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Health Library : Infectious Diseases

 

Influenza

What is influenza?

Influenza (or flu) is a highly contagious viral infection and is one of the most severe illnesses of the winter season. An estimated 5 to 20 percent of the population in the US contract influenza each year.

Influenza is a viral infection of the upper respiratory system, which includes the nose, bronchial tubes, and lungs. Influenza is characterized by the following:

  • Fever
  • Muscle aches
  • Sore throat
  • Nonproductive cough

Influenza can make people of any age ill. Although most people, including children, are ill with influenza for less than a week, some have a much more serious illness and may need to be hospitalized. Influenza may also lead to pneumonia and/or death.

What are the different types of influenza?

Influenza viruses are divided into three types designated as A, B, and C.

  • Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Efforts to control the impact of influenza are focused on types A and B. One of the reasons the flu remains a problem is because the viruses actually alter their structure regularly, exposing adults and children to new types of the virus each time.
  • Influenza type C usually causes either a very mild respiratory illness or no symptoms at all. It does not cause epidemics and does not have the severe public health impact that influenza types A and B do.

Influenza viruses continually mutate or change, which enables the virus to evade the immune system of both children and adults. People are susceptible to influenza infection throughout their lives. The process works as follows:

  1. A person infected with influenza virus develops antibody against that virus.
  2. The virus mutates or changes.
  3. The "older" antibody no longer recognizes the "newer" virus when the next flu season comes around.
  4. Reinfection occurs.

The older antibody can, however, provide partial protection against reinfection. Currently, three different influenza viruses circulate worldwide: two type A viruses and one type B virus. Immunizations given each year to protect against the flu contain the influenza virus strain from each type that is expected to cause the flu within that year.

What causes influenza?

An influenza virus is generally passed from person to person by airborne transmission. This means your child can contract the flu by coming in contact with airborne viruses from an affected person by way of sneezing and coughing. The virus can also live for a short time on objects such as doorknobs, pens/pencils, keyboards, telephone receivers, and eating or drinking utensils, for example. Therefore, it may also be spread when your child touches something that has been handled by someone infected with the virus and then your child touches his/her own mouth, nose, or eyes.

People are generally the most contagious with the flu 24 hours before they start having symptoms and during the time they have the most symptoms. That is why it is hard to prevent the spread of the flu, especially among children, because they do not always know they are sick while they are still spreading the disease. The risk of infecting others usually stops around the seventh day of the infection.

What are the symptoms of influenza?

The following are the most common symptoms of the flu. However, each child may experience symptoms differently.

Influenza is called a respiratory disease, but the whole body seems to suffer when a child has it. Children usually become suddenly ill with any or all of the following symptoms:

  • Fever, which may be as high as 103 degrees F to 105 degrees F
  • Aches and pains
  • Not feeling well "all over"
  • Headache
  • Sore throat
  • Runny or stuffy nose
  • Worsening cough
  • Nausea
  • Vomiting
  • Diarrhea
  • Fatigue

Most people recover from influenza within a week, but may be left feeling exhausted for as long as three to four weeks.

The symptoms of influenza may resemble other conditions or medical problems. Always consult your child's doctor for a diagnosis.

How is a cold different from the flu?

A cold and the flu (influenza) are two different illnesses. A cold is relatively harmless and usually clears up by itself after a period of time, although sometimes it may lead to a secondary infection, such as an ear infection. However, the flu can lead to complications, such as pneumonia and even death. What may seem like a cold, could, in fact, be the flu. Be aware of these differences:

Cold symptoms Flu symptoms
Low or no fever High fever
Sometimes a headache Headache very common
Stuffy, runny nose Clear nose or stuffy nose
Sneezing Sometimes sneezing
Mild, hacking cough Cough, often becoming severe
Slight aches and pains Often severe aches and pains
Mild fatigue Several weeks of fatigue
Sore throat Sometimes a sore throat
Normal energy level or may feel sluggish Extreme exhaustion

How can influenza be prevented?

A new influenza vaccine is introduced each September. All children at least 6 months old should get the flu vaccine this season as soon as it is available in their community. In addition, antiviral medications are approved for use in preventing the flu in children. All of these medications are available by prescription, and a physician should be consulted before any medication is used for preventing the flu.

A nasal-spray flu vaccine, called FluMist, is currently approved to prevent flu due to influenza A and B viruses in healthy children and adolescents (ages two to 17), and healthy adults (ages 18 to 49). As with other live virus vaccines, FluMist should not be given for any reason to pregnant women and people with immune suppression, including those with immune deficiency diseases, such as AIDS or cancer, and people who are being treated with medications that cause immunosuppression. FluMist also should not be given to the following groups of people:

  • Children less than two years of age
  • Any person with asthma
  • Children less than five years of age with recurrent wheezing

Following these precautions may also be helpful:

  • When possible, avoid or limit contact with infected persons.
  • Frequent handwashing may reduce, but not eliminate, the risk of infection.
  • A person who is coughing or sneezing should cover his or her nose and mouth with a tissue or inside elbow to limit the spread of the virus.

Vaccine effectiveness varies from year to year, depending upon the degree of similarity between the influenza virus strains included in the vaccine (those that were predicted to circulate during the flu season) and the strain or strains that actually circulate during the influenza season. Vaccine strains must be chosen nine to ten months before the influenza season. Sometimes, changes occur in the circulating strains of viruses between the time vaccine strains are chosen and the next influenza season. These changes may reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby decreasing the chance that the vaccine will work.

Vaccine effectiveness also varies from one person to another, depending on factors such as age and overall health.

What are the side effects of the vaccine?

The most serious side effect that can occur after influenza vaccination is an allergic reaction in people who have a severe allergy to eggs. For this reason, children who have an allergy to eggs should not receive the influenza vaccine. According to the National Center for Infectious Diseases of the Centers for Disease Control and Prevention (CDC), influenza vaccine causes no side effects in most children who are not allergic to eggs.

Less than one-third of people who receive the vaccine experience some soreness at the vaccination site, and about 5 to 10 percent experience mild side effects, such as a headache or a low-grade fever for about a day after vaccination. Because these mild side effects mimic some influenza symptoms, some people believe influenza vaccine causes them to get influenza. However, according to the CDC, "influenza vaccine produced in the United States has never been capable of causing influenza because the only type of influenza vaccine that has been licensed in the United States to the present time is made from killed influenza viruses, which cannot cause infection."

What are current vaccine recommendations?

While the 2012-2013 flu vaccine will protect you from the same viruses as last year, it is still important to get an annual flu shot because immunity decreases over time. The immunization recommended for all persons age 6 months of age and older, including pregnant women, excluding those who are allergic to eggs or other components of the vaccine. It is especially important that the following groups receive the vaccine:

  • Pregnant women and women who anticipate they may be pregnant during flu season
  • Persons 50 years old or older (Vaccine effectiveness may be lower for elderly persons, but it can significantly reduce their chances of serious illness or death from influenza.)
  • Children six months to 19 years of age
  • Residents of nursing homes and any other chronic care facilities that house persons of any age who have chronic medical conditions
  • Adults and children who have chronic disorders of the pulmonary or cardiovascular systems, including children with asthma, cystic fibrosis, and chronic lung disease of infancy (bronchopulmonary dysplasia, BPD)
  • Adults and children who have the following medical conditions:
    • Chronic metabolic diseases (i.e., diabetes)
    • Renal dysfunction
    • Immunosuppression
    • Hemoglobinopathies
  • Children and teenagers (aged six months to 19 years) receiving long-term aspirin therapy
  • Women who will be pregnant during flu season
  • Health care providers
  • Employees of nursing homes and chronic care facilities who have contact with patients or residents
  • Providers of home care to persons at high risk
  • Household members (including children) of persons in high-risk groups

What is the treatment for influenza?

Specific treatment for influenza will be determined by your child's doctor based on:

  • Your child's age, overall health, and medical history
  • Extent of the condition
  • Your child's tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the condition
  • Your opinion or preference

The goal of treatment for influenza is to help prevent or decrease the severity of symptoms. There is no cure for influenza. Treatment may include:

  • Medications to relieve aches and fever (Aspirin should not be given to children with a fever without first consulting your child's doctor). The drug of choice for children is acetaminophen (Tylenol).
  • Medications used for congestion and nasal discharge
  • Bed rest
  • Increased fluid intake
  • Medication for your child's cough may be prescribed by your child's doctor after a thorough evaluation.
  • Antiviral medications may help to shorten the duration of the illness and to decrease the severity of the flu, but do not cure the flu. They must be started very shortly after symptoms begin. The length of therapy will be determined by your child's doctor.

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