globe. It’s now considered a serious health concern and vaccinations are recommended to avoid the serious complications associated with this viral infection.

Flu can spread through infected people who cough or sneeze, which temporarily contaminate the air and surfaces. The infected droplets can stay on surfaces for hours.
The transmission of the disease can be prevented by practicing good hand and respiratory hygiene like covering the nose or mouth when coughing or sneezing.

The U.S. Centers for Disease Control and Prevention (CDC) reports that flu epidemics during the winter affect about 300,000 to 600,000 people every year. Out of this number, about 200,000 are hospitalized and about 3,000 to 49,000 die from the complications of the illness.

2Types of Influenza Viruses

There are three types of influenza viruses – A, B and C.

Influenza Type A

This type of influenza virus is classified into two subtypes – haemagglutinin (H) and neuraminidase (N), which are two proteins. This type of virus is the one responsible for the various outbreaks of the AH1N1 and AH3N2 infections. This virus has been linked to pandemics.

Influenza Type B

The influenza type B virus is known to cause outbreaks and epidemics.

Influenza Type C

This type of virus is detected less frequently. It causes only mild infections, which makes it less reported.


At the beginning of the illness, some people mistake influenza as just a common cold. However, common colds develop slowly but flu may begin abruptly. The most common symptom of influenza is fever, which is not present in people with a common cold.
Fever is the body’s defense against infection. When a person has a fever, this means that the body’s immune system is working against an infection.

Here are the common signs and symptoms of influenza or flu:

  • Fever, usually over 38 C or 100.4 F
  • Chills
  • Sweating Headache
  • Body pains and fatigue
  • Nasal congestion or a runny nose
  • Sore throat
  • Persistent dry cough

Most individuals with flu recover on their own without treatment. For people with mild cases of influenza, they should stay at home and as much as possible, avoid contact with other people, especially those who are vulnerable to the disease.


The cause of influenza or flu is a virus. The viruses Type A, B, and C cause respiratory syndromes that can cause flu. Aside from humans, the influenza virus B only affect people.

Flu viruses spread mainly by droplets in the air when people a cough, talk or sneeze.
Aside from being suspended in the air, these droplets may land in the noses or mouths of people who are near. Moreover, the droplets can stay on surfaces like telephone receivers, tables, and door knobs. If the person came in contact with these droplets and he or she touched the mouth, eyes or nose, the infection may occur.

The period of contagiousness is between one day before the symptoms appear and seven days after becoming sick. Young kids and those with weakened immune systems can even infect other people for an even longer time.

The bad thing about this virus is that it’s constantly changing and mutating. New strains appear from time to time. This means that the body can have antibodies to target the flu virus specifically, but if you had influenza in the past, this might not be the same strain that infected you now.

The body’s antibodies against flu viruses you had in the past are unable to protect you from a new influenza strain or subtype.

Why is influenza more common during the winter season? This is because the virus can live longer indoors during the winter. The air inside the house is less humid and people stay indoors more because of the cold climate. People spend more time in the house and have closer contact with other family members.

5Risk Factors

There are many risk factors associated with influenza. While anyone can get infected with the virus, some people are at a higher risk of complications of the infection.

Those who are at risk of complications are:

  • Children and infants who are under five years old. Children who are below two years old are more prone to complications.
  • Adults who are 65 years old and above
  • Pregnant women
  • Women who have just given birth in the last two weeks
  • People living in long-term care facilities like nursing homes
  • People who have compromised or weakened immune systems
  • People who are living with chronic diseases such as kidney disease, diabetes, heart disease and asthma.
  • People who are morbidly obese – with BMI of 40 or higher.

Moreover, people who have certain medical conditions are at a higher risk of developing complications of influenza like:


The complications of flu mostly affect people who belong to high-risk groups. Hence, vaccinations are important for these individuals. For healthy individuals, acquiring the seasonal flu is not serious. However, for those who are at a higher risk, here are the possible complications associated with influenza.

Chest infections and Pneumonia

The most common complication of flu is a bacterial chest infection like bronchitis and pneumonia. Pneumonia is the most serious and potentially-fatal complication of the flu.

Worsening of underlying conditions

People with the long-term condition who get the flu needs to be checked for certain complications. For instance, people with asthma or COPD may find their symptoms more severe when they acquire the flu virus.

Also, those with diabetes and other conditions that affect blood sugar levels, the virus can cause an increase in blood sugar, called hyperglycemia. This may lead to a serious complication dubbed as diabetic ketoacidosis, which is caused by the lack of insulin in the body.

Complications during pregnancy

For pregnant women, getting the flu may increase the risk of pregnancy problems like premature labor and giving birth to a low-birth weight baby. In some cases, the flu infection may also lead to miscarriage and stillbirth.

Other complications (Rare)

The less common complications include:

  • Otitis media or middle ear infection
  • Sinusitis
  • Tonsillitis
  • Febrile seizures
  • Encephalitis
  • Meningitis


The doctors may diagnose influenza just based on the symptoms the patient is feeling.
The diagnosis can be confirmed through some tests such as a sample of fluid taken from the back of the nose or a complete blood count (CBC).

Proper and quick diagnosis is vital to control influenza infection by antiviral treatment.
Also, this may help avoid the inappropriate use of antibiotics, which could result in antibiotic resistance.


Since the flu infection is self-limiting, most people who have it can manage the symptoms at home. In some cases, there is no need to visit a doctor. However, for those who belong to the high-risk groups, it is important to seek medical help for the doctor to prescribe the appropriate antivirals. Only licensed doctors should take medicines since self-medicating could lead to the inappropriate use of medicines and overdose.


Normally, a person with seasonal flu needs nothing more than just bed rest and plenty of fluids. However, some doctors may prescribe antivirals, especially for those who are at a higher risk of complications. The drugs usually prescribed are oseltamivir (Tamiflu) and zanamivir (Relenza).

Managing the symptoms at home

For healthy individuals, the best way to beat the illness is to rest, keep warm and drink plenty of water to prevent dehydration. For those who have a fever, taking paracetamol around-the-clock is advised. However, seek medical help from a licensed doctor before taking ibuprofen. Though it has been previously approved for flu and to relieve aches, it may aggravate the symptoms of other diseases that mimic the signs and symptoms of flu such as dengue fever.


The Centers for Disease Control and Prevention (CDC) says that annual flu vaccinations are important for everyone over the age of 6 months old. Flu vaccines protect from all three or four strains of viruses. Also, these lessen the risk of having complications, which could be deadly for some people.

Control the spread of infection through:

  • Proper and regular hand washing
  • Containing coughs and sneezes by cover the mouth and nose with a tissue.
  • Avoiding crowded places, where flu spreads easily.