Flu (influenza) is a contagious illness caused by the influenza viruses. There are a variety of infuenza viruses that cause similar symptoms that range from mild to life-threatening.
Most healthy people recover from the flu without problems, but certain people are at high risk for serious complications.
Those at risk of developing severe complications include the elderly, young children, pregnant women and people with other health conditions, such as asthma, diabetes, or heart disease.
The best way to prevent seasonal flu is by getting a seasonal flu vaccination each year.The Centers for Diseae Control (CDC) recommends that everyone 6 months and older should get a flu vaccine each year.
Timing of Flu Season
The timing and duration of flu seasons vary each year. Seasonal outbreaks of the flu can start as early as October. Flu cases tend to peak around January, but can continue into Spring. (People traveling to other countries should be aware that the flu may occur at different times, and may need to begin country-specific vaccinations several months before travel.)
In the U.S., 5-20% individuals get the flu each year and more than 200,000 people are hospitalized from flu-related complications.
The influenza viruses that cause most cases of the flu are categorized as influenza type A or type B. Influenza type B does not change much over time, but type A can mutate rapidly. These changes to the influenza A viruses allow the virus to bypass a person's immune system even if the person has already been sick with the flu or previously received a flu vaccine. As a result, a new version of the flu vaccine must be developed each year to protect people against the flu virus strains that are expected to be prevalent for that year.
Symptoms of Flu
Symptoms of seasonal flu include:
- Fever or feeling feverish/chills.It is important to note that not everyone with flu will have a fever.
- Fatigue, often extreme
- Dry cough
- Sore throat
- Runny or stuffy nose
- Muscle aches
Stomach symptoms, such as nausea, vomiting, and diarrhea, also can occur but are more common in children than adults.
Is it a Cold or the Flu?
The flu and the common cold are both infectious diseases that can cause similar symptoms, such as cough, congestion and sore throat. Though they are caused by different viruses, it can be difficult to determine whether a person has a bad cold or is suffering from the flu.
In general, the flu is worse than the common cold. People with colds are more likely to have a runny or stuffy nose as their primary symptom. Symptoms such as fever, body aches, extreme tiredness, and dry cough are more common and intense with the flu. Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations.
A flu test can be performed within the first few days of the illness to determine it is due to an influenza virus, but this is usually not necessary.
Complications of Flu
Complications of flu can include bacterial pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.
How Flu Spreads
The flu spreads from person to person.
People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses are spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth or nose.
To avoid becoming infected, people should wash their hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub. Linens, eating utensils, and dishes belonging to those who are sick should not be shared without washing thoroughly first. Eating utensils can be washed either in a dishwasher or by hand with water and soap and do not need to be cleaned separately.
Most healthy adults may be able to infect others beginning 1 day BEFORE symptoms develop and up to 5-7 days after becoming sick. That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick.
Reference: Centers for Disease Control and Prevention
- Show All