Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at January 11, 2016

Influenza or flu is a contagious respiratory illness that is caused by a flu virus, resulting in mild to severe symptoms. While the flu causes many of the same symptoms as the common cold, the flu has more severe, long-lasting effects and carries a greater potential for causing health complications. Flu is also not to be confused with gastroenteritis or the “stomach flu.”


Definition & Facts

During the colder half of the year, the flu virus spreads, causing seasonal outbreaks of flu. Because flu strains mutate over time, new strains occur every flu season, which is why getting flu vaccines yearly in order to develop immunity to the latest strain is recommended by public health organizations.

Influenza is a cause of serious health complications for those who have a weakened immune system, such as the very young, the elderly, pregnant, and those with heart disease, cancer, asthma and HIV/AIDS. Complications that may develop from flu include viral pneumonia, bacterial pneumonia, bronchitis, sinus infections as well as the worsening of preexisting conditions. People with asthma can suffer severe asthma attacks when they have the virus.

Symptoms & Complaints

Flu symptoms are similar to common cold symptoms except more severe and usually accompanied by fever. While a common cold can increase in severity over a few days, the flu virus hits suddenly and lasts longer.

In addition to fever, people with the flu may suffer hot flashes, cold flashes, and chills. Other symptoms include sore throat, cough, runny nose, body aches, headache and fatigue.

Serious symptoms that need immediate medical attention are shortness of breath, chest pains, sudden dizziness or confusion. Medical attention is particularly important for those with weakened immune system who are suffering these symptoms.


Influenza types A and B are the underlying viruses that cause flu outbreaks. Type A is more common and severe than type B, and is divided into subtypes and strains. While type A is found in animals as well as humans, type B is found primarily in humans. Influenza type C typically does not cause epidemics.

The flu is transmitted similarly to the common cold. It is spread from person to person via direct contact, contact with shared surfaces or objects, and through water droplets. Whenever someone with the flu sneezes or coughs they expel the virus into the air which can be taken in through the eyes, mouth, or nose. The virus can be caught by touching surfaces that others with the infection have touched. Doorknobs, handles, computer parts and phones are common locations for people to contract the virus.

Diagnosis & Tests

Typically doctors will diagnose on the basis of symptoms and whether it's flu season rather than order tests to confirm. This is because knowing definitively if flu or common cold are the cause of symptoms does not usually change the course of treatment.

However, tests can prevent an incorrect diagnosis of a bacterial infection with similar symptoms like bronchitis and thus prevent the unnecessary prescription of antibiotics. They can also enable the doctor to prescribe antiviral drugs. The most common test for flu is the rapid influenza diagnostic test (RIDT) which can return results in thirty minutes.

Treatment & Therapy

The treatment that a patient with the flu needs will depend on the severity of the symptoms as well as his or her health history.

Rest and drinking fluids are commonly recommended for recovery. Over-the-counter medications may be used to remedy symptoms. They include decongestants, anti-histamines, cough suppressants. Acetaminophen and ibuprofen can be helpful in reducing fever and relieving pain.

Antiviral drugs may be prescribed for those who have a high risk medical condition and are showing flu symptoms. However, antiviral drugs are usually only effective within two days of the onset of symptoms. Also, flu viruses develop antiviral resistance making antiviral drugs less effective. Most healthy people who get the flu do not need antiviral drugs.

Prevention & Prophylaxis

Seasonal flu shots or flu vaccines are recommended on a yearly basis for everyone six months and older in order to prevent flu. Children younger than 6 months old or those who have a severe allergy to the flu vaccines or its other ingredients, should not receive the vaccine. It is important that those with high risk medical conditions receive the flu vaccine.

Vaccines cause the body to develop antibodies against the virus contained in the vaccine. Flu shots can be either trivalent, which immunize against three different viruses, or quadrivalent which immunize against four different viruses. Studies estimate that vaccines reduce the risk of flu by 50-60% during flu season.

In order to prevent the spread of flu, those with flu should stay home and avoid close contact with others. Additional good health habits should be practiced such as hand washing, cleaning surfaces, avoid touching eyes, nose or mouth, and covering the mouth and nose when coughing or sneezing.

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