Influenza (Flu)

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 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 1 month.

Although influenza affects all age groups, its incidence is highest in schoolchildren. Its severity is greatest in the very young, elderly people, and those with chronic diseases. 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

There are three different strains of the influenza virus, called A, B, and C, that are responsible for outbreaks of the flu. However, most flu cases are caused by influenza A. The influenza B and C viruses are less common and cause an illness with milder symptoms. The virus is inhaled, usually by being near an infected person who coughs or sneezes. It can also be caught by touching something that has been contaminated by an infected person's secretions. The virus attacks cells in the upper respiratory tract.

Signs and symptoms

After an incubation period of 24 to 48 hours, flu 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.

Complications

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

At the beginning of an influenza epidemic, early cases are usually mistaken for other respiratory disorders. Because signs and symptoms are not pathognomonic, isolation of M. influenzae 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

Uncomplicated influenza is treated with bed rest, adequate fluid 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 (an antiviral agent) has proved to be effective in reducing the duration of signs and symptoms in influenza A infection. In influenza complicated by pneumonia, supportive care (fluid 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.

Check out the home remedies for influenza.

Prevention

Although there's no guaranteed way - including the vaccine - to prevent anyone from getting the flu, the most simple step you can take is to avoid large crowds. Since it's often nearly impossible to keep kids cooped up, here are some other things you and your family can do to help prevent the spread of infections like the flu:

• Wash your hands thoroughly and frequently.
• Never pick up used tissues.
• Never share cups and eating utensils until you're better.
• Stay home from work or school when you're sick with the flu.
• Cover your mouth and nose with a tissue when you cough or sneeze.