Influenza - Causes, Symptoms and Treatment

Definition:

Also called the grippe or the flu, influenza is an acute, highly contagious infection of the respiratory tract that results from three types of Myxovirus infiuenzae. 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 1 month.

Although influenza affects all age­groups, its incidence is highest in schoolchildren. Its severity is greatest in the very young, elderly people, and those with chronic diseases. In these groups, infiuenza 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 of Influenza

Transmission of infiuenza occurs through inhalation of a respiratory droplet from an infected person or by indirect contact, such as the use of a contaminated dlinking glass. The infiuenza 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. Such variation leads to infection by strains of the virus to which little or no immunologic resistance is present in the population at risk. 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). Infiuenza 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 only causes epidemics every 4 to 6 years.
• Type C is endemic and causes only sporadic cases.

Signs and Symptoms of Influenza

After an incubation period of 24 to 48 hours, fiu symptoms begin to appear: the sudden onset of chills, a 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 ones), 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 can be primary influenza viral 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 for Influenza

At the beginning of an infiuenza epidemic, early cases are usually mistaken for other respiratory disorders. Because signs and symptoms are not pathognomonic, isolation of M. infiuenzae through the inoculation of chicken embryos (with nasal secretions from infected patients) is essential at the first sign of an epidemic. In addition, nose and throat cultures and increased serum antibody titers 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 for Influenza

Uncomplicated influenza is treated with bed rest, adequate fiuid intake, aspirin or acetaminophen (in children) to relieve fever and muscle pain, and guaifenesin or another expectorant to relieve nonproductive coughing. Prophylactic antibiotics are not recommended because they have no effect on the influenza virus.

Amantadine, oseltamivir phosphate, and zanamivir (antiviral agents) have proved to be effective in reducing the duration of signs and symptoms in influenza A infection. In infiuenza complicated by pneumonia, supportive care (fiuid and electrolyte supplements, oxygen, 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 and Prevention Tips for Influenza

• Advise the patient to use mouthwashes and increase fiuid intake. Warm baths or heating pads may relieve myalgia. Provide nonnarcotic analgesics and antipyretics as needed.
• Screen visitors to protect the patient from bacterial infection and the visitor from influenza. Use respiratory precautions.
• Teach the patient proper disposal of tissues and proper hand-washing technique to prevent the virus from spreading.
• Watch for signs and symptoms of developing pneumonia, such as crackles, another temperature rise, and coughing accompanied by purulent or bloody sputum. Assist the patient in a gradual return to normal activities.
• Educate patients about influenza immunizations. Although the vaccine has not been proven harmful to the fetus, it's not recommended for pregnant women during the first trimester.
• Children older than 8 months may safely receive the vaccine in reduced doses. For people who are hypersensitive to eggs, amantadine is an effective alternative to the vaccine.