| Influenza is an acute respiratory infection caused by one of three types of influenza viruses in the Orthomyoxoviridae family of viruses. The symptoms, severity, and length of disability attributed to influenza are variable, ranging from fever and fatigue to respiratory failure. Influenza should not be confused with the stomach flu, which is a gastrointestinal condition, not a respiratory condition.
Influenza viruses are designated types A, B, and C. Virus types A and B are constantly changing due to mutations, hence the annual basis need of new influenza vaccines, whereas type C is fairly stable. Type A and type B influenza usually occur during the flu season (November to April), and are more common and more serious forms, associated with higher rates of hospitalization and death. Type C influenza is a milder type of respiratory infection that often does not have any symptoms. The influenza viruses (types A and B) mutate frequently, and so new influenza vaccines are developed annually in anticipation of the expected predominant strain(s). Although immunization against influenza (annual flu shots) can help protect anyone during flu season, it is most important for people at highest risk to receive annual vaccination. Those people allergic to eggs should not receive annual flu shots because the vaccine is cultured in eggs.
Influenza is highly contagious. Spread occurs through airborne respiratory droplets containing the virus. After contact, the affected individual may begin to experience symptoms within 18 to 72 hours; onset can be abrupt (Derlet). Influenza occurs more frequently and severely in smokers or in anyone with compromised respiratory function (e.g., seizure disorders, neuromuscular disorders, or spinal cord injury (“Facts”). The highest morbidity and mortality rates are reported among the elderly and infants, whose immune system functioning is not adequate. Individuals with chronic medical conditions such as asthma, chronic bronchitis, chronic obstructive pulmonary disease (COPD), emphysema, chronic heart disease, diabetes, severe anemia, and kidney dysfunction, are prone to complications of influenza, as are individuals who are immunosuppressed.
Influenza is well known as a cause for epidemics in closed groups, including children in schools and the elderly in long-term care facilities, as well as entire communities or whole countries. Occasionally, there are worldwide pandemics. Epidemics in temperate climates occur during the winter months, but in tropical climates, they can occur at any time.
For information about the A H1N1 influenza pandemic, please refer to the specific topic: Influenza, A H1N1 Virus.Risk: High risk groups include the elderly, infants and pre-school children, and individuals with compromised immune system function (immunosuppression due to medications, HIV, or other immune system disease). Adults with chronic diseases, compromised respiratory function, and pregnant women in the third trimester are at greater risk of complications from influenza (Derlet). Incidence and Prevalence: Influenza epidemics occur in the northern and southern hemispheres virtually exclusively during the winter months but in tropical areas may occur throughout the year. Infections with an influenza virus occur in about 5% to 20% of the US population annually (“Facts”). About 200,000 people are hospitalized annually for complications of influenza (“Facts”). Each year, 20,000 to 36,000 Americans die because of influenza; more than 90% of these deaths are of persons over age 65 (Derlet; “Facts”).
Strains of influenza A viruses and influenza B viruses are found worldwide but prevalence varies in different countries and communities during any flu season. Worldwide pandemics and epidemics have historically resulted in the deaths of 20 to 50 million persons (Derlet). Incidence in various countries varies with the type and strain of the prevalent virus and cannot be accurately predicted. Worldwide incidence can only be estimated in any given influenza epidemic since not all countries record related data. |
Source: Medical Disability Advisor
| History: Common to almost all cases of influenza are fever and systemic symptoms, followed by upper and lower respiratory symptoms several days later. Individuals may report an abrupt onset of fever, chills, headache, muscle aches (myalgia), joint pain, cough, sore throat, runny nose, and fatigue. In some individuals, diarrhea, nausea, and vomiting may be reported. When the systemic symptoms such as chills, fever, myalgia, and fatigue subside somewhat, respiratory symptoms may become dominant as the infection progresses. Physical exam: Upon examination, individuals may seem weary and tired. Their skin may feel warm, and they may have a fever of 101° F to 104° F (38.8° C to 40° C). A runny nose may be evident. The mucous membrane of the throat may appear reddened. Lymph nodes in the neck may be slightly swollen. Accurate diagnosis of influenza is not always possible based on symptom evaluation alone since several other viruses can cause flu-like symptoms, including adenovirus, enterovirus, and paramyxovirus. However, identifying the specific causative virus is not always done since treatment for upper respiratory tract infection (URTI) is fairly standard (Derlet). Tests: Diagnosis of influenza is based primarily on the medical history, symptoms and the physical examination, particularly in the setting of a confirmed influenza outbreak in the community. Viral cultures of material from the nose and throat can be definitive for diagnosing influenza A and B, however they are expensive and require 24 hours minimum for results, so they generally do not influence the type of treatment provided, and are not always performed. Definitive serologic tests and immunofluorescent tests can be performed in the diagnostic laboratory, but they are labor-intensive, time-consuming, and less sensitive than cultures. Rapid tests are also available for diagnosis of influenza. These require a throat or nasal swab sample, and can sometimes be helpful in determining whether a patient should receive antiviral treatment. Although test sensitivity for these rapid methods is 60% to 70%, false negatives for influenza A and B are common (Derlot). For these reasons, during a local outbreak of influenza, the diagnosis is most often made based on symptoms and physical examination alone.
Arterial blood gases may be performed in hospitalized individuals whose breathing is compromised or whose oxygen level is low when monitored. Lumbar puncture may be done to rule out possible meningitis suggested by physical exam findings.
A chest x-ray may be indicated in individuals who are at high-risk of developing pneumonia, including individuals with chronic obstructive pulmonary disease (COPD), the elderly, and the immunosuppressed, or in the individual with abnormalities detected on physical exam. |
Source: Medical Disability Advisor
| Treatment is primarily symptomatic in individuals without complications or underlying chronic illness and includes rest, fluids, pain killers (analgesics), fever-reducing medications (antipyretics), and cough suppressants, if necessary. Antibiotics are not warranted unless a concomitant bacterial infection is suspected. Overexertion during symptomatic illness should be avoided.
Antiviral medications may be used to treat influenza A and B. Although 4 antiviral drugs (adamantanes) against influenza A viruses have been approved for use, the CDC has revised recommendations because of significant resistance to this class of antiviral medication. Neuraminidase inhibitors have been the only recommended medication against both A and B influenza viruses since 2006 (Derlot). Use of these drugs significantly reduces severity and duration of flu symptoms and reduces complications in high-risk groups. To be effective, they must be given within 48 hours of developing symptoms; the greatest effect has been shown if they are given with 6 hours of onset of symptoms (Derlot). Some may be used in the prevention of influenza (prophylaxis), as well. They are available in pill, nasal spray, or inhaler forms. They prevent the spread of influenza by blocking the virus from escaping the already infected cells.
Influenza can be prevented, or its symptoms reduced, by yearly vaccination. The vaccine is effective against both influenza A and B strains. Influenza vaccine is recommended for people who are at high-risk of developing complications due to influenza infection. |
Source: Medical Disability Advisor
| In healthy young and middle-aged adults, full recovery from influenza with no residual effects can be expected in a matter of several days. In older adults and those with underlying pulmonary and cardiac disease, recovery may be prolonged, and the outcome may leave them in a partially disabled condition by worsening their underlying chronic disease process.
The body can be so weakened by influenza that its defenses against bacteria are low. In influenza complicated by bacterial pneumonia, full recovery is expected in healthy young and middle-aged adults. Those who might contract the more serious primary viral influenza pneumonia are at risk of prolonged disability. If they are hospitalized because of respiratory failure, there is a mortality rate of 50%. |
Source: Medical Disability Advisor
| Three types of pneumonia can occur as complications to influenza: viral, bacterial, and mixed viral and bacterial.
Influenza viral pneumonia occurs most frequently in individuals with underlying pulmonary or cardiac disease and in those who are immunosuppressed. It has a rapid, debilitating onset that can require hospitalization. If the pneumonia worsens, it can result in respiratory failure and death. The mortality rate for those with respiratory failure is close to 50%.
Secondary bacterial pneumonia follows a different course. It affects mostly the drug abusers who use needles, hospitalized individuals, and those with chronic medical diseases. Generally, bacterial pneumonia can develop about 5 days after viral influenza. Bacterial pneumonia can be treated with antibiotics.
Mixed viral and bacterial pneumonia generally involves a milder form of viral pneumonia combined with a bacterial pneumonia. The condition will respond at least partially to antibiotic therapy.
Other nonpulmonary complications are rare in adults but can occur. A few of these are toxic shock syndrome, inflammation of the membrane enveloping the brain and spinal cord (meningitis), inflammation in the brain (encephalitis), and inflammation of the heart muscle or lining (carditis or pericarditis). |
Source: Medical Disability Advisor
| Because of the ease with which influenza is transmitted, individuals should stay home until body temperature has returned to normal. Fever may last 2 to 5 days, and individuals should stay home for 2 days after fever is gone. |
Source: Medical Disability Advisor
| If an individual fails to recover within the expected maximum duration period, the reader may wish to consider the following questions to better understand the specifics of an individual's medical case. Regarding diagnosis:
- Did individual have an influenza immunization this year?
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Does individual have respiratory or GI symptoms?
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Is individual a smoker?
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Does individual have asthma, chronic bronchitis, COPD, emphysema, chronic heart disease, diabetes, severe anemia, kidney dysfunction or are immunosuppressed?
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Did individual have an abrupt onset of fever, chills, headache, muscle aches, joint pain, sore throat, runny nose, and fatigue?
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Does individual also report diarrhea, nausea, and vomiting?
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Have respiratory symptoms become dominant?
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On exam, did individual have a fever of 101° F to 104° F (38.8° C to 40° C)?
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Does individual have a runny nose, red throat, or swollen lymph nodes?
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Has individual had a chest x-ray?
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Have conditions with similar symptoms been ruled out?
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Has individual been seen by a specialist?
Regarding treatment:
- Is individual receiving symptomatic treatment such as rest, fluids, analgesics, antipyretics, and cough suppressants, if necessary?
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Did individual seek treatment within 48 hours of the onset of symptoms?
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Is individual being treated with an antiviral medication?
Regarding prognosis:
- Does individual have any conditions that may affect the ability to recover?
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Does individual have any complications, such as viral, bacterial, or mixed viral and bacterial pneumonia resulting in respiratory failure? Does the individual have toxic shock syndrome, meningitis, encephalitis, carditis, or pericarditis?
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Source: Medical Disability Advisor
| "CDC 2009–10 Influenza Season: Questions and Answers." CDC. 9 Sep. 2009. Centers for Disease Control and Prevention. 14 Sep. 2009 <http://www.cdc.gov/flu/about/season/current-season.htm>.Derlet, Robert W., et al. "Influenza." eMedicine. Eds. Klaus-Dieter Lessnau, et al. 11 Jun. 2009. Medscape. 24 Jun. 2009 <http://emedicine.medscape.com/article/219557-overview>. "Facts About Influenza for Adults." National Foundation for Infectious Diseases. 20 May 2005 <http://www.nfid.org/factsheets/influadult.html>. |
Source: Medical Disability Advisor
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