Influenza (Seasonal Flu)

Influenza is a viral infection of the respiratory system caused commonly by the Influenza A, less frequently by Influenza B and rarely Influenza C virus. In temperate countries the illness is seasonal with cases seen primarily in winter and early spring, but in tropical countries it occurs year round.

While most individuals recover uneventfully from this illness it does cause significant morbidity for those less than 2 years of age, greater than 65 years of age or those with chronic medical problems involving the heart, lung, kidney, liver or other immunocompromised conditions. Nearly 90% of deaths due to influenza are seen in those over 65 years of age.

The illness manifests with symptoms of fever, chills, sore throat, runny nose, cough, body aches and muscle pains.

Influenza viruses have been present for hundreds of years and there is a steady rate of infection annually. However, influenza viruses frequently undergo minor genetic mutations called antigenic drift resulting in periodic outbreaks called epidemics where a larger than expected number of people are infected in a community or country. When the viruses undergo major mutations called antigenic shift worldwide outbreaks occur and are called pandemics.

Epidemics occur every 3-4 years while pandemics have so far occurred in the years 1918, 1957, 1968 and 1977.

Where does it occur?

Influenza infections occur world wide. In temperate countries it is seen primarily in winter and epidemics last 6-10 weeks on average. In tropical countries it occurs year round at a lower rate but increases after the rainy season. Map

How is it transmitted?

Influenza is transmitted through exposure to respiratory secretions from infected individuals and through contact with surfaces contaminated with infected respiratory secretions and subsequently touching one’s nose, eyes or mouth.

Is it contagious from person to person?

It is contagious from person to person through respiratory secretions till the individual’s symptoms are resolved.

What is the risk for travelers?

The risk for travelers is moderate to high if traveling to countries where the outbreak is ongoing in large numbers.

How soon after exposure will one develop symptoms?

Symptoms start anywhere from 1-4 days after exposure but usually within 2 days.

What are the signs and symptoms?

Symptoms are sudden onset of high fever, chills, sore throat, runny or stuffy nose, tearing or burning sensation in the eyes, dry cough, body aches and muscle pains. For most people fever, headache and body aches involving the limbs and the long muscles of the back are the most bothersome. Many have flushed appearance to the face, red eye, inflamed throat and hoarseness. Nausea, vomiting and diarrhea are seen in some people, usually children.

Most individual recover in a period of 1-2 weeks but the illness can progress to shortness of breath, respiratory failure and death in a minority of cases.

In some individuals 2-3 weeks after the initial infection has resolved or seems to improve, secondary complications of bacterial pneumonia with cough, high fever, productive phlegm and chest pain; sinusitis with headache, facial pain and fever; otitis media with painful ear, nausea and fever; meningoencephalitis with confusion, stiff neck and seizure; myositis with painful muscles and Reyes syndrome with jaundice, low blood sugars and confusion can occur, especially if they have been on aspirin products.

Are there any lab tests to diagnose the illness?

The virus can be cultured from respiratory secretions. Rapid influenza screening tests are available but have a false negative rate of nearly 30%.

Is there any treatment?

The anti-viral medications tamiflu (oseltamivir) and relenza (zanamavir), amantadine and rimantadine are effective depending on the current strain. Rest, fluids and supportive measures are vital. Cases with respiratory compromise will need ICU support.

What preventive measures can be taken?

Influenza vaccine is preventive and strongly urged for travelers, especially for those at higher risk for complications: those over 65 years of age, have chronic illness involving the heart, lung, kidney or liver.

If there is an ongoing large scale outbreak of Influenza avoid travel to that area, check outbreaks and http://www.cdc.gov/travel.

 If you are already in an area during an outbreak, avoid healthcare facilities and households with ill people.

Wash hands frequently with soap and water or alcohol based cleansers, since viruses can be present on surfaces. Avoid touching your nose and mouth with your hands for no good reason.

Routine wearing of masks and gowns in public area is not recommended by the Centers for Disease Control (CDC).

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