Influenza Diagnosis

  • Diagnosis

    The flu is an infection caused by a virus in the upper breathing passages that may also spread to the lungs. Symptoms include fever, headache, general aches and pains, and extreme exhaustion. The flu is a contagious disease in which the influenza virus is spread through the air by the coughing and sneezing of people who are already infected. The virus is inhaled into the lungs where it attacks tissues involved in breathing. People with the flu usually feel sick rather suddenly, with symptoms that may include fever, headache, and feeling very tired. These symptoms are sometimes followed by coughing and a stuffy or runny nose.

    Once the virus enters your body, it is usually one to four days before you start to feel symptoms. The infection lasts until the body’s immune system can build up a response to the virus and mount a counterattack, usually an additional four to five days.

    Between 35 and 50 million Americans come down with the flu each flu season. Because the types (or strains) of the influenza virus that cause the flu may vary each season, the severity of symptoms and the number of people who become sick also differs. About 10% to 15% of adults in a typical community and a higher percentage of children will come down with the flu.

    Outbreaks of flu occur almost every winter in the northern and southern hemispheres, and can show up year-round in the tropics. Doctors do not know where or how the virus lives between outbreaks. Epidemics usually begin suddenly, peak during a two- to three-week period, and last from two to three months. The first signs of a flu outbreak are usually children with a cough and temperature. Then, adults start to come down with the disease.

    Every 10 to 15 years, people around the world will suffer from the flu. These pandemics, another name for worldwide epidemics, occur when completely new strains of the virus emerge. People become sick because they have not built up immunity to the new type of virus. The pandemic of 1918 killed 500,000 people in the U.S., and more than 20 million people worldwide. Half of the world's population became infected. The last true pandemic took place in 1968-1969. Considered the mildest pandemic of the 20th century, it did not produce an increase in the expected number of flu-related deaths in the U.S. Pandemics can last for several winters until enough people build immunity to the strain.

    The virus that causes the flu spreads through lung and nasal secretions. When someone with the flu coughs or sneezes, some of the virus is expelled into the air, and another person can breathe it in. The flu can also be caught by someone touching an object that another person has sneezed on, and then bringing that hand to his or her face, especially the eyes. Influenza viruses can stay alive in the air for up to three hours. Being in close quarters (in an elevator for example) with someone who has the flu will increase the likelihood of catching the disease. Being in crowded places during the flu season also increases the risk of contagion. Usually someone with the flu stops “shedding” the virus after two to five days from the start of symptoms. Until then, other people can pick up the disease through contact with the patient’s secretions. Hand-to-hand and other personal contact may also spread the virus. Once passed along, the virus grows for one to four days before symptoms develop.

    Three different types of flu viruses cause influenza: influenza A, B, and C. Generally, the worst flu symptoms and 90% of cases of influenza-related pneumonia are caused by influenza A. Influenza B generally produces milder symptoms. However, during an epidemic, even influenza B can cause severe sickness and possibly death. Since these types of flu viruses vary yearly, they are named after the place or animal in which they are thought to have originated—for example, the Asian flu, Hong Kong flu, and swine flu. Influenza C rarely causes human disease, and is more common in swine.

    The flu typically produces a high fever (from 101° to 103°F), a deep and persistent cough, headache, muscle aches, sore throat, weakness or fatigue, and sometimes sneezing and a runny nose. Patients may cough up sputum, which is mucous-like material from the respiratory tract. Blood in the sputum should be reported to the doctor. The cough may last for a week or longer. The fever usually starts to go down after two or three days, but still may last a week. Patients typically complain of muscle aches in the legs and lower back, but soreness could develop in any muscle or in the joints. (It is unknown why the respiratory disease causes symptoms throughout the body.) Patients may also experience a burning sensation in the eyes or an increased sensitivity to the sun.

    Flu symptoms tend to follow a pattern that distinguishes it from a common cold—for example, a cold usually does not cause a high fever Table 01.

    Table 1.  How To Tell A Cold From the Flu

    Symptoms Cold Flu
    Fever Rare Characteristic, high (102?-104?F); lasts 3-4 days
    Headache Rare Prominent
    General aches, pains Slight Usual; often severe
    Fatigue, weakness Quite mild Can last up to 2-3 weeks
    Extreme exhaustion Never Early and prominent
    Stuffy nose Common Sometimes
    Sneezing Usual Sometimes
    Sore throat Common Sometimes
    Chest discomfort, cough Mild to moderate; hacking cough Common; can become severe

    Adapted from "Is It a Cold or the Flu?" from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Department of Health and Human Services.

    Flu symptoms usually come on suddenly. People can often pinpoint the exact time they became ill. However, the disease can also start gradually. Patients become sick from one to four days after being exposed to the influenza virus.

    Difficulty breathing, rapid breaths, and a bluish skin discoloration indicate a serious lung complication. Anyone who has these symptoms should contact a doctor immediately. Nausea, vomiting, and diarrhea may occur with the flu, but are not the main symptoms. Nausea, vomiting, and diarrhea are also symptoms of the somewhat misleading term “stomach flu” (gastroenteritis), which is not caused by the influenza virus. Stomach flu symptoms are caused by other viruses, bacteria, and certain other disorders.

    Being with someone who has the flu increases your risk of coming down with the disease. Because the flu is a contagious disease, contact with people who already have the flu increases your chances of becoming sick. Healthcare workers are at greater risk of acquiring the flu. Outbreaks of influenza B often occur in schools, military installations, and long-term care facilities for older adults.

    Children are two to three times more likely to get the flu than adults. The flu is more common among children and in families with children than in the rest of the population. Children suffering from the flu may have convulsions due to high fevers, and the flu may be followed by ear infections in young children. Children with asthma are at particular risk for developing respiratory complications, including the flu.

    Advanced age and chronic heart and lung conditions place people at increased risk for complications and death, as do some kidney and immune diseases. People with heart and lung diseases requiring ongoing medical care are more likely than others to develop pneumonia and other serious complications of the flu. People with immune diseases such as AIDs or suppressed immune systems, such as people receiving chemotherapy for cancer, are also at increased risk of complications. The majority of flu deaths occur among older people.

    Doctors generally base a flu diagnosis on the patient's complaints, the sudden onset of symptoms, and whether many people in the community have had the disease. While doctors can order tests to determine whether the flu virus is present or whether a person has built up immunity to a flu virus, typical laboratory tests are often not very helpful because they take a couple of days, and the results will most likely not change what action the doctor can take (which is to help ease the severity of the symptoms). The symptoms of the flu differ from the common cold in many ways. Generally with a cold, the patient does not have a fever or headache, and any body aches and fatigue are mild. Patients with the flu generally have a fever, severe headache, muscle aches, and feelings of exhaustion Table 01.

    Doctors will look for signs and symptoms that may indicate a more serious condition. These conditions include such infectious diseases as typhoid fever, meningitis, and tuberculosis. It is important to let your doctor know if you have been exposed to an illness other than flu.

    Diagnostic tests may be ordered if the patient exhibits signs or symptoms of complications, unusual symptoms, or if the patient's immune system does not function normally. If the caregiver suspects that a patient has pneumonia in addition to the flu, he or she may order sputum cultures. Blood tests or a chest x-ray may be needed to help with the diagnosis.

    Annual flu vaccinations have proven very effective in preventing the disease, and produce few adverse reactions. An annual flu shot will help 70% to 90% of young, healthy adults avoid flu symptoms. The vaccine uses strains of inactivated influenza A and B viruses that public health officials expect to be common that year. The amount of protection the vaccine provides depends on how closely the killed virus in the vaccine matches the actual virus infecting people that flu season. (The strains used to make the vaccine are chosen 9 to 10 months before flu season in order to give manufacturers enough time to prepare the vaccine for the public.) It takes the body about one or two weeks after receiving the shot to build up immunity to the flu. The immunity peaks about one to two months later, and then gradually declines. This makes October the ideal time to receive a flu shot in the northern hemisphere.

    A recent study shows that Flumist, the nasal spray, is more effective in preventing children from getting influenza than vaccinations are.

    Those receiving a vaccine may complain of soreness or redness in the arm receiving the injection. New vaccines, which can be inhaled, are under study but not yet available. A small number of people, typically those who have never been exposed to the influenza virus, may feel tired or run a low fever for 8 to 24 hours after receiving the vaccine. The vaccine is produced in eggs, so anyone with a true egg allergy should not be immunized, or should discuss desensitization with their doctor. (Desensitization is a procedure used to help a person’s immune system “get used to” a substance that normally causes an allergic reaction.) Medicare and many other insurance plans cover the cost of a flu shot.

    In addition to preventing the flu, the vaccine may decrease the severity of the disease and the risk of complications. Frail elderly people, who are less able to produce a protective immune response, can still benefit from receiving the vaccine. Studies have shown that influenza immunization can decrease the risk of flu-related hospitalization of elderly patients living in the community by 70%, and the risk of death from complications of the disease by 85%.

    The Centers for Disease Control and Prevention encourages anyone six months of age or older with an existing medical problem and people age 50 and over to receive a flu immunization Table 02.

    Table 2.  Who Should Get a Flu Shot?

    People age 50 and older
    Residents in nursing homes or long-term care facilities
    Patients with heart and lung disorders, including asthma
    Patients who required regular medical care during a preceding year due to?? Diabetes and other long-term diseases?? Kidney problems?? Sickle cell anemia and other such blood disorders?? Suppression of the immune system, due to cancer treatment for example
    Persons who could infect others at high-risk from the flu:?? Physicians, nurses, other healthcare workers, and home care providers?? Members of high-risk patient household

    People at high risk from the flu but who are allergic to the vaccine, or have had an adverse or poor reaction to the vaccine may be given prescription medications as a preventative measure. The antiviral drugs amantadine (for example, Cerebramed and Infectoflu) and rimantadine (Flumadine), which are used to treat an active case of the flu, also can be given as a preventative measure. The drugs can be given once an epidemic has begun, but patients must take it every day during an outbreak.

  • Prevention and Screening

    Annual flu vaccinations have proven very effective in preventing the disease, and produce few adverse reactions. An annual flu shot will help 70% to 90% of young, healthy adults avoid flu symptoms. The vaccine uses strains of inactivated influenza A and B viruses that public health officials expect to be common that year. The amount of protection the vaccine provides depends on how closely the killed virus in the vaccine matches the actual virus infecting people that flu season. (The strains used to make the vaccine are chosen 9 to 10 months before flu season in order to give manufacturers enough time to prepare the vaccine for the public.) It takes the body about one or two weeks after receiving the shot to build up immunity to the flu. The immunity peaks about one to two months later, and then gradually declines. This makes October the ideal time to receive a flu shot in the northern hemisphere.

    A recent study shows that Flumist, the nasal spray, is more effective in preventing children from getting influenza than vaccinations are.

    Those receiving a vaccine may complain of soreness or redness in the arm receiving the injection. New vaccines, which can be inhaled, are under study but not yet available. A small number of people, typically those who have never been exposed to the influenza virus, may feel tired or run a low fever for 8 to 24 hours after receiving the vaccine. The vaccine is produced in eggs, so anyone with a true egg allergy should not be immunized, or should discuss desensitization with their doctor. (Desensitization is a procedure used to help a person’s immune system “get used to” a substance that normally causes an allergic reaction.) Medicare and many other insurance plans cover the cost of a flu shot.

    In addition to preventing the flu, the vaccine may decrease the severity of the disease and the risk of complications. Frail elderly people, who are less able to produce a protective immune response, can still benefit from receiving the vaccine. Studies have shown that influenza immunization can decrease the risk of flu-related hospitalization of elderly patients living in the community by 70%, and the risk of death from complications of the disease by 85%.

    The Centers for Disease Control and Prevention encourages anyone six months of age or older with an existing medical problem and people age 50 and over to receive a flu immunization Table 02.

    Table 2.  Who Should Get a Flu Shot?

    People age 50 and older
    Residents in nursing homes or long-term care facilities
    Patients with heart and lung disorders, including asthma
    Patients who required regular medical care during a preceding year due to?? Diabetes and other long-term diseases?? Kidney problems?? Sickle cell anemia and other such blood disorders?? Suppression of the immune system, due to cancer treatment for example
    Persons who could infect others at high-risk from the flu:?? Physicians, nurses, other healthcare workers, and home care providers?? Members of high-risk patient household

    People at high risk from the flu but who are allergic to the vaccine, or have had an adverse or poor reaction to the vaccine may be given prescription medications as a preventative measure. The antiviral drugs amantadine (for example, Cerebramed and Infectoflu) and rimantadine (Flumadine), which are used to treat an active case of the flu, also can be given as a preventative measure. The drugs can be given once an epidemic has begun, but patients must take it every day during an outbreak.

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