What is Influenza?

Influenza is an acute, highly contagious respiratory infection caused by any of several closely related viruses. There are three major groups of these viruses, designated A, B, and C. Major influenza epidemics are usually caused by a strain of the A virus.

Q: What are the symptoms of influenza?

A: After an incubation period of about two days, there is a sudden onset of shivering, called a chill; headache; weakness and fatigue; aching in the muscles and joints; a sore throat; a dry, painful cough; and general malaise. There may also be vomiting and an aversion to light and noise. Initially, the body temperature may rise to about 104F (40C), dropping to between 102F (38C) and 103F (39C) for two or three days, then settling at between 100F (37.5C) and 102F (38C). As the illness progresses, the cough may become less dry and painful because of the production of sputum. If no complications develop, the fever generally lasts for about five days. Recovery is usually rapid and without relapse, although it may be accompanied by some weakness and depression.

Q: Can influenza have any complications?

A: Yes. Influenza lowers the body's resistance to infection. This makes the patient vulnerable to invasion by other organisms that may cause secondary infections, especially of the lungs and bronchial tubes, sinuses, and ears, causing such conditions as pneumonia, bronchitis, sinusitis, and otitis media. Pneumonia is by far the most serious complication, since it is often fatal in elderly people and in patients with heart and lung diseases or malignancies. Secondary pneumonia is the major cause of death related to influenza in economically developed countries.

Q: How is influenza treated?

A: The patient should go to bed as soon as symptoms appear and should remain there until a complete recovery has been made. The patient should drink plenty of fluids, especially while there is a fever. Acetaminophen may help to relieve muscle and joint pains and to reduce fever. Aspirin should not be taken by children or young adults suffering from influenza, since it can cause a fatal reaction called Reye's syndrome. The patient should be isolated, both to prevent the spread of infection and to reduce the risk of secondary infections. If any complications develop, a physician should be consulted. Antibiotics are often prescribed to treat secondary complications. Amantadine hydrochloride and a new agent called rimantidine hydrochloride are effective and recommended for the prevention of influenza in individuals exposed to the virus during outbreaks and may help in treating severe cases of influenza.

Q: Can influenza be prevented?

A: Injections of dead influenza virus may confer immunity to that particular strain of influenza. The vaccination is neither immediately nor totally effective; it confers immunity about 7 days after injection and protects about 70 percent of those immunized. But the influenza virus tends to change and produce new strains; vaccination with one strain, therefore, does not give immunity to all of them. For this reason, vaccinations must be given each year as new strains develop. Vaccinations are usually given in the fall to confer maximum protection during the winter months. They are recommended for people over age 65 and those with chronic diseases. Experiments have been performed using a modified live virus, but these have not proved as effective as vaccinations with the dead virus.

The drugs amantadine hydrochloride [Symmetrel] and rimantidine hydrochloride have proved useful in preventing respiratory infections due to the A2 strain of influenza virus. Amantadine hydrochloride should not, however, be used by pregnant women; it causes severe temporary dizziness.

Q: How does influenza spread?

A: Influenza is a contagious disease. It is spread by inhaling infected droplets in the air, which are produced by coughing and sneezing. It is also spread when nasal secretions are spread hand-to-hand, and then the infected hand touches mucosal or conjunctival surfaces. Influenza is most common during winter.