Influenza, or "flu," is a common infection caused by a virus affecting the respiratory tract (like the nose and upper airways). Its symptoms are usually more severe than the common cold and are more likely to affect other parts of your body like your stomach and muscles. The flu is very contagious – spreading easily from one person to the next. While most cases run their course in one to two weeks, life-threatening complications such as pneumonia are possible, especially in the elderly or people with chronic illnesses.

• Fever that comes on suddenly (101 to 104 F)
• Chills
• Headache
• Muscle aches
• Fatigue
• Nonproductive cough
• Sore throat
• Sneezing, runny nose, stuffy nose
• Loss of appetite
• Nausea, vomiting, or diarrhea, especially in children

Influenza is caused by viruses that are spread through the air by sneezes and coughs. Some of these viruses cause a very mild illness, or none at all. Others cause serious, widespread illness.

Since there are many types of influenza virus, and because they change over time, a new flu vaccine is offered every fall. Getting vaccinated before the flu season starts reduces your chances of getting the flu, and reduces its severity if you do get it. You should not take the vaccine if you have an allergy to eggs, as influenza viruses for the vaccines are grown in chick embryos. See Risk Factors for list of people who should get the vaccine every year.

People most likely to get influenza are those whose immune systems are not working properly (for example, transplant recipients or people with HIV), or those whose lifestyle or work brings them into frequent contact with sick people (like health care workers).

The following put you at greatest risk for complications from influenza:

• Age over 50
• Having a serious underlying medical condition like diabetes, heart disease, lung disease (such as asthma or cystic fibrosis), or kidney disease
• Having a weakened immune system (see description above).

If you are at risk for complications, you should receive the vaccine annually (see Prevention).

Your health care provider will probably be able to diagnose your case of flu from a physical examination and a description of your symptoms. He or she may take a chest X ray if there is concern about complications such as pneumonia.

Annual flu shots are recommended if you:

• Are 50 years of age or older
• Have chronic heart, lung, or kidney disease
• Live in an institution (such as a nursing home)
• Have a weakened immune system
• Have sickle cell anemia

You should not receive the vaccine if you are allergic to eggs.

The most important aspect of treatment is rest and fluids. Taking mild pain medication, available without a prescription, can help relieve muscle aches and pains. If you are at high risk for complications (see Risk Factors), then antiviral medications (drugs that fight the virus) may shorten the duration of your symptoms, but they need to be started within 48 hours of the start of the illness. Certain herbs, supplements, and homeopathic remedies may help some of your symptoms and acupuncture may help reduce fever.

• Drink a lot of water
• Rest to restore your energy and avoid complications like pneumonia.
• Eat a diet rich in fresh fruits and vegetables. These foods provide lots of antioxidants (substances that may help boost your immune system), especially vitamins A and C.
• Exercise regularly, which may diminish your chances of getting the flu and may improve your response to the vaccine.
• Minimize your stress and your reaction to stress. Consider yoga, tai chi, or other forms of relaxation on an ongoing basis. Stress can put you at increased risk for viruses like influenza.

• Acetaminophen, aspirin, or ibuprofen — for fever reduction and relief of minor aches and pain. Note: aspirin should NEVER be given to children with a viral illness because of the risk of a life-threatening disease called Reye's syndrome which can affect the liver and brain.
• Antiviral medications—amantidine and rimantadine for prevention and treatment of certain types of flu; zanamivir and oseltamivir to reduce the symptoms and duration of flu

Because supplements may have side effects or interact with medications, they should be taken only under the supervision of a knowledgeable healthcare provider. Be sure to talk to your physician about any supplements you are taking or considering taking.

Lactobacillus acidophilus

Lactobacillus is a probiotic, which means that it is an organism that actually helps fight, rather than cause, infection. Studies have been quite promising in terms of the ability of lactobacillus supplements or lactobacillus in certain milk and yogurt products to help reduce the likelihood of getting a respiratory infection, like the flu, even in children. Talk to your doctor or pediatrician about possibly trying lactobacillus to prevent infections.

Spirulina

Spirulina is widely used to enhance immune function. In support of this popular use are test tube studies that suggest that Spirulina has activity against influenza. Whether this laboratory finding will prove beneficial for people in treating this infection is not yet clear.

Vitamin C

Despite the popular belief that vitamin C can cure a cold and the flu, the scientific evidence supporting this idea is limited. There have been a few studies suggesting that taking large doses of vitamin C supplements at the onset of cold or flu symptoms, or just after exposure to someone with one of these ailments, can shorten the duration of the illness or ward it off altogether. However, the majority of studies, when looked at collectively, lead researchers to conclude that vitamin C does not prevent or treat flu.

If that is the case, however, why do so many stand strongly by the belief that it works? Some experts suggest that vitamin C may only be useful in case of the flu if you have low levels of this nutrient to begin with. Another possibility is that the likelihood of success may be very individual – some improve, while others do not.

Talk to your doctor about any pros and cons with regards to using vitamin C during cold and flu season.

Zinc

Zinc plays an important role in the immune system, which may explain why it seems to be helpful in protecting against infections like influenza. People who are zinc deficient tend to be more susceptible to a variety of infections. Zinc supplementation enhances immune system activity and protects against a range of infections including colds and upper respiratory infections (like influenza). Several important studies, but not all, have revealed that zinc lozenges may reduce the intensity of the symptoms associated with cold and flu, particularly cough, and the length of time that the symptoms linger. Similarly, nasal zinc gel seems to shorten the duration of the virus. However, zinc nasal spray does not appear to have the same benefit.

The use of herbs is a time-honored approach to strengthening the body and treating disease. Herbs, however, contain active substances that can trigger side effects and interact with other herbs, supplements, or medications. For these reasons, herbs should be taken with care and only under the supervision of a practitioner knowledgeable in the field of herbal medicine. Be sure to also talk to your physician about any herbs that you are taking or considering taking.

Astragalus (Astragalus membranaceus)

Astragalus has been used traditionally to enhance the immune system, including possibly preventing and treating colds and flus. Some practitioners claim that this herb shortens the duration of these viral illnesses, although science has not proven this. Astragalus should not be used if you are taking certain medications for HIV or other viruses.

Celery seed (Apium graveolens)

Celery seed is one of the lesser-known herbs in Western herbal medicine. In other parts of the world, however, it has been used for thousands of years for a variety of reasons including by Ayurvedic physicians (practitioners who practice Ayurvedic medicine, an ancient Indian from of health care) to treat colds and flus.

Echinacea (Echinacea purpurea)

One of the most popular herbs in America today is the Native American medicinal plant known as Echinacea (also called coneflower). Echinacea is primarily used to reduce the symptoms and duration of the common cold and the flu, such as sore throat (pharyngitis), cough, and fever. Although the data in the medical literature goes back and forth somewhat, certain scientific studies do support that Echinacea will have this effect if you start taking it soon after your cold or flu symptoms begin. Science does not support the use of Echinacea before you have a cold or flu, however. In other words, to date, research suggests that this herb does not help prevent colds and flus (despite the popularity of this use), but it does support that it helps treat them if taken early enough.

Elderberry (Sambucus nigra.)

Some early scientific evidence shows that a standardized extract of elderberry can enhance immune function, including in people who have influenza. Although more research is needed, it may also reduce the number of days that you have symptoms from the flu to 3 to 4 from 7 to 14.

Eucalyptus (Eucalyptus globulus)

Eucalyptus is commonly used in remedies to treat the symptoms of cold or flu, particularly cough. It can be found in many lozenges, cough syrups, and vapor baths throughout the United States and Europe. Herbalists recommend the use of fresh leaves in teas and gargles to soothe sore throats. Ointments containing eucalyptus leaves are also applied to the nose and chest to relieve congestion. Eucalyptus oil helps loosen phlegm, so many herbal practitioners recommend inhaling eucalyptus vapors to help treat coughs and the flu. Teas containing eucalyptus leaves have also been used traditionally to reduce fevers.

Goldenrod (Solidago virgaurea)

Goldenrod is used by herbalists for a wide range of health problems including colds and flus.

Goldenseal (Hydrastis canadensis)

Goldenseal is often combined with echinacea in preparations designed to strengthen the immune system. Many professional herbalists recommend goldenseal in herbal remedies for colds and flu. Goldenseal has not been thoroughly investigated in scientific studies, however.

Pau d'arco (Tabebuia avellanedae)

Pau d'arco, or the inner bark of the Tabebuia avellanedae tree, is native to Brazil and has been used traditionally to treat a wide range of conditions including fever. For this reason, some herbalists may recommend the use of this herb as part of your treatment for the flu.

Peppermint (Mentha x piperita)

Peppermint is widely used for cold and flu symptoms. This is because peppermint and its main active agent, menthol, are effective decongestants. Peppermint is soothing and calming for sore throats (pharyngitis) and dry coughs as well.

Siberian ginseng (Eleutherococcus senticosus/Acanthopanax senticosus)

Siberian ginseng may help the body deal with physically and mentally stressful exposures such as viruses that cause the flu. By strengthening your system, it may, in theory, also help prevent viral illnesses. In fact, a 4-week study of healthy people found that those who received Siberian ginseng extract had improvements in a number of measures that reflect the functioning of the immune system. Also, in laboratory studies, an extract of Siberian ginseng slowed the replication of certain viruses, including influenza A (which causes the flu) as well as human rhinovirus and respiratory syncytial virus (both of which cause symptoms of the common cold). These findings don't guarantee that you will be less likely to develop colds and flus if you take Siberian ginseng, but they do suggest that that is possible. More research to test this idea would be interesting.

For some individuals, as reported in the medical literature, acupuncture can help bring down fever when you have the flu.

Although very few studies have examined the effectiveness of specific homeopathic therapies, professional homeopaths may consider the following remedies for the treatment of the flu based on their knowledge and experience. Before prescribing a remedy, homeopaths take into account a person's constitutional type. A constitutional type is defined as a person's physical, emotional, and psychological makeup. An experienced homeopath assesses all of these factors when determining the most appropriate treatment for each individual.

• A combination remedy including Aconite, Gelsemium, Eucalyptus, Ipecacuanha, Phosphorus, Bryonia, and Eupatorium perfoliatum 
• A mixture of Anas barbarice hepatis and Cordis extractum 
• Gelsemium -- for chills, weakness, lack of energy, fever, and headaches in the back and top of the head; this is one of the most common homeopathic remedies for the flu
• Eupatorium perfoliatum -- for deep aches, sneezing and coughing
• Nux vomica -- for violent vomiting, irritability, dry cough, chills, and a stuffy nose that develops into a watery, irritating discharge

If you are in any of the high risk groups described earlier in the section entitled Risk Factors, be sure to call your doctor at the earliest signs of flu symptoms. The sooner you are treated, the less likely you are to develop complications.

As stated earlier, most healthy individuals get over the flu in one to two weeks. For those at high risk as described in the section called Risk Factors, certain serious, even life-threatening, complications can occur including:

• Pneumonia
• Encephalitis (an infection of the brain)
• Secondary bacterial infection elsewhere in the body

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