Flu Information in this issue provided by the Public Health Service of the U.S. Dept of Health and Human Services

Flu Facts

Influenza, or flu, is an acute respiratory infection caused by a variety of influenza viruses. The first flu virus was identified in the 1930's. Since then, scientists have classified flu viruses into types A, B, and C.

Type A is the most prevalent and is associated with the most serious epidemics. Type B outbreaks also can reach epidemic levels, but the disease it produces generally is milder than that caused by type A. Type C viruses, on the other hand, never have been connected with a large epidemic.

Outbreaks of flu usually begin abruptly. As the disease spreads through communities, the number of cases peaks in about 3 weeks and subsides after another 3 or 4 weeks. Twenty to fifty percent of a population may be affected.

Besides the rapid onset of the outbreaks and the large numbers of people affected, flu is important because of the seriousness of the complications that can develop. Most people who contract the disease recover within a week (although they may tire easily for awhile). However, for elderly people, newborn babies, and people with certain chronic illnesses, flu and its complications can be life-threatening.

Viruses that cause flu spread primarily from person to person, especially by coughing and sneezing (via airborne droplets of respiratory fluids). Flu viruses can enter the body through the mucous membranes of the eyes, nose, or mouth.

After a person has been infected with the virus, infection is considered contagious for another 3 to 4 days after symptoms appear.

The greatest risk of infection is in highly populated areas. Isolating people with flu symptoms is not an effective means of disease control because flu can be spread by someone whose symptoms are not yet apparent.

Flu is usually signaled by headache, chills, and dry cough, which are followed rapidly by body aches and fever. Typically, the fever starts declining on the second or third day of the illness. It is then that the upper respiratory symptoms become noticeable-nasal congestion and sore throat. Flu almost never causes gastrointestinal symptoms; the illness that people call "stomach flu" is not influenza.

Each strain of virus has different surface antigens, and the immune system produces antibodies specific to each antigen. The antigens of an attacking virus also leave an imprint on the memory of the immune cells so that they can respond immediately to a second exposure of the same antigens and prevent a second infection.

Unlike antigens of other viruses, the surface antigens of flu viruses change periodically. Persons with antibodies stimulated either by previous infection or vaccination are not protected from infection with new strains of flu virus.

Each year, scientists formulate a new vaccine made from inactivated (killed) influenza viruses. The preparation is based on the strains in circulation at the time, yet includes those A and B viruses expected to circulate the following winter. Sometimes, an unpredicted new strain may appear after the vaccine has been manufactured and distributed, resulting in infection even among those who received flu vaccine. Usually, however, the disease is milder because the vaccine will provide some protection.

Since the immune system takes time to respond to vaccination, the inactivated vaccine should be given 6 to 8 weeks before flu season begins in order to stimulate enough antibodies to prevent infection or reduce the severity of the illness. The vaccine itself cannot cause flu, but someone could become exposed and infected soon after vaccination, before antibodies develop.

The most common side effect of the vaccine is soreness at the site of the vaccination. Others include fever, tiredness and sore muscles that may begin 6 to 12 hours after vaccination and may last for up to 2 days.

Flu complications (which can either accompany or follow the illness) generally result from bacterial infections in the lower respiratory tract. The ensuing pneumonia usually is caused by pneumococcal bacteria.

Symptoms of complications usually appear after the flu patient starts feeling better. This brief period of improvement is followed by the sudden onset of high fever, shaking chills, chest pain with each breath, and coughing that produces thick, yellow-greenish-colored sputum. Although most people with pneumonia recover after treatment with antibiotics, some pneumonia-causing organisms are resistant to these drugs.

Once a person has the flu, treatment usually consists of resting in bed, drinking plenty of fluids, and taking medication such as aspirin or acetaminophen to relieve fever and discomfort.

Antibiotics are not effective against flu viruses.

The drug rimantadine can be used to treat influenza type A virus infections in adults. It has no effect on influenza type B infections. When taken within 48 hours after the onset of illness, it reduces the duration of fever and other symptoms and allows flu sufferers to return to their daily routines more quickly.

Rimantadine is a derivative of the drug amantadine, which also can prevent and treat flu infection. Amantadine, however, is more likely to cause side effects such as lightheaded-ness and inability to sleep more often than is rimantadine.

Rimantadine and amantadine may also be used by family members or close contacts of influenza A patients who have been vaccinated but may need added protection.

Pandemics are the result of antigenic shifts and are associated with severe illness and significant mortality on a global scale. Within this century, at least five pandemics and numerous epidemics (regional outbreaks involving fewer people) have occurred. The 1968 Hong Kong outbreak was severe because the antibodies people had developed to protect them against the Asian strain were ineffective against the new strain.

The Russian flu pandemic in the winter of 1977-8 was caused by a strain of virus identical to the one that caused an epidemic in 1950. This virus had somehow been preserved in its original form for 27 years. The Russian pandemic primarily affected people under 25 years of age, indicating that people who had been exposed to the virus in 1950 had developed and maintained immunity. This phenomenon led scientists to recognize that the natural immunity resulting from influenza infection can last more than two decades.

The flu typically kills about 20,000 people a year. When a Type A virus is widespread, as many as 40,000 people can die.
The CDC does not have a final number of deaths from the 1996-97 season. But the flu was widespread in 38 states by December, and deaths soared above expectations during a 10-week stretch from December to February.

Flu is becoming dangerous if fever persists, if fever rises after going down, or if a dry cough turns wet, you may have developed pneumonia or some other complication of flu. You should see your doctor if you have any doubt about your recovery from the flu. You also can get a shot to prevent pneumococcal pneumonia - the type of pneumonia most older people get. The shot has few side effects, cover 23 strains of pneumonia and you only need to get it once.

It is easy to confuse a common cold with the flu. A cold usually doesn't cause a fever - the flu does. A cold causes a stuffy nose more often than flu does. Overall, cold symptoms are milder and don't last as long as the flu.

People used to think the flu was caused by the “influence of the stars and planets.” In the 1500's, the Italians called the disease “influenza,” their word for influence.