Influenza
Influenza: Excerpt from Professional Guide to Diseases (Eighth Edition)
Influenza (also called the grippe or the flu), an acute, highly contagious infection of the respiratory tract, results from three different types of Myxovirus influenzae. It occurs sporadically or in epidemics (usually during the colder months). Epidemics tend to peak within 2 to 3 weeks after initial cases and subside within a month.
Although influenza affects all age-groups, its incidence is highest in schoolchildren. However, its effects are most severe in persons who are young, elderly, or suffering from chronic disease. In these groups, influenza may even lead to death. The catastrophic pandemic of 1918 was responsible for an estimated 20 million deaths. The most recent pandemics (in 1957, 1968, and 1977) began in mainland China.
Causes and incidence
Transmission of influenza occurs through inhalation of a respiratory droplet from an infected person or by indirect contact with a contaminated object, such as a drinking glass or other items contaminated with respiratory secretions. The influenza virus then invades the epithelium of the respiratory tract, causing inflammation and desquamation.
One of the remarkable features of the influenza virus is its capacity for antigenic variation into numerous distinct strains, allowing it to infect new populations that have little or no immunologic resistance. Antigenic variation is characterized as antigenic drift (minor changes that occur yearly or every few years) and antigenic shift (major changes that lead to pandemics). Influenza viruses are classified into three groups:
❑Type A, the most prevalent, strikes every year, with new serotypes causing epidemics every 3 years.
❑Type B also strikes annually but causes epidemics only every 4 to 6 years.
❑Type C is endemic and causes only sporadic cases.
Each year, tens of millions of people in the United States get the flu; about 114,000 people get sick enough to be hospitalized, and about 36,000 people die.
Signs and symptoms
After an incubation period of 24 to 48 hours, flu symptoms begin to appear: sudden onset of chills, temperature of 101° to 104° F (38.3° to 40° C), headache, malaise, myalgia (particularly in the back and limbs), a nonproductive cough and, occasionally, laryngitis, hoarseness, conjunctivitis, rhinitis, and rhinorrhea. These symptoms usually subside in 3 to 5 days, but cough and weakness may persist. Fever is usually higher in children than in adults. Also, cervical adenopathy and croup are likely to be associated with influenza in children. In some patients (especially elderly patients), lack of energy and easy fatigability may persist for several weeks.
Fever that persists longer than 3 to 5 days signals the onset of complications. The most common complication is pneumonia, which occurs as primary influenza virus pneumonia or secondary to bacterial infection. Influenza may also cause myositis, exacerbation of chronic obstructive pulmonary disease, Reye's syndrome and, rarely, myocarditis, pericarditis, transverse myelitis, and encephalitis.
Diagnosis
At the beginning of an influenza epidemic, early cases are usually mistaken for other respiratory disorders.
CONFIRMING DIAGNOSIS Because signs and symptoms of influenza aren’t pathognomonic, isolation of M. influenzae through nose and throat cultures and increased serum antibody titers help confirm this diagnosis. Also, rapid diagnostic methods for detecting influenza are now available and help confirm this diagnosis.
After these measures confirm an influenza epidemic, diagnosis requires only observation of clinical signs and symptoms. Uncomplicated cases show a decreased white blood cell count with an increase in lymphocytes.
Treatment
Treatment of uncomplicated influenza includes bed rest, adequate fluid intake, aspirin or acetaminophen (in children) to relieve fever and muscle pain, and dextromethorphan or another antitussive to relieve nonproductive coughing. Prophylactic antibiotics aren't recommended because they have no effect on the influenza virus.
Amantadine and rimantadine (antiviral agents) have proven to be effective in reducing the duration of signs and symptoms of influenza A infection.Oseltamivir and zanamivir are effective against influenza A and B infection. In influenza complicated by pneumonia, supportive care (fluid and electrolyte supplements, oxygen, and assisted ventilation) and treatment of bacterial superinfection with appropriate antibiotics are necessary. No specific therapy exists for cardiac, central nervous system, or other complications.
Special considerations
Unless complications occur, influenza doesn’t require hospitalization; patient care focuses on relief of symptoms:
❑Advise the patient to increase his fluid intake. Warm baths or heating pads may relieve myalgia. Give him nonopioid analgesics-antipyretics as ordered.
❑Screen visitors to protect the patient from bacterial infection and the visitors from influenza. Use droplet precautions.
❑Teach the patient proper disposal of tissues and proper hand-hygiene technique to prevent the virus from spreading.
❑Watch for signs and symptoms of developing pneumonia, such as crackles, another temperature rise, or coughing accompanied by purulent or bloody sputum. Assist the patient to gradually resume his normal activities.
❑Educate patients about influenza immunizations. For high-risk patients and health care personnel, suggest annual inoculations at the start of the flu season (late autumn). Remember, however, that such vaccines are made from chicken embryos and must not be given to people who are hypersensitive to eggs. (For people who are hypersensitive to eggs, amantadine is an effective alternative to the vaccine; however it must be started before the flu season and continued throughout the season.) The vaccine administered is based on the previous year's virus and is usually about 75% effective.
❑Inform people receiving the vaccine of possible adverse effects (discomfort at the vaccination site, fever, malaise and, rarely, Guillain-Barré syndrome). Influenza vaccine (inactivated) is recommended for women who are pregnant and who will be in the second or third trimester during influenza season.
❑Live-attenuated influenza vaccine is now available as a nasal spray. Criteria and contraindications for use vary from the inactivated, injectable vaccine. Recipients of live-attenuated influenza vaccine may shed influenza virus for up to 21 days post-immunization.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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