Influenza | Description | Prevention | Causes and symptoms | Treatment
Definition
Influenza, also referred to as the flu, is a highly contagious disease of the nose, throat, and lungs that is caused by an influenza virus.
Description
There are three types of influenza viruses , A, B, and C. Influenza Types A and B viruses cause seasonal epidemics of disease most winters in the United States. Influenza Type C viruses cause only mild respiratory illnesses, are not thought to be responsible for epidemics, and are not included in influenza vaccines. There are two types of subtypes of Influenza A viruses found in human beings: H1N1 and H3N2. Influenza B viruses do not exhibit subtypes. Type A viruses tend to affect adults while Type B viruses affect children. Each year strains of Influenza A subtype H1N1 and H3N2 and a strain of Influenza B are included in the influenza vaccine. The strain of viruses included in the vaccine change yearly based on international surveillance data of influenza cases and estimations by scientists on what types and strains of viruses will be prevalent in the coming year. When the strains included in the vaccine are well-matched to the strains in the community, the vaccine usually can protect seven to nine out of ten vaccinated persons. However, in elderly people, the vaccine may not work as well to prevent contracting of influenza, but will result in decrease in the severity of symptoms and the risk of health complications.
The illness known as stomach flu is not a form of influenza. The influenza virus normally does not attack the stomach or intestines. Stomach flu is caused by other organisms, such as salmonella orEscherichia coli bacteria.
Influenza season can run from as early as October and can last as long as May. Winter is usually the prime season for influenza, as flu activity has peaked in January during 26 of the last 30influenza seasons. During a single influenza season, there may be more than one outbreak of activity due to infections by different strains of the influenza viruses, and an individual may getinfluenza more than once.
Periodically an influenza strain arises that is very different from other strains. When this major change occurs, a world wide epidemic, called a pandemic, can develop. Few people will have antibodies against the new virus. In 1918-1919, such a pandemic occurred due to an influenza outbreak referred to as the Spanish flu, and it is estimated that 40 to 100 million people died. In 1957-58 the Asian flu pandemic killed 1 to 1.5 million people, and the Hong Kong flu pandemic in 1968-1969 killed 0.75 to 1 million people.
Demographics
About 10 to 20 percent of the United States population contracts influenza each year. An average of 36,000 people die from influenza-related complications and more than 200,000 are hospitalized. More than half of those hospitalized are people aged 65 years or older, as senior citizens are generally more at risk for serious influenza complications.
Causes and symptoms
In healthy adults, influenza is typically a moderately severe illness. However in adults over the age of 65 and for people with health problems, influenza may be a dangerous disease. Influenza usually starts abruptly, with a high fever of 102 to 106 degrees Fahrenheit. The fever lasts for a day or two, but may last up to 5 days. Other symptoms include flushed face, body aches and chills, nausea, loss of appetite, weakness, and lack of energy. Some people may have dizziness or vomiting. After two to four days, respiratory symptoms, such as a dry, hacking cough, nasal discharge, and sneezing, appear and last for four to seven days. The patient may also suffer from sore throat and headache and the fever could return. Coughing and fatigue can last for weeks after the acute symptoms subside. It is recommended that a person stay at home as long as the illness is severe, and for about two days after the fever subsides. Generally the symptoms of influenza are more severe than those of the common cold . Cold symptoms rarely include fever, headache, aches and pains, and extreme exhaustion.
The most common way to become infected with an influenza virus is by breathing in droplets from the coughs or sneezes of an infected person. The disease can also be contracted by persons touching a contaminated surface and then touching their mouth, nose, or eyes. After a person is infected with an influenza virus, symptoms usually appear within 2 to 4 days, and the person is contagious for another 3 to 4 days after the symptoms appear.
Adults over the age of 65 who contract influenza are more likely to develop serious complications, thus affecting their health and their independence . Diseases that place persons at high risk include:
· chronic lung diseases such as asthma, emphysema, chronic bronchitis, tuberculosis, or cystic fibrosis
· heart disease
· chronic kidney disease
· diabetes or other chronic metabolic disorders
· severe anemia
· diseases or treatments that depress the immune system
QUESTIONS TO ASK YOUR DOCTOR
· What can I do to relieve my symptoms?
· Do I need further testing to see if I have developed influenza-related complications?
Possible complications that may develop, especially for those at high risk, include pneumonia , encephalitis, bronchitis , sinus infections, ear infections, or exacerbation of existing chronic diseases such as congestive heart failure , asthma , or diabetes. Most people who die from influenza-related complications are 65 years or older.
Diagnosis
To diagnosis if a person has influenza, a thorough physical examination should be conducted. When influenza is widespread in a community, such an examination of symptoms may be sufficient for diagnosis. However, based on symptoms alone, it may be difficult to distinguish influenza from such diseases caused by infectious agents such as Mycoplasma pneumoniae, adenovirus, respiratory syncytial virus, rhinovirus, parainfluenza viruses, and Legionella species. An antigen detection test of a sample collected from the nasal passages (nasal swab) should conducted to provide a definite diagnosis if results are needed to determine appropriate treatment decisions. A chest x-ray should be performed if pneumonia is suspected, as pneumonia is a common complication of influenza. If there is an outbreak of illness in a hospital or a nursing home, testing for influenzamay be required to determine the cause of the outbreak. Collection and analysis of selected samples will also provide information on what strains are causing illnesses, compared to the strains included in the annual vaccine, as well as provide information on new strains to be considered for the next year's vaccine.
Treatment
Rest, the use of symptom-relieving medications, and ingestion of liquids are sufficient treatments for persons with low risk of complications and mild symptoms. The use of aspirin , alcohol, and tobacco should be avoided, and antibiotics are not necessary, unless bacterial complications arise. If symptoms do not improve after several days, or if symptoms get progressively worse, a person should visit a physician to be checked for possible complications.
If the flu is diagnosed within 48 hours of when symptoms begin, antiviral medications may be taken to help shorten the duration of the illness and reduce the severity of the symptoms. The medications are not effective if taken more than 48 hours after onset of the disease. The use of antiviral medication may also prevent the development of influenza-related complications.
Two antiviral medications that are available are oseltamivir and zanamivir. The recommended duration of treatment with these medications is five days. Potential side effects of oseltamivir are vomiting or nausea, while rare cases of self-injury or delirium have been reported. Zanamivir should not be used by persons with respiratory diseases such as asthma or chronic obstructive pulmonary disease . Oseltamivir can be taken in capsule or oral suspension form, while zanamivir is self-administered by oral inhalation.
Two other licensed influenza antiviral agents are available in the United States: amantadine and rimantadine. Since Influenza A virus resistance to amantadine and rimantadine can emerge rapidly during use, the Advisory Committee on Immunization Practices of the Center for Disease Control recommended that neither amantadine nor rimantadine be used for the treatment or prevention ofinfluenza A in the United States during the 2007-08 influenza season.
Nutrition/Dietetic concerns
By maintaining a healthy diet , a person is more likely to have a stronger immune system , which in turn reduces the risk of getting influenza and perhaps lessening the duration and severity of symptoms if influenza is contracted.
Prognosis
Tens of millions of people in the United States get influenza each year. Most people who get influenza recover within a week or two but thousands do become hospitalized. About 36,000 people die yearly in the United States because of influenza-related complications.
Prevention
The best way to prevent contracting influenza is to get an annual influenza vaccination . The vaccination, which is safe and effective, takes about two weeks to provide protection againstinfluenza. In the United States the Medicare program covers the cost of the vaccine.
KEY TERMS
Epidemic —The occurrence of more cases of a disease than would be expected in a community or region during a given time period; a sudden severe outbreak of a disease.
Pandemic —An epidemic (a sudden outbreak) that becomes very widespread and affects a whole region, a continent, or the world.
Vaccination —Injection of a killed or weakened microbe in order to stimulate the immune system against the microbe, thereby preventing disease. Vaccinations, or immunizations, work by stimulating the immune system, the natural disease-fighting system of the body. The healthy immune system is able to recognize invading bacteria and viruses and produce substances (antibodies) to destroy or disable them. Vaccinations prepare the immune system to ward off a disease. To immunize against viral diseases, the virus used in the vaccine has been weakened or killed.
Virus —A microorganism smaller than a bacteria, which cannot grow or reproduce apart from a living cell. A virus invades living cells and uses their chemical machinery to keep itself alive and to replicate itself. It may reproduce with fidelity or with errors (mutations)-this ability to mutate is responsible for the ability of some viruses to change slightly in each infected person, making treatment more difficult.
Antiviral drugs oseltamivir and zanamivir, which can be taken by persons who have not yet contracted influenza, are 70 to 90 percent effective in preventing influenza and are useful to use in conjunction with vaccination. An antiviral drug must be taken every day during potential exposure toinfluenza or for 14 days after receiving an influenza vaccination, to allow time for immunity to develop.
As influenza is easily passed through sneezing, coughing, and contact with contaminated surfaces, staying away from people with the flu and frequent hand washing with soap and water or with an alcohol-based hand cleaner are also methods of preventing influenza infections.
Caregiver concerns
Caregivers of the elderly should receive influenza vaccinations annually to protect the people in the care from getting the disease. Vaccination of health care professionals has been associated with fewer deaths among nursing home patients and elderly hospitalized patients. However, only 42 percent of health care professionals become vaccinated in the United States each year. Duringinfluenza outbreaks, even caregivers who have been vaccinated should consider taking antiviral drugs, especially when caring for seniors at high risk for complications.
Resources
BOOKS
Monto, Arnold S. Contemporary Diagnosis, Prevention, and Management of Influenza. Newtown, PA: Handbooks in Health Care Company, 2002
Schachter, Neil. The Good Doctor's Guide to Colds and Flu.
New York, NY: HarperCollins Publishers, 2005.
Williams, J.E. Beating the Flu: The Natural Prescription for Surviving Pandemic Influenza and Bird Flu. Charlottesville, VA: Hampton Roads Publishing Company, 2006.
ORGANIZATIONS
Centers for Disease Control and Prevention Influenza, www.cdc.gov/flu/.
National Institute of Allergy and Infectious Diseases, National Institutes of Health,http://www3.niaid.nih.gov/healthscience/healthtopics/Flu/default.htm.
Judith L. Sims
