According to The Centers for Disease Control and Prevention (CDC), statistics show that about 5% to 20 % of the U.S. population contracts influenza or flu every year. On average, about 200,000 of these people are hospitalized for flu complications. This is the average annual figure from 1979 to 2001.

However, what the average figure does not tell you is that the number of hospitalized patients shows a rising trend. It does decrease in some years but overall the average trend shows an increase in the number. For example, it ranged from a low of 157,911 in 1990-91 to a high of 430,960 in 1997-98.

Furthermore, about 20,000-50,000 Americans die each year from these complications. According to the World Health Organization (WHO) estimates,  between a quarter to half a million people die from flu complications worldwide. This just shows how deadly this disease can be.

You should be alert and aware of the symptoms of these possible flu dangers and should rush to your doctor at the earliest appearance of any signs.

Flu complications can affect

  • lungs causing pneumonia
  • heart increasing the incidence of heart attacks
  • brain causing encephalitis or meningitis and increasing the incidence of stroke
  • diabetics cause increased blood sugar levels
  • In pregnancy, the flu can cause complications such as premature delivery before 37 weeks and stillbirth.

Flu complications are more common with the type A flu virus, of which H1N1, H1N2, and H3N2 are the only known strains to circulate among humans.

The B virus is not as dangerous or common as the “A” variety. It mutates much more slowly than the “A” variety and has only one serotype.

About 3000 to 49000 people who develop flu complications every year, succumb due to them. 90% of these deaths occur in patients who are above the age of 65 years. These are the averages over 31 seasons between the years 1976 and 2007.

This shows that the majority of the people who get the viral illness, recover without any flu side effects. But, there are those amongst us who are at a higher risk and more prone to developing complications, which can be serious and even fatal.

Flu complications are different from their symptoms. You experience the symptoms when the illness runs a normal course.

Who is more at risk of developing flu complications?

People who are more at risk and prone to developing flu and its complications are:

  • Children below five years of age, but more vulnerable below two years of age
  • The elderly above the age of 65 years
  • Pregnant women
  • Those with chronic diseases of the heart, lung, kidneys, and liver.
  • Diabetics.
  • Those with a compromised immune system.

However, you realize the dangers of this disease by the statistics of deaths caused during the flu epidemics and pandemics. Check them out:

  • The Spanish flu pandemic of 1918 infected 40% of people worldwide and killed 50 million people.
  • The Asian flu of 1957 killed two million people throughout the world.
  • The flu outbreak of 1968, which first started in Hong Kong, killed one million people globally.

A normal flu illness lasts for about a week or two — give or take. The flu symptoms appear suddenly about one to four days after exposure to the flu virus, peak in just two to three days and the severe symptoms can subside as suddenly as they had come two or three days after that. Minor symptoms such as a dry cough and fatigue may linger.

Complications of flu arise when the flu disease gets worse and affects other areas of the body. You don’t see these complications with the normal course of this illness.

Complications of flu often appear just when its main symptoms are subsiding, that is, about five to six days after your fever has subsided. It is like a relapse.

The symptoms and signs of a particular complication indicate the onset of that complication.

The return of the fever indicates the onset of an infective complication. Its symptoms will also start appearing.

Complications that cause worsening of an existing health condition, such as asthma or heart failure will magnify the symptoms and signs of that condition.

Flu complications and their symptoms 

As mentioned above, flu complications usually start to appear when the patient starts to feel better.

Most of the complications are due to superadded bacterial infection, which set in because the viral infection of flu has lowered your immunity.

And, if you happen to be an individual with an already compromised immunity due to age or some preexisting health condition, you become a potential candidate for these complications, which will in the majority of the cases, require hospital admission.  See your doctor promptly, if you experience any symptoms of these complications.

Acute bronchitis

Bronchitis is a common complication of influenza. It is a bacterial infection of the bronchi (airways) in the lungs. There is superadded bacterial infection, which is treated with a course of antibiotics and antiviral agents.

Symptoms of bronchitis include:

  • Fever
  • Cough with sputum, which has turned yellow or greenish due to bacterial infection.
  • Possibly, shortness of breath
  • Headache
  • Sore throat
  • Running or blocked nose producing a yellowish or greenish secretion
  • Body aches
  • Fatigue


Post-influenza, in high-risk persons, a lung infection can develop into pneumonia, which can cause death. This complication of flu is a major cause of morbidity and has a mortality rate of 10-20 percent.

High-risk flu patients such as elderly people over the age of 65 years and children below the age of five years are particularly susceptible because of weak immunity.

Pneumonia of bacterial origin is treated with antibiotics, while these drugs have no effect on viral pneumonia. Viral pneumonia is treated with antiviral agents. Usually, both these types of drugs are needed because you can have both bacterial and viral infections present.

There are cases of healthy individuals becoming acutely ill and dying within hours due to pneumonia and acute respiratory distress syndrome (ARDS).

According to The Centers for Disease Control (CDC), pneumonia combined with the flu ranks as the 8th leading cause of death in the United States every year.

Some common pneumonia symptoms include:

  • High fever of 102˚F or more that is constant and accompanied by chills
  • Cough with expectoration
  • Shortness of breath
  • Pain in chest
  • Headache
  • Bodyache
  • Weakness

With treatment, pneumonia can last for two weeks and longer in people with risk factors. Such people include young children, the elderly above the age of 65 years, people with compromised immunity, and those with health problems such as COPD and asthma.  Healthy people can feel weak for a month after pneumonia has cleared.


Tonsillitis is the infection of your tonsils. Tonsils are two small masses of lymphoid tissue in the throat, one on each side of the root of the tongue.

Flu is primarily an infection of the upper respiratory tract that spreads down into the lungs.

This makes it very easy for the flu virus to latch on to the tonsils and infect them. This will usually invite bacterial infection.

If the infection is caused by the bacterium belonging to the group A streptococcus, it is referred to as strep throat.

The prompt treatment gives you an early cure.

Symptoms include:

  • High fever with chills
  • Cough
  • A sore throat and pain when swallowing
  • This pain can get referred to the ear

On examination, the doctor will find

  • Swollen and enlarged tonsils with spots of pus
  • Swollen lymph glands in the neck


Sinusitis is an inflammation and/or infection of the mucosa (lining) of your nasal cavities (sinuses). Usually, the infection is of viral origin but can get superadded by a bacterial infection.

Symptoms include:

  • Fever
  • Cough
  • Thick and yellow mucus from your nose
  • Headache with pain over the cheeks and the forehead above the eyes. These are the places where the sinuses are located.
  • Blocked nose
  • Congestion
  • A cold that won’t go away or gets worse

Dehydration due to high fever and diarrhea

Any fever can cause dehydration, and so can flu if the patient has not taken the precaution of hydrating herself with fluids and electrolytes. A patient who suffers from dehydration will require hospitalization

Dehydration just does not indicate loss of water from your body, but more seriously the loss of electrolytes such as sodium and potassium.

Dehydration, if not corrected can lead to signs and further complications such as:

  • Muscle cramps due to electrolyte imbalance
  • Seizures again due to the same reason
  • Hypovolemia, which means the decreased volume of blood, due to loss of circulating fluid.  It leads to a drop in blood pressure and in the amount of oxygen circulating in the blood – meaning all your tissues and organs do not get enough blood supply and oxygen. This can be life-threatening.
  • Kidney failure due to hypovolemia

If dehydration is left untreated, it can become severe and cause coma and death.

Otitis media

Otitis media is an infection in the ear behind the eardrum. This part of the ear is called the middle ear. It is more common in infants and children between the ages of 6 months to 3 years and less seen in adults.

Acute otitis media can also be accompanied by fluid buildup inside the ear.

The flu, being an infection of the upper respiratory tract,  easily travels to the ear through the Eustachian tube (a narrow tube leading from the pharynx in the throat to the cavity of the middle ear).

Otitis media can develop within two to seven days after your flu fever has set in.

It is an acute attack initially, which becomes chronic if proper and complete medical treatment is not taken. It can also lead to the perforation of the eardrum.

Symptoms of otitis media in adults include

  • Ear pain
  • Fever
  • Headache
  • Dizziness
  • Tinnitus (ringing in the ears)
  • Ear discharge, which can be purulent or blood-stained
  • Trouble hearing because of plugged ears

Flu complications in people with asthma

In people with existing bronchial asthma, if the flu infection has entered the lungs, it will trigger more asthma attacks with worsening of the asthma condition.

Patients with asthma already have inflamed and sensitive airways. With the flu infection, the condition of the airways gets worse, and patients will get a more severe asthma attack. This can happen even if the patient has controlled his asthma well.

Asthma patients infected with this viral disease tend to develop pneumonia.

Flu complications in patients with COPD

Patients with COPD are at a very high risk of developing lung-related flu complications such as pneumonia. Both flu and COPD are high-risk factors for respiratory failure. In patients with both these conditions, there is a higher risk of life-threatening exacerbations and respiratory failure.

Flu complications can cause severe difficulty in breathing in patients with asthma and COPD

Flu complications in patients with heart disease and stroke

According to the CDC, flu patients who have existing heart failure or stroke are at a much higher risk of developing heart attacks, myocarditis, and stroke. Heart conditions include heart failure, heart attack, acute coronary syndrome, and angina.

If you have any existing chronic condition such as heart failure, diabetes, or bronchial asthma, the flu can worsen these conditions and trigger their symptoms. People with these health problems must take special care to take the flu shot every year.

According to the CDC, “41% of adults hospitalized with the flu during the 2015-2016 flu season had heart disease. Studies indicate that influenza is associated with an increased rate of heart attacks and stroke”.

Influenza complications in patients with diabetes.

Diabetes, both type 1 and type 2, even if well controlled, weakens the immune system. Diabetics, therefore, are very prone to catch the various flu complications mentioned here.

Vice versa, flu worsens diabetes because infections raise blood sugar levels and make it difficult to control it.

According to, The CDC encourages people with diabetes to prompt medical treatment as soon as flu is diagnosed and treatment with anti-virals is initiated. These medications work more effectively if started in the first 48 hours of having the flu, and they give results faster.

Flu complications of the brain 

Encephalitis is an inflammation of the brain tissue and meningitis is inflammation of the meninges, which are the membranes that cover the brain and spinal cord.

Both these complications can be caused by the flu virus. They are rare but when they occur, they can cause serious repercussions.

These infections usually are due to the virus, but bacterial infection has to be ruled out as it can be more serious. 10% of people with bacterial infection die and one out three are left with long-lasting effects such as brain damage, loss of sight, and hearing.

Symptoms of encephalitis and meningitis onset suddenly and include

  • High fever  (103°F or higher)
  • Vomiting
  • Persistent headache
  • Confusion and impaired judgment
  • Weakness
  • Lethargy
  • Photophobia (increased sensitivity to light)
  • Seizures
  • Stiff neck

Both these brain complications respond to treatment and most people recover. But, the high-risk groups are especially prone to dangerous consequences such as brain damage and more seriously, death.

Flu complications in pregnancy

Pregnant women are at a higher risk of developing complications because of lowered immunity during this period.

Flu can cause you to go into premature labor before 37 weeks. However, if you deliver, flu can cause your baby to have a low weight.

More seriously, it can cause a miscarriage or your baby can be born dead (stillbirth).

Sepsis due to influenza   

Sepsis also called blood poisoning, is the infection of the blood. The medical fraternity admits that the incidence of sepsis goes up during the flu season.

The prognosis is bad. Worldwide, one-third of the people who develop sepsis succumb to it. Those who survive experience some long-lasting effects. These include post-traumatic stress disorder (PTSD), chronic pain and fatigue, and organ dysfunction.

Sepsis progresses through three stages, namely sepsis, severe sepsis and septic shock. Symptoms of each stage show progressive severity and all symptoms need not be present.

Symptoms of sepsis include:

  • Body temperature above 101F or below 96F
  • Increase in heart rate above 90 per minute
  • Increased rate of breathing above 20 per minute

Symptoms of severe sepsis include:

  • Significantly decreased urine output
  • Abrupt mental changes leading to confusion, lethargy, delirium, dementia
  • Encephalopathy
  • Decreased platelet count
  • Difficulty in breathing
  • Cardiac dysfunction
  • Abdominal pain

Symptoms of septic shock

Septic shock is characterized by symptoms of severe shock and a sudden and severe drop in blood pressure.

Rare flu complications

Not all the complications mentioned above are common. Some of them are less common and include:

  • Tonsillitis
  • Otitis media
  • Febrile convulsions (seizures)
  • Encephalitis
  • Meningitis