Influenza - Flu

Influenza, more commonly known as the flu, is a viral illness that affects the respiratory tract.

What is going on in the body?

There are 3 types of influenza viruses: influenza A, B, and C. Each of these has several subtypes. All these forms of the virus mutate (change their genes slightly) and vary from year to year. This is why it is possible for the same person to have repeated episodes of the flu. Flu is usually transmitted from person to person through drops of respiratory discharge.

What are the causes and risks of the infection?

The flu strikes about 7 out of 1,000 people. It is highly contagious. Flu is much more common among people who live in institutional settings such as nursing homes. Those who come in contact with many other people in schools, day care centers, or large group organizations are also more likely to become infected.

The flu season usually begins in late October or early November and goes through the early spring. The number of cases peaks in January and February.

What are the signs and symptoms of the infection?

Symptoms of the flu can include:

How is the infection diagnosed?

A history and physical examination is the first step in diagnosing flu. Most of the time, the healthcare provider can make the diagnosis without further testing. In some cases, lab tests may be ordered, including:

What can be done to prevent the infection?

An injection of flu vaccine every year can provide protection for people who want to avoid the flu. The flu vaccine is produced roughly 9 to 12 months ahead of the flu season. The formula used is based on what experts believe will be the most common strains of flu virus in the coming season. The vaccine has a 60% to 70% success rate in preventing the different types of influenza viruses each year.

The vaccine is recommended for people considered to be at high risk. These include:

A recent study showed that the flu vaccine may also be effective in preventing second heart attacks in people who have already had a heart attack. In the study, people who received the flu vaccine had a 67% lower incidence of a second heart attack than the people who were not vaccinated that year.

Elderly individuals who are vaccinated against the flu have a significantly lower incidence of hospitalization for respiratory disease, congestive heart failure, and death from any cause.

About 25% of adults who receive the flu vaccine report mild soreness at the site of the injection. Young children may develop fever after a flu vaccine. There is also a slight risk of an allergic reaction to the vaccine. A nasal vaccine for the flu is being tested and may soon be available.

What are the long-term effects of the infection?

While most people recover from the flu without problems, others can develop complications such as:

Influenza and its complications can cause serious disease or even death.

What are the risks to others?

The influenza virus is highly contagious. It is transmitted through respiratory secretions. Sneezing and coughing can spread these droplets. The virus can also be passed on when an individual with the flu touches his or her nose and then handles an object that another person later touches. The second person can then pick up the virus from the object and transfer it into his or her own respiratory tract by touching the face.

What are the treatments for the infection?

Flu is generally treated by addressing its symptoms. Bed rest and drinking plenty of fluids help prevent some complications. Antibiotics do not work against the viruses and can reduce the body's ability to fight viruses. Medications such as acetaminophen, ibuprofen, or aspirin can help reduce fever and muscle aches. However, several recent studies showed that people who used fever-fighting medications such as aspirin and acetaminophen had flu symptoms several days longer than those who did not use these medications.

There are currently 4 antiviral medications approved in the US and many other countries to prevent or treat flu. These include:

A decongestant called phenylpropanolamine (PPA), found in many over-the-counter cold remedies, has recently been linked to strokes in young women. The Food and Drug Administation (FDA) has requested that manufacturers stop producing medications containing PPA. In view of the FDA's public health advisory, anyone who has products at home containing phenylpropanolamine should discard them.

What are the side effects of the treatments?

Side effects of fever-fighting medications such as ibuprofen, aspirin, and acetaminophen include stomach upset and allergic reactions. Amantadine can cause anxiety, depression, and insomnia. Zanamivir can cause airway spasm and reduced airflow in people with chronic respiratory disease. Oseltamivir, amantadine, and rimantadine may cause nausea and vomiting.

What happens after treatment for the infection?

Flu symptoms go away in 7 to 10 days for most people. Some people can develop complications, however. The flu can cause pneumonia, even in healthy people.

How is the infection monitored?

A bout of flu usually clears up within 7 to 10 days. Any new or worsening symptoms should be reported to the healthcare provider.

Author:James Broomfield, MD
Date Written:
Editor:Ballenberg, Sally, BS
Edit Date:01/24/01
Reviewer:Eileen McLaughlin, RN, BSN
Date Reviewed:07/13/01