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Flu (virus not identified)

Also known as: Influenza, virus not identified

General information only. Anpheros does not diagnose and does not recommend treatment. Talk to a doctor or pharmacist about your situation. In an emergency, call 112 (or your local emergency number).

In short

Influenza, also known as the flu, is a respiratory infection caused by viruses that spread from person to person through droplets or by touching contaminated surfaces. Symptoms of the flu typically start suddenly and can include fever, cough, sore throat, runny or stuffy nose, muscle aches, headaches, and fatigue. While the illness can be mild, it can also lead to serious or life-threatening complications such as bronchitis, ear or sinus infections, pneumonia, and inflammation of the heart, brain, or muscle tissues. Most individuals recover on their own without medical care, but those with mild cases should stay home and avoid contact with others.

Source: MedlinePlus, National Library of Medicine.

AI-generated summary of the sources cited on this page, checked automatically against them. Not reviewed by a clinician; not medical advice.

Codes

ICD-10: J11
ICD-11: 1E32 Influenza, virus not identified

Description

What is the flu?
The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses.
What causes the flu?
The flu is caused by flu viruses that spread from person to person. When someone with the flu coughs, sneezes, or talks, they spray tiny droplets. These droplets can land in the mouths or noses of people who are nearby. Less often, a person may get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.
What are the symptoms of the flu?
Symptoms of the flu come on suddenly and may include:
Fever or feeling feverish/chills
Cough
Sore throat
Runny or stuffy nose
Muscle or body aches
Headaches
Fatigue (tiredness)
Some people may also have vomiting and diarrhea. This is more common in children.
Sometimes people have trouble figuring out whether they have a cold or the flu. There are differences between them:
Signs and Symptoms
Cold
Flu
Start of symptoms
Slowly
Suddenly
Fever
Rarely
Usually
Aches
Sometimes (slight)
Usually
Fatigue, weakness
Sometimes
Usually
Headache
Rarely
Common
Stuffy nose, sneezing, or sore throat
Common
Sometimes
Sometimes people say that they have a "flu" when they really have something else. For example, "stomach flu" isn't the flu; it's gastroenteritis.
What other problems can the flu cause?
Some people who get the flu will develop complications. Some of these complications can be serious or even life-threatening. They include:
Bronchitis
Ear infection
Sinus infection
Pneumonia
Inflammation of the heart (myocarditis), brain (encephalitis), or muscle tissues (myositis, rhabdomyolysis)
The flu also can make chronic health problems worse. For example, people with asthma may have asthma attacks while they have flu.
Certain people are more likely to have complications from the flu, including:
Adults 65 and older
Pregnant women
Children younger than 5
People with certain chronic health conditions, such as asthma, diabetes, and heart disease
How is the flu diagnosed?
To diagnose the flu, health care providers will first do a medical history and ask about your symptoms. There are several tests for the flu. For the tests, your provider will swipe the inside of your nose or the back of your throat with a swab. Then the swab will be tested for the flu virus.
Some tests are quick and give results in 15-20 minutes. But these tests are not as accurate as other flu tests. These other tests can give you the results in one hour or several hours.
What are the treatments for the flu?
Most people with the flu recover on their own without medical care. People with mild cases of the flu should stay home and avoid contact with others, except to get medical care.
But if you have symptoms of flu and are in a high risk group or are very sick or worried about your illness, contact your health care provider. You might need antiviral medicines to treat your flu. Antiviral medicines can make the illness milder and shorten the time you are sick. They also can prevent serious flu complications. They usually work best when you start taking them within 2 days of getting sick.
Can the flu be prevented?
The best way to prevent the flu is to get a flu vaccine every year. But it's also important to have good health habits like covering your cough and washing your hands often. This can help stop the spread of germs and prevent the flu.
Centers for Disease Control and Prevention

Source: MedlinePlus, National Library of Medicine.

Next to it in ICD-10

Neighbouring codes in the classification, not a medical link.

External resources

Questions

What is the ICD-10 code for Flu (virus not identified)?

J11 (WHO, International Classification of Diseases, 10th Revision).

What is the ICD-11 code for Flu (virus not identified)?

1E32: Influenza, virus not identified (WHO, ICD-11 for Mortality and Morbidity Statistics).

Sources and attribution

Names other than the official source titles: Anpheros translations and plain-language names, made with AI assistance and checked automatically; the source names are in English.
Source: MedlinePlus, National Library of Medicine.
ICD-10 codes and titles © World Health Organization. Source: WHO, International Classification of Diseases, 10th Revision (2019).

Anpheros Search catalog 2026.10.5, published 17 October 2026. About the data →

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