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Definition

Usually referred to as the flu or grippe, influenza is a highly infectious respiratory disease caused by certain strains of influenza virus. When the virus is inhaled it attacks cells in the upper respiratory tract causing typical flu symptoms such as fatigue, fever and chills, hacking cough, and body aches. Influenza victims are also susceptible to potentially life-threatening secondary infections. Although the stomach or intestinal upsets and diarrhea are commonly called "flu," the influenza virus rarely causes gastrointestinal symptoms. Such symptoms are most likely due to other organisms such as rotavirus, Salmonella, Shigella, or Escherichia coli.

Description

Influenza is considerably more debilitating than the common cold. Influenza outbreaks occur suddenly and infection rapidly spreads. The annual death toll attributable to influenza and its complications averages 20,000 in the United States alone.

Influenza outbreaks occur on a regular basis. Pandemics, the most serious outbreaks, affect millions of people worldwide and last for several months. The 1918–1919 influenza outbreak serves as the primary example of an influenza pandemic. In that Spanish flu pandemic, the death toll reached a staggering 20–40 million people worldwide. Approximately 500,000 of these fatalities occurred in the United States. Pandemics also occurred in 1957 and 1968 with the Asian flu and Hong Kong flu, respectively. The Asian flu was responsible for 70,000 deaths in the United States, while the Hong Kong flu killed 34,000 people.

Epidemics are widespread regional outbreaks that occur every two to three years and affect 5–10% of the population. The Russian flu in the winter of 1977 is an example of an epidemic. A regional epidemic is shorter lived than a pandemic, lasting only several weeks. Finally, there are smaller outbreaks each winter that are confined to specific locales.

The earliest existing descriptions of influenza were written nearly 2,500 years ago by the ancient Greek physician, Hippocrates. Historically, influenza was ascribed to a number of different agents, including "bad air" and several different bacteria. It was not until 1933 that the causative agent was identified as a virus.

There are three types of influenza viruses, identified as A, B, and C. Influenza A can infect a range of species, including humans, pigs, horses, and birds, but only humans are infected by types B and C. Influenza A is responsible for most flu cases, while infection with types B and C viruses are less common and cause a milder illness.

Causes and symptoms

Approximately one to four days after infection with the influenza virus, a person is hit with an array of symptoms. "Hit" is an appropriate term, because symptoms are sudden, harsh, and followed by overall bodily aches and a fever that may run as high as 104°F (40°C). As the fever subsides, nasal congestion and a sore throat become noticeable. Persons with the flu feel extremely tired and generally miserable. Typical influenza symptoms include the abrupt onset of a headache, dry cough, and chills, and a rapid onset of physical weakness. Normal energy levels typically do not return for several days, but this can extend up to two weeks.

Influenza complications usually arise from secondary bacterial infections of the lower respiratory tract. Signs of a secondary respiratory infection often appear just as a person seems to be recovering. These signs include high fever, intense chills, chest pains associated with breathing, and a productive cough with thick, yellowish-green sputum. If these symptoms appear, medical treatment is necessary. Other secondary infections, such as sinus or ear infections, may also require medical intervention. Heart and lung problems and other chronic diseases can be aggravated by influenza. This is a particular concern among elderly people.

With children and teenagers, it is advisable to be alert for symptoms of Reye's syndrome, a rare but serious complication of the flu. Symptoms of Reye's syndrome are nausea and vomiting, and—more seriously— neurological problems such as confusion or delirium. Among children Reye's syndrome can be fatal. The syndrome has been associated with the use of aspirin to relieve flu symptoms.

Diagnosis

Although specific laboratory tests can be performed on respiratory samples to identify a flu virus strain, doctors typically rely on a set of symptoms and the presence of influenza in the community for diagnosis. Specific tests are useful to determine the type of flu in the community, but they do little to influence individual treatment. Doctors may administer tests, such as throat cultures, to identify and treat secondary bacterial infections.

Treatment

Essentially, little can be done for a case of influenza an it must simply run its course. Symptoms can be relieved with bed rest and by keeping well hydrated. A steam vaporizer may make breathing easier, and pain relievers such as ibuprofen and acetaminophen will relieve most aches and pains. Food may not seem appetizing, but an effort should be made to consume nourishing food. Returning to normal activities too quickly invites a possible relapse or complications.

Drugs

Since influenza is a viral infection, antibiotics are not an effective treatment. However, antibiotics are frequently used to treat secondary infections. Over-thecounter medications are used to treat symptoms, but it is not necessary to purchase a product marketed specifically for flu symptoms. Any medication designed to relieve pain and coughing will provide some relief. Products containing alcohol, however, should be avoided because of the dehydrating effects of alcohol. The best medicine for symptoms is simply an analgesic, such as acetaminophen or ibuprofen. Without a doctor's approval, aspirin is generally not recommended for people under the age of 18 years owing to its association with Reye's syndrome. As a precaution against the syndrome, children should receive acetaminophen or ibuprofen to treat their symptoms.

There are two antiviral drugs marketed for use in the United States against the influenza virus. These may be useful in treating individuals who have weakened immune systems or who are at risk for developing serious complications of influenza but may be allergic to the flu vaccine. The first is amantadine hydrochloride, which is marketed under the names Symmetrel (syrup), Symadine (capsule), and Amantadine-hydrochloride (capsule and syrup). The second antiviral is rimantadine hydrochloride, marketed under the trade name Flumandine (tablet and syrup). These two drugs are chemically related and are only effective against type A influenza viruses. Both drugs can cause side effects such as nervousness, anxiety, lightheadedness, and nausea. Side effects are more likely to occur with amantadine. Severe side effects include seizures, delirium, and hallucinations. These are rare and are nearly always limited to people who have kidney problems, seizure disorders, or psychiatric disorders.

Alternative treatment

There are several alternative treatments that may help in fighting off the virus, easing symptoms, and promoting recovery:

• • Acupuncture and acupressure. Both are said to stimulate natural resistance, relieve nasal congestion and headaches, fight fever, and calm coughs, depending on the acupuncture and acupressure points used.
• • Aromatherapy. Aromatherapists recommend gargling daily with one drop each of the essential oils of tea tree (Melaleuca spp.) and lemon mixed in a glass of warm water. If the patient is already suffering from the flu, two drops of tea tree oil in a hot bath may help ease the symptoms. Essential oils of eucalyptus (Eucalyptus globulus) or peppermint (Mentha piperita) added to a steam vaporizer may help clear chest and nasal congestion.
• • Herbal remedies. Herbal remedies such as echinacea can be used to stimulate the immune system; as antivirals, goldenseal (Hydrastis canadensis) and garlic (Allium sativum) can be used. They can also be used to alleviate whatever symptoms arise as a result of the flu. For example, an infusion of boneset (Eupatroium perfoliatum) may counteract aches and fever, and yarrow (Achillea millefolium) or elderflower tinctures may combat chills.
• • Homeopathy. To prevent flu a homeopathic remedy called Oscillococcinum may be taken at the first sign of flu symptoms and repeated for a day or two. Other recommended homeopathic remedies vary according to the specific flu symptoms present. Gelsemium (Gelsemium sempervirens) is recommended to combat weakness accompanied by chills, headache, and nasal congestion. Bryonia (Bryonia alba) may be used to treat muscle aches, headaches, and a dry cough. For restlessness, chills, hoarseness, and achy joints, poison ivy (Rhus toxicodendron) is recommended. Finally, for bodily aches and a dry cough or chills, Eupatorium perfoliatum is suggested.
• • Hydrotherapy. A hot bath to induce a fever will speed recovery from the flu by creating an environment in the body where the flu virus cannot survive. Taking a bath in water as hot as can be tolerated, and remain in the bath for 20–30 minutes, is recommended. While in the bath, drinking a cup of yarrow or elderflower tea helps induce sweating. However, a cold cloth should be held on the forehead or the nape of the neck to keep down the temperature of the brain. In case dizziness or weakness occurs, the patient should be assisted when getting out of the bath. The individual should then go to bed and cover up with layers of blankets to induce more sweating.
• • Vitamins. For adults, 2–3 grams of vitamin C daily may help prevent the flu. Increasing the dose to 5–7 grams per day if infected by the flu can help overcome the infection. The dose of vitamin C should be reduced if diarrhea develops.

Prognosis

Following proper treatment guidelines, healthy people under the age of 65 years of age usually suffer no long-term consequences associated with influenza infections. While the elderly and the chronically ill are at greater risk for secondary infection and other complications, they can also recover completely. While most people fully recover from an influenza infection, the flu should not be viewed with complacency. Influenza is a serious disease. Approximately one in every 1,000 cases proves fatal.

Health care team roles

Family physicians, internists, and pediatricians most often diagnose influenza in people who seek medical attention. Nurse practitioners and physician assistants may also make such diagnoses. A physician usually prescribes over-the-counter products for symptomatic relief. Occasionally, antiviral products are prescribed for people at particular risk. Nurses administer vaccines to prevent influenza, providing education and information to those contemplating or receiving the vaccine.

Prevention

The Centers for Disease Control and Prevention recommend that people—particularly the at-risk population such as children, individuals with other diseases or disorders or a compromised immune system, and the elderly—get an influenza vaccine injection each year before the flu season starts. In the United States the flu season typically runs from late December to early March. Vaccines should be received two to six weeks prior to the beginning of the flu season to allow people's bodies enough time to establish immunity. Adults need only one dose of the yearly vaccine, but children under nine years of age who have not previously been immunized should receive two doses with a month between each dose.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 70–90% effective in people younger than 65 years of age. Because immune response diminishes somewhat with age, people older than 65 years may not receive the same level of protection from the vaccine as do younger people. Even if they do contract the flu, the elderly benefit from vaccines, which diminish severity and help prevent complications.

The virus strains used to make the vaccine are inactivated and will not cause a case of influenza. In the past, flu symptoms following vaccination were associated with vaccine preparations that were not as highly purified as modern vaccines, not to the virus itself. In 1976 there was a slightly increased risk of developing Guillain-Barré syndrome, a very rare disorder associated with the swine flu vaccine. This association occurred only with the 1976 swine flu vaccine preparation and has never recurred.

Serious side effects with modern vaccines are extremely unusual. Some people experience a slight soreness at the point of injection, which resolves within a day or two. People who have never been exposed to influenza, particularly children, may experience one to two days of a slight fever, tiredness, and muscle aches. These symptoms start within 6 to 12 hours after vaccination.

It should be noted that certain people should not receive an influenza vaccine. Infants six months and younger have immature immune systems and will not benefit from the vaccine. Since the vaccines are prepared using hen eggs, people who have severe allergies to eggs or other vaccine components should not receive the influenza vaccine. As an alternative, they may receive a course of amantadine or rimantadine, which are also used as protective measures against influenza. Other people who might receive these drugs are those who have been immunized after the flu season has started or who are immunocompromised, such as people with advanced HIV disease. Amantadine and rimantadine are 70–90% effective in preventing influenza.

Members of certain groups are strongly advised to be vaccinated because they are at-risk for influenza-related complications:

• • all people 65 years and older
• • residents of nursing homes and chronic-care facilities, regardless of age
• • adults and children who have chronic heart or lung problems, such as asthma
• • adults and children who have chronic metabolic diseases, such as diabetes and renal dysfunction, as well as severe anemia or inherited hemoglobin disorders
• • children and teenagers receiving long-term aspirin therapy
• • pregnant women who will be in the second or third trimester during flu season, or women who are nursing
• • anyone who is immunocompromised, including HIV-infected people with CD4 count over 200; people with cancer; organ transplant recipients; and people receiving steroids, chemotherapy, or radiation therapy
• • anyone in contact with people in these groups, such as teachers, care givers, health-care personnel, and family members
• • travelers to foreign countries

An individual need not be in one of the at-risk categories listed above, however, to receive a flu vaccination. Anyone who wants to avoid the discomfort and inconvenience of a case of influenza should receive the vaccine.

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KEY TERMS

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Common cold—A mild illness caused by an upper respiratory virus. Usual symptoms include nasal congestion, coughing, sneezing, throat irritation, and a low-grade fever.

Epidemic—A widespread regional disease out-break.

Guillain-Barré syndrome—Also called acute idiopathic polyneuritis, this condition is a neurologic syndrome that can cause numbness in the limbs and muscle weakness following certain viral infections.

Pandemic—Worldwide or multiregional outbreak of an infection afflicting millions of people.

Reye's syndrome—A syndrome of nausea, vomiting, and neurological problems such as confusion or delirium. It can be fatal in children.

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L. Fleming Fallon, Jr., M.D., Dr.P.H.