The flu, also called influenza, is an infection of the nose, throat, and lungs, which are part of the respiratory system. The flu is caused by a virus. Influenza viruses are different from the viruses that cause viral gastroenteritis, which leads to diarrhea and vomiting.
Most people with the flu recover on their own. However, in some cases, the illness and its complications can be deadly. To protect yourself against seasonal influenza, you can get the flu vaccine every year. Although the vaccine is not 100% effective, it reduces the risk of serious complications from the infection. This is especially important for individuals at high risk of flu complications.
In addition to getting vaccinated, there are other steps you can take to help prevent flu infection. You can clean and disinfect surfaces, wash your hands regularly, and ensure good air circulation in your surroundings.
Symptoms
Flu viruses spread at higher levels during certain times of the year in the Northern and Southern Hemispheres. These times are referred to as flu seasons. In North America, the flu season typically occurs between October and May.
Common flu symptoms include a sore throat and nasal congestion or runny nose. These symptoms can also occur with other illnesses, such as the common cold. However, colds usually begin slowly, while the flu tends to come on suddenly, about two or three days after exposure to the virus. And while a cold can be annoying, the flu generally makes you feel much worse.
Other common flu symptoms include:
-
Fever
-
Cough
-
Headache
-
Muscle aches
-
Feeling very tired
-
Sweating and chills
In children, these symptoms may present more generally as restlessness or irritability. Children are also more likely than adults to experience ear pain, stomach discomfort, vomiting, or diarrhea with the flu.
In some cases, people may experience eye pain, watery eyes, or sensitivity to light.
When to See a Doctor
Most people with the flu can manage the condition at home and often do not need to see a healthcare professional.
If you have flu symptoms and are at risk of complications, see a healthcare provider right away. Taking antiviral medications within two days of symptom onset can shorten the duration of the illness and help prevent serious problems.
If your flu symptoms suggest an emergency, seek medical attention immediately. In adults, emergency symptoms may include:
-
Difficulty breathing or shortness of breath
-
Chest pain or pressure
-
Persistent dizziness
-
Trouble waking up or confusion
-
Dehydration
-
Seizures
-
Worsening of existing medical conditions
-
Severe weakness or intense muscle pain
In children, emergency symptoms include all of the above, plus the following:
-
Fast breathing or ribs pulling in with each breath
-
Bluish or gray lips or nail beds
-
No tears when crying, dry mouth, and no need to urinate
-
Symptoms like fever or cough that improve but then return or worsen
Causes
The flu is caused by viruses. These viruses travel through the air in droplets when someone with the infection coughs, sneezes, or talks. You can breathe in these droplets directly. You can also become infected by touching an object, like a computer keyboard, and then transferring the virus to your eyes, nose, or mouth.
You can spread the flu virus to others starting about one day before symptoms appear and up to five to seven days after symptoms begin. This period is known as being contagious. Children and people with weakened immune systems may be contagious for a slightly longer time.
Influenza viruses constantly change, and new strains frequently appear.
A person’s first flu infection offers some long-term protection against similar strains. However, the vaccines offered each year are designed to match the flu strains most likely to circulate during that season. The protection from these vaccines typically lasts several months for most people.
Risk Factors
Several factors can increase the risk of getting the flu virus or experiencing complications from it:
Age (young or elderly):
Seasonal flu tends to have more severe outcomes in young children, particularly those under 2 years of age. Adults over 65 also tend to have worse outcomes.
Living conditions:
People living in group facilities, such as nursing homes and long-term care centers, are more likely to catch the flu.
Weakened immune system:
A weak immune system may not be able to quickly eliminate the flu virus, increasing the risk of catching the flu or having complications. Immune systems may be weak from birth, illness, or as a result of treatments or medications.
Chronic health conditions:
Chronic conditions can increase the risk of flu-related complications. Examples include asthma and other lung diseases, diabetes, heart and neurological diseases, a history of stroke, metabolic disorders, airway issues, and kidney, liver, or blood diseases.
Race or ethnicity:
In the United States, Native Americans, Alaska Natives, Black individuals, and Hispanic/Latino individuals may have a higher risk of needing hospitalization for flu-related care.
Aspirin treatment:
Children and teens receiving long-term aspirin therapy are at risk of developing Reye’s syndrome if they contract the flu.
