Usually referred to as the flu or grippe, influenza is a highly infectious
respiratory disease. The disease is caused by certain strains of the
influenza virus. When the virus is inhaled, it attacks cells in the upper
respiratory tract, causing typical flu symptoms such as fatigue,
and chills, a hacking
, and body aches. Influenza victims are also susceptible to potentially
life-threatening secondary infections. Although the stomach or intestinal
"flu" is commonly blamed for stomach upsets and
, the influenza virus rarely causes gastrointestinal symptoms. Such
symptoms are most likely due to other organisms such as rotavirus,
The flu is considerably more debilitating than the
. Influenza outbreaks occur suddenly, and infection spreads rapidly. In
the 1918–19 Spanish flu pandemic, the death toll reached a
staggering 20 to 40 million worldwide. Approximately 500,000 of these
fatalities occurred in the United States.
Influenza outbreaks occur on a regular basis. The most serious outbreaks
are pandemics, which affect millions of people worldwide and last for
several months. The 1918–19 influenza outbreak serves as the
primary example of an influenza pandemic. Pandemics also occurred in 1957
and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu
was responsible for 70,000 deaths in the United States, while the Hong
Kong flu killed 34,000.
Epidemics are widespread regional outbreaks that occur every two to three
years and affect 5–10 percent of the population. The Russian flu in
the winter of 1977 is an example of an epidemic. A regional epidemic is
shorter lived than a pandemic, lasting only several weeks. Finally, there
are smaller outbreaks each winter that are confined to specific locales.
The earliest existing descriptions of influenza were written nearly 2,500
years ago by the ancient Greek physician Hippocrates. Historically,
influenza was ascribed to a number of different agents, including
"bad air" and several different bacteria. In fact, its name
comes from the Italian word for "influence," because people
in eighteenth-century Europe thought that the disease was caused by the
influence of bad weather. It was not until 1933 that the causative agent
was identified as a virus.
There are three types of influenza viruses, identified as A, B, and C.
Influenza A can infect a range of animal species, including humans, pigs,
horses, and birds, but only humans are infected by types B and C.
Influenza A is responsible for most flu cases, while infection with types
B and C virus are less common and cause a milder illness.
The annual death toll attributable to influenza and its complications
averages 20,000 in the United States alone. In the United States, 90
percent of all deaths from influenza occur among persons older than 65.
Flu-related deaths have increased substantially in the United States since
the 1970s, largely because of the aging of the American population. In
addition, elderly persons are vulnerable because they are often reluctant
to be vaccinated against flu.
due to complications of influenza are common in children. Among children
with chronic illnesses, about 500 children per every 100,000 between the
ages of birth and age four are hospitalized annually due to influenza,
while about 100 children per 100,000 without chronic illnesses are
hospitalized annually. Among those with underlying high-risk conditions,
infants younger than six months have the highest hospitalization rates
(approximately 10–40 per 100,000 population).
Causes and symptoms
Approximately one to four days after infection with the influenza virus,
the victim is hit with an array of symptoms. "Hit" is an
appropriate term, because symptoms are sudden, harsh, and unmistakable.
Typical influenza symptoms include the abrupt onset of a
, dry cough, and chills, rapidly followed by overall achiness and a fever
that may run as high as 104°F (40°C). As the fever subsides,
nasal congestion and a
become noticeable. Flu victims feel extremely tired and weak and may not
return to their normal energy levels for several days or even a couple of
Influenza complications usually arise from bacterial infections of the
lower respiratory tract. Signs of a
secondary respiratory infection often appear just as the victim seems to
be recovering. These signs include high fever, intense chills, chest pains
associated with breathing, and a productive cough with thick yellowish
green sputum. If these symptoms appear, medical treatment is necessary.
Other secondary infections, such as sinus or ear infections may also
require medical intervention. Children with heart and lung problems, as
well as other chronic diseases, are at higher risk for complications from
With children and teenagers, it is advisable to be alert for symptoms of
, a rare, but serious complication. Symptoms of Reye's syndrome are
nausea and vomiting
, and more seriously, neurological problems such as confusion or delirium.
The syndrome has been associated with the use of aspirin to relieve flu
Although there are specific viral culture tests available to identify the
flu virus strain from respiratory samples, results can take several days.
Therefore, doctors typically rely on a set of symptoms and the presence of
influenza in the community for diagnosis. Specific tests are useful to
determine the type of flu in the community, but they do little for
individual treatment. Doctors may administer tests, such as throat
cultures, to identify secondary infections.
Several rapid (30-minute) diagnostic tests for flu have become
commercially available. These tests appear to be especially useful in
diagnosing flu in children, allowing doctors to make more accurate
treatment decisions in less time.
Essentially, a bout of influenza must be allowed to run its course.
Symptoms can be relieved with bed rest and by keeping well hydrated. A
steam vaporizer may make breathing easier, and
relievers can mask the aches and pain. Food may not seem very appetizing,
but an effort should be made to consume nourishing food. Recovery should
not be pushed. Returning to normal activities too quickly invites a
possible relapse or complications.
Since influenza is a viral infection,
are useless in treating it. However, antibiotics are frequently used to
treat secondary infections.
A transmission electron microscopy (TEM) image of influenza viruses
budding from the surface of an infected cell.
(CNRI/Science Photo Library, National Audubon Society
Collection/Photo Researchers, Inc.)
Over-the-counter medications are used to treat flu symptoms, but it is not
necessary to purchase a medication marketed specifically for flu symptoms.
Any medication that is designed to relieve symptoms, such as pain and
coughing, will provide some relief. Medications containing alcohol,
however, should be avoided because of the dehydrating effects of alcohol.
The best medicine for symptoms is simply an analgesic, such as
or naproxen. (Without a doctor's approval, aspirin is generally
not recommended for people under 18 owing to its association with
Reye's syndrome, a rare aspirin-associated complication seen in
children recovering from the flu. To be on the safe side, children should
receive acetaminophen or ibuprofen to treat their symptoms.)
As of 2004, there were a number of
marketed for treating influenza. To be effective, treatment should begin
no later than two days after symptoms appear. These medications are useful
for decreasing the severity and duration of symptoms. Antivirals may be
useful in treating patients who have weakened immune systems or who are at
risk for developing serious complications. They include amantadine
(Symmetrel, Symadine) and rimantadine (Flumandine), which work against
Type A influenza, and zanamavir (Relenza) and oseltamavir phosphate
(Tamiflu), which work against both Types A and B influenza. Amantadine and
rimantadine can cause side effects such as nervousness,
, lightheadedness, and
. Severe side effects include seizures, delirium, and hallucination, but
are rare and are nearly always limited to people who have kidney problems,
seizure disorders, or psychiatric disorders. Zanamavir and oseltamavir
phosphate can cause
, jitters, and insomnia.
Following proper treatment guidelines, healthy people under the age of 65
usually suffer no long-term consequences associated with flu infection.
The elderly and the chronically ill are at greater risk for secondary
infection and other complications, but they can also enjoy a complete
Most people recover fully from an influenza infection, but it should not
be viewed complacently. Influenza is a serious disease, and approximately
one in 1,000 cases proves fatal.
—A mild illness caused by upper respiratory viruses. Usual
symptoms include nasal congestion, coughing, sneezing, throat
irritation, and a low-grade fever.
—Refers to a situation in which a particular disease rapidly
spreads among many people in the same geographical region in a
relatively short period of time.
—Progressive and usually reversible paralysis or weakness of
multiple muscles usually starting in the lower extremities and often
ascending to the muscles involved in respiration. The syndrome is due to
inflammation and loss of the myelin covering of the nerve fibers, often
associated with an acute infection. Also called acute idiopathic
—A disease that occurs throughout a regional group, the
population of a country, or the world.
A person need not be in one of the at-risk categories listed above,
however, to receive a flu vaccination. Anyone who wants to forego the
discomfort and inconvenience of an influenza attack may receive the
Parents should make sure that their children who fall into any of the risk
categories should be vaccinated against the flu. Pregnant women in the
second or third trimesters should also be vaccinated. Flu vaccines are
available through pediatricians or local public health departments.
Parents should also make sure kids follow good hygiene practices,
including regular hand washing, and covering the mouth when sneezing or
coughing. Children may acquire secondary infections, such as ear
infections or sinus infections, so parents should call the pediatrician if
a child develops a high fever, sudden pain in the ears or sinuses, or
develops a productive cough with thick yellow-green phlegm.
Subbarao, Kanta. "Influenza Viruses." In
Principles and Practice of Pediatric Infectious Diseases
, 2nd ed. Edited by Sarah S. Long et al. St. Louis, MO: Elsevier, 2003.
Wright, Peter. "Influenza Viruses." In
Nelson Textbook of Pediatrics.
Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.
Larkin, M. "Will influenza be the next bioweapon?"
Lancet Infectious Disease
138 (January 7, 2003): 53.
Neff, M. J. "ACIP Releases 2004 Guidelines on the Prevention and
Control of Influenza."
Annals of Internal Medicine
70) (July 2004): 199–204.
Stiver, G. "The treatment of influenza with antiviral
Canadian Medical Association Journal
138 (January 2003): 49–56.
Centers for Disease Control and Prevention.
1600 Clifton Rd., NE, Atlanta, GA 30333. Web site:
National Institute of Allergy and Infectious Diseases (NIAID).
31 Center Drive, MSC 2520, Bethesda, MD 20892–2520. Web site:
, November 2004. Available online at
http://www.niaid.nih.gov/factsheets/flu.htm (accessed December