Influenza (Flu)

Overview

At least 20 million people, including 500,000 U.S. citizens, died in the 1918 influenza pandemic. Today, as many as 36,000 Americans continue to die each year of what's commonly known as the flu, and more than 200,000 are hospitalized. Most outbreaks in North America occur between October and May. The peak season is usually late December to early March.

Anyone can get influenza, a viral infection that attacks your respiratory system, including your nose, throat, bronchial tubes and lungs. You're especially at risk if you are an older adult, have diabetes, chronic heart or lung disease, or an impaired immune system.

If you're at high risk of getting the flu, your first line of defense is an annual flu vaccine. And if you get the flu, self-care measures can make you more comfortable.

Signs and symptoms

The flu virus attacks your respiratory system. This leads to the symptoms you commonly experience with the flu. Some signs and symptoms, such as a runny nose, sneezing and sore throat, may initially seem like a common cold. But if you are an adult and have a fever of 101 F or more, you may have influenza. Your fever may last from one day to as long as a week and, in rare cases, may reach as high as 106 F.

You're also likely to feel much worse with the flu than with a cold. Although you can probably carry on with a cold, the flu can knock you flat. Even after you've recovered, you may still feel tired.

Other signs and symptoms of influenza include:

• Chills and sweats
• Headache
• Dry cough
• Muscular aches and pains, especially in your back, arms and legs
• Fatigue and weakness
• Nasal congestion
• Loss of appetite

Children with the flu tend to have higher fevers than infected adults have — often 103 to 105 F. Influenza may also cause children to feel nauseous and experience vomiting and diarrhea.

The flu virus typically has an incubation period of one to four days, although symptoms usually come on suddenly. In most cases, you should feel better in about a week to 10 days unless you develop a serious post-flu lung infection, such as bacterial pneumonia or subacute bronchitis — an inflammation of the lining of your bronchial tubes.

If you've been infected with the flu, you can spread the disease to others before you realize you're sick and for as long as a week after your symptoms appear.

Distinguishing flu from other ailments
Although other viral infections, especially colds and intestinal ailments such as gastroenteritis — a condition that causes diarrhea, nausea and vomiting — are often referred to as the flu, they're not. Real influenza usually doesn't affect your intestines. And while you may cough and sneeze with the flu, you're also likely to have a high fever, chills and body aches — signs and symptoms you won't typically have with a cold.

Causes

You're exposed to the flu when someone who's infected with the influenza virus coughs or sneezes, or you touch something they've handled. That's why the flu spreads rapidly anywhere people congregate — schools, child-care centers, offices, nursing homes, buses, even luxury cruise ships.

The flu is caused by three types (strains) of viruses — influenza A, B and C. Type A is responsible for the deadly influenza pandemics (worldwide epidemics) that strike every 10 to 40 years, whereas type B causes smaller, more localized outbreaks. Type C is less common and causes only mild symptoms.

Type C is a fairly stable virus, but types A and B are constantly changing, with new strains appearing regularly. This results in a new epidemic every few years. Localized epidemics involving virulent strains of flu generally occur about every three to 15 years.

Once you've had the flu, you develop antibodies to the virus that caused it, but those antibodies won't protect you from new strains. And although outbreaks in different regions generally vary in their duration and severity, the fact that millions of people travel every day means that regional strains of flu can show up just about anywhere.

Risk factors

Children ages 6 months to 2 years and people older than 65 are considered at high risk of complications from influenza. You're also at increased risk of influenza or its complications if you:

• Are a resident of a nursing home or other chronic-care facility.
• Have a chronic disorder such as diabetes or heart, kidney or lung conditions. People with diabetes are at greater risk of complications of flu, such as pneumonia, and are three times more likely to die of flu than are people without diabetes.
• Have a weakened immune system from infection with the human immunodeficiency virus (HIV), leukemia or medications you take following an organ transplant.
• Will be in your second or third trimester of pregnancy during flu season.
• Work in a health care facility where you're more likely to be exposed to the flu virus.
• Are in regular, close contact with children age 2 or younger.

Children are at high risk if they:

• Have asthma or another chronic lung condition.
• Have cardiovascular disease. Children with cardiovascular disease may have a passive congestion of their lungs, which makes them more susceptible to viral illnesses.
• Are taking medications to suppress their immune systems.
• Have sickle cell anemia, HIV infection, diabetes, chronic kidney disease, chronic metabolic diseases or are on long-term aspirin therapy. Aspirin therapy puts children age 16 and under at risk of Reye's syndrome, a rare but potentially fatal disease.

The flu vaccine is safe for children 6 months or older. If your child isn't at risk of the flu but lives with someone who is — a grandparent, for instance, or anyone with a chronic heart or lung disease, or compromised immune system — you still may want to have your child vaccinated. That way, he or she is less likely to infect others. In fact, the more people who are immunized, the less likely it is that the infection will spread through a community.

When to seek medical advice

See your doctor right away if you have flu symptoms and you're at risk of a severe case of influenza or complications of the disease. For some people, drugs known as neuraminidase inhibitors may help shorten the flu's duration and intensity. Other antiviral drugs, such as amantadine (Symmetrel), may help reduce the duration and severity of type A influenza, but may also cause side effects. To be effective, antiviral drugs need to be taken no later than 24 to 48 hours after you first notice symptoms.

In addition, seek medical help if you have trouble breathing, a severe sore throat, a cough that produces a lot of green or yellow mucus, or you feel faint. See your doctor immediately if you think you might have signs or symptoms of pneumonia. These may include a severe cough that brings up phlegm, a high fever and a sharp pain when you breathe deeply. If you have bacterial pneumonia, you'll need treatment with antibiotics.

Complications

If you're young and healthy, influenza is usually just a moderately severe illness. Although you may feel completely miserable while you have it, flu usually goes away with no lasting effects. But if you're 65 years of age or older or have a chronic illness, signs and symptoms can be much more serious and may lead to complications such as acute sinusitis, bronchitis or pneumonia. Newborn babies also are at increased risk of serious complications.

Pneumococcal pneumonia, a serious bacterial infection of your lungs, is the most common severe complication of influenza. For older adults and people with chronic heart or lung disease, or compromised immune systems, pneumonia can be deadly. The best protection is to be vaccinated against both pneumococcal pneumonia and influenza.

Some people may only need to receive the pneumonia vaccine once. Others, especially those with a serious underlying disease such as AIDS or who have had their spleen removed, may need to be vaccinated again in five to 10 years. Flu vaccines need yearly updates.

Treatment

Unless you're at risk of complications from influenza, your doctor may suggest nothing more than bed rest, plenty of fluids to prevent dehydration, and over-the-counter medicines such as acetaminophen. But in some cases, he or she may also prescribe an antiviral medication, such as:

• Neuraminidase inhibitors. These drugs, which treat both influenza A and B, work by inactivating an enzyme the virus needs to grow and spread. Zanamivir (Relenza) may shorten the amount of time you have the flu by a day or two and may also cut the risk of flu within a family when one family member is infected. Relenza is inhaled through a device similar to an asthma inhaler every 12 hours for five days. It's not for use by anyone with respiratory conditions such as asthma and lung disease. Side effects may include nose and throat discomfort, headache and cough. Another drug, oseltamivir (Tamiflu) is available in pill form. It may also shorten the duration of the flu by a day or so.
• Oral antiviral medications. Drugs such as amantadine (Symmetrel) and rimantadine (Flumadine) may slightly reduce the severity and duration of type A — but not type B — influenza if you take them within 48 hours after symptoms begin. But these medications may have serious side effects, including nausea, lightheadedness, anxiety, difficulty sleeping and nightmares. Taking lower doses of the drugs may reduce side effects.

None of these drugs are useful if you've waited too long to see your doctor for a prescription, however. And if they're not taken as recommended, there's a chance that drug-resistant influenza may develop.

Prevention

To help prevent any illness, eat right, get enough sleep, exercise regularly and wash your hands often. In the case of influenza, you can also protect yourself by getting a flu vaccine each fall. Flu vaccinations need to be updated every year because the strains of viruses that cause the disease change frequently. In addition, if you're at high risk, try to avoid crowds when flu season is at its peak.

The best time to be immunized is in October or November. This allows your immunity to peak during the height of the influenza season, which is generally December through March. Adults receive the vaccine in one injection. Children younger than age 9 who are receiving the vaccine for the first time need two separate injections about a month apart. It takes one to two weeks after you've been vaccinated for the shot to take effect.

Effectiveness of vaccine varies
The flu vaccine isn't foolproof. Its effectiveness varies based on the length and intensity of each flu season and the health of each person vaccinated. Because the strains used in the vaccine are chosen nine months before a particular flu season, there's a slight chance the strains may change before the flu season actually starts. All of these factors make the degree to which the vaccine works difficult to measure.

Still, if you're young and healthy, the vaccine may be 70 percent to 90 percent effective in preventing illness. If you are an older adult or have a chronic medical condition, the vaccine may not be as protective against influenza, but numerous studies have shown that it significantly reduces your risk of flu-related complications and hospitalizations.

The Centers for Disease Control and Prevention (CDC) recommends flu shots for:

• Children ages 6 months to 2 years, as well as their caregivers and close household contacts
• Adults age 50 and older
• Women who will be pregnant during flu season
• Children on chronic aspirin therapy
• People ages 2 to 64 with an impaired immune system or a serious illness such as chronic heart or lung disease, kidney disease, diabetes, or sickle cell anemia
• People living in nursing homes or long term care facilities
• Health care workers who have direct patient contact

Flu shot won't give you the flu
You may worry about contracting flu from the shot. But the injected vaccine is made from an inactivated form of the virus, so you can't get the flu from a flu shot. In some cases, however, you may have a slight reaction to the shot, such as soreness at the injection site, mild muscle aches or fever beginning six to 12 hours after you've been immunized. These symptoms may last one to two days and are more likely to occur in children who've never been exposed to the flu virus.

If you're allergic to eggs, you probably shouldn't have a flu shot. Because the viruses are grown in chicken eggs, you may have an allergic reaction. If you're pregnant, wait until after your first trimester to be immunized, unless your doctor advises you otherwise.

FluMist is an option
Healthy people ages 5 to 49 also may receive the flu vaccine through a nasal spray form called FluMist. It protects against the same strains of influenza that the flu shot does. Like the flu shot, FluMist has to be given every year.

FluMist is a live vaccine, which means it contains live influenza virus. Some people who get the vaccine, especially children, shed the virus through nasal secretions. For this reason, it's theoretically possible for a person who has received the live vaccine to transmit the vaccine virus to other people. But this has happened rarely in clinical studies.

FluMist is not recommended for:

• Children younger than age 5 and adults older than age 50
• Pregnant women
• People with chronic conditions such as diabetes or asthma
• People with impaired immune systems
• Children on aspirin therapy
• People with a history of Guillain-Barre syndrome
• People with an allergy to chicken eggs
• Health care workers who care for patients with severely compromised immune systems

In addition to getting a flu vaccine from your doctor, you can be vaccinated at public health centers and many pharmacies. In some areas, flu vaccines are also available at senior or community centers.

Self-care

If you do come down with the flu, these measures may help ease your symptoms:

• Drink plenty of liquids. This will help you to avoid dehydration.
• Rest up. Get more sleep.
• Try chicken soup. It's not just good for your soul — it really can help relieve flu symptoms by breaking up congestion.
• Take pain relievers. Use an over-the-counter pain reliever such as acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin, others) cautiously, as needed. Remember, pain relievers may make you more comfortable, but they won't make your symptoms go away any faster and may have serious side effects. Ibuprofen may cause stomach pain, bleeding and ulcers. If taken for a long period of time or in high doses, acetaminophen can be toxic to your liver. Talk to your doctor before giving acetaminophen to children — it may cause liver or kidney damage. And don't give aspirin to children under age 16 because of the risk of Reye's syndrome, a rare but potentially fatal disease.