What You Should Know About Flu

What is flu?

What You Should Know About Flu

Flu is a short form of 'Influenza', a quickly spreading respiratory disease; it is caused by a virus, and has symptoms of fever, inflammation of the respiratory tract, extreme exhaustion and muscle pain. Its seasonal outbreak afflicts several states of India, year after year.

In medical terminology, the disease is called Acute Febrile Respiratory Illness (AFRI) or Influenza Like Illness (ILI).

Common cold and flu

Often it is difficult for you to differentiate between flu and common cold; certain symptoms like body pains, weakness, runny nose, sneezing, sore throat and chest discomfort are common for both.

But it is flu, not cold, that is characterized by a 3-to-4-day fever of 100 - 102° F, prominent headache, extreme exhaustion and complications of bronchitis and pneumonia.

Types of flu virus

There are three types of influenza viruses A, B and C, and they keep changing their structure over time. They pose a challenge to health care providers worldwide, as new vaccines need to be made available to treat effectively the newer strains of these viruses.

The total number of laboratory confirmed cases as of March 2015 in India alone crossed the 33000 mark, with a death toll of more than 2000 people. Currently, over 98% of the seasonal influenza A strain cases confirmed is of the type H1N1, also called swine flu, which can spread quickly across the world.

Type B influenza virus too causes the annual flu epidemics. Also, type C can cause flu; however, its symptoms are much milder. It does not generally make you very ill, nor does it trigger epidemics.


In temperate climates, flu records its highest prevalence in winter. However, in a tropical country like ours, flu occurs all year round with most cases reported in the rainy months.

The attack rate and the frequency of isolation of flu are highest in young children. Moreover, children infected with influenza viruses are carriers of higher levels of the viruses, which they can transmit effectively over a prolonged period.


What You Should Know About Flu

When a person affected by flu coughs, sneezes or talks, numerous tiny droplets carrying the viruses are released into the air, which can infect people six feet away.

Also, you can be infected by the flu viruses, if you happen to touch objects like bed linen, cups or plates infected by the viruses, and then touch your nose, mouth or eyes. You can, in turn, pass on the infection to others, even before you start showing symptoms of flu. That is why isolation of the sick becomes difficult.

Thus you are not only a carrier, but also a transmitter of the disease from day one up to a week after you fall sick.

Clinical features

Fever is the most commonly observed symptom present in more than 90% of the cases; others include a dry, non-productive cough (80%), nasal blockage or persistent watery mucus discharge from the nose (80%), headache, sore throat, muscle or body aches, fatigue and extreme exhaustion.

In previously healthy individuals, symptoms typically subside without treatment in 5 to 8 days.


Respiratory Complications

Pneumonia is the commonest respiratory complication of the flu. It is a primary bacterial infection of the lungs that triggers symptoms of cough, fever, shaking, chills, and other side effects.

Acute respiratory distress syndrome (ARDS) is another complication that reduces the supply of oxygen to the lungs and the blood, and can become very dangerous. Secondary bacterial pneumonia may seriously complicate flu in children and adults.

Non-respiratory complications

Nonrespiratory complications of influenza are relatively infrequent, but can be extremely dangerous; they include damage to the brain, inflammation of the lining around the heart, destruction or degeneration of muscle tissue and kidney failure.

Central nervous system complications that are more common in children than adults are: acute infection and inflammation of the brain; inflammation of the spinal cord or of the bone marrow; attack of the immune system on nerves, leading to muscle weakness and even paralysis.

Perhaps, the most severe post-infectious complication of influenza is a swelling of the liver and the brain, associated with a variety of viral infections.

People at high risk for developing flu complications

The following are at high risk for developing flu complications:

1. Children younger than 5 years of age (especially kids less than 2 years)

2. Adults 65 years and older

3. Pregnant women

4. Residents (of any age) of nursing homes

5. Patients with weak immune system (because of HIV, cancer, transplant, or use of steroids)

6. People with the following medical conditions:

• Asthma, chronic pulmonary disease e.g. cystic fibrosis (severe damage to the lungs and digestive system caused by the production of unusually thick and sticky mucus)

• Hemodynamically significant cardiac disease

• Neuromuscular disorders, seizures, cognitive dysfunction.

• Chronic metabolic diseases e.g. diabetes mellitus

• Chronic kidney disease

• Diseases of the blood and bone marrow e.g. hemogobinopathies, sickle cell disease


The clinical diagnosis of flu is difficult to make irrespective of age groups, and is likely to go wrong: especially children and the elderly may not initially have typical symptoms of flu.

• The World Health Organization states that Influenza infection is not easily distinguished from other respiratory infections.

• Therefore, WHO defines 'Influenza Like Illness' (ILI) as an acute respiratory infection with measured fever of 38° C (100.4° F) or more, and cough that begin within the last ten days.

• It is stated further that the definition is not intended to capture all cases, but to describe trends over time.

In the absence of another diagnosis, the definition was demonstrated to have, across countries, a sensitivity of 50% and specificity of 87% in differentiating influenza from noninfluenza illnesses. The syndrome of acute onset of fever and cough has been identified as the strongest predictor of influenza.

Lab testing (with samples of nasal oozing, nasopharyngeal aspirate, throat swab, sputum, endotracheal aspirates and washes, and bronchoalveolar lavage) can help avoid unnecessary further tests and administration of antibiotics; more importantly, it can help initiate timely action to prevent disease outbreaks.

Management Principles

The three important principles of management of flu are supportive care, treatment with antiviral drugs and control of infection outbreak.

Treatment with antiviral drugs

All cases of 'highly suspected' or 'lab-confirmed' influenza should be treated promptly with antiviral drugs, regardless of the vaccination status or the severity of illness. In children, the drugs oseltamavir (capsule or liquid) and zanamavir (inhaler medicine) shorten the duration of illness by a day and a half, if started within 48 hours of illness onset.

Prevention of infection with antiviral drugs

The following persons should be treated promptly with oseltamivir or zanamavir for prevention of infection.

• Persons in contact with those at 'high risk'

• All vaccinated and unvaccinated residents of institutions such as nursing homes and facilities exposed to influenza outbreaks

The following table can be used as a guideline for treatment or prevention of flu with the antiviral drug oseltamavir or zanamavir.

What You Should Know About Flu


Vaccination is vital for prevention of influenza and its complications. A yearly flu vaccine is recommended for every one of age 6 months and older.

Trivalent inactivated vaccine (TIV) recommendations

Trivalent flu vaccine protects against two influenza A viruses (an H1N1 and an H3N2) and an influenza B virus. It should be administered annually before the flu viruses become active in your community. It should be continued as long as the viruses continue to spread.

• TIV is recommended for all children of age 6 months and more.

• TIV can be administered to healthy children aged 2 years and more.

• Children aged 6 months through 8 years need 2 doses of the vaccine 4 weeks apart.

• TIV should be administered to all children and adolescents associated with increased risk for complications of influenza.

• TIV or Live Attenuated Influenza Vaccine (LAIV) should be administered to the following groups to prevent transmission of influenza to those at risk:

 -  Contacts of children more than 5 years

 -  Contacts of patients with weak immune system

 -  Pregnant women

 -  Health care professionals

Article by Dr. Lakshmi Prashanth, MD (AIIMS)
Consultant Pediatrician, Kauvery Hospital, Chennai


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