Flu (Influenza) Symptoms: Learn more about the many causes of the flu with the Symptom Checker

Flu Symptoms

Symptom Checker: Symptoms & Signs Index

Medical Editor: Melissa Conrad Stöppler, MD

The flu (influenza) is a viral disease of the respiratory tract caused by influenza viruses. Characteristic symptoms are fever, cough, malaise, and headache. Other symptoms can occur, like nausea and vomiting, muscle aches, sore throat, and diarrhea. Symptoms of the flu usually last for 1-2 weeks.

Other conditions can sometimes cause similar symptoms, leading people to wonder if they really have the flu or a different condition. Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until the virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children and can sometimes cause sinus or other infections. Other bacterial or viral infections, including the common cold, may cause symptoms similar to the flu. Sometimes, allergies produce severe respiratory symptoms as well. Symptoms of certain complications of the flu, such as pneumonia, produce similar symptoms.

This list focuses on conditions that may cause some or many of the same symptoms as the flu. Doctors sometimes use the term "flu-like" illness to describe an illness that has a similar clinical picture as the flu, but is not due to influenza virus infection. Not all of the conditions listed will cause the characteristic picture of the flu, but all of these conditions can cause some of the same symptoms.

Health concern on your mind? Visit the Symptom Checker.

REFERENCE:

MedscapeReference.com. Influenza differential diagnosis.

Main Article on Flu

Influenza Influenza (flu) is a respiratory illness caused by a virus. Flu symptoms include fever, cough, sore throat, runny nose, headache,...learn more »
Terms related to Flu:
- Influenza A
- Influenza Symptoms
- Influenza B
- Influenza C
- H1N1 Flu
- Seasonal Flu Symptoms
- Seasonal Influenza Symptoms

Causes of Flu

Allergy An allergy refers to a misguided reaction by our immune system in response to bodily contact with certain foreign substances. ...learn more »
In This Article
Allergy Article
- Allergy facts
- What does an allergy mean?
- What causes allergies?
- Who is at risk and why?
- What are common allergic conditions, and what are allergy symptoms and signs?
- Hay Fever
- Asthma
- Allergic Eyes
- Allergic Eczema
- Hives
- Allergic Shock
- Where are allergens? Everywhere
- In the air we breathe
- In what we ingest
- Touching our skin
- Injected into our body
ARDS (Acute Respiratory Distress Syndrome) Acute respiratory distress syndrome (ARDS) is a lung condition in which trauma to the lungs leads to inflammation of the lungs,...learn more »
In This Article
ARDS (Acute Respiratory Distress Syndrome) Article
- ARDS facts*
- What is ARDS?
- ARDS overview
- What are other names for ARDS?
- What causes ARDS?
- Who is at risk for ARDS?
- What are the signs and symptoms of ARDS?
- How is ARDS diagnosed?
- How is ARDS treated?
- What is the prognoisis of ARDS?
Bird Flu Bird flu (avian flu, avian influenza) infection in humans may result from contact with infected poultry. There is a vaccine to...learn more »
In This Article
Bird Flu Article
- Bird flu facts
- What is bird flu?
- What causes bird flu?
- What are risk factors for bird flu?
- What are bird flu symptoms and signs?
- How is bird flu diagnosed?
- What is the treatment for bird flu?
- What are the complications of bird flu?
- What is the prognosis of bird flu?
- Can bird flu be prevented with a vaccine?
- Where can people find more information about bird flu?
Chronic Obstructive Pulmonary Disease COPD (chronic obstructive pulmonary disease) is a disorder that persistently obstructs bronchial airflow. COPD mainly involves...learn more »
In This Article
Chronic Obstructive Pulmonary Disease Article
- Chronic obstructive pulmonary disease facts
- What is COPD?
- How does the normal lung work?
- What is chronic bronchitis?
- What is emphysema?
- What is chronic asthma?
- What is bronchiectasis?
- What causes COPD?
- What are the symptoms of COPD?
- How is COPD diagnosed?
- What treatment is available for COPD?
- Quitting cigarette smoking
- COPD Medications
- Bronchodilators
- Beta-agonists
- Anti-cholinergic agents
- Methylxanthines
- Corticosteroids
- Breo Ellipta
- Treatment of Alpha-1 antitrypsin deficiency
- What is the role of oxygen as therapy in COPD?
- What else is available for treating COPD?
- Future directions in COPD
Common Cold The common cold (viral upper respiratory tract infection) is a contagious illness that may be caused by various viruses. Symptoms...learn more »
In This Article
Common Cold Article
- What is the common cold, and what causes it?
- How is the common cold transmitted?
- What are the symptoms and signs of the common cold in adults, children, and infants?
- Does it have anything to do with exposure to cold weather?
- What is the difference between the common cold and influenza (the flu)?
- How is the common cold diagnosed?
- What is the treatment for the common cold? Are there any home remedies for the common cold?
- Are antibiotics a suitable treatment for the common cold?
- When should a physician or other health-care practitioner be consulted?
- How do you prevent the common cold?
- Common Cold At A Glance
Congenital Heart Defects Congenital heart defects are heart problems that are present at birth. Genetics may play a role in some heart defects. Symptoms...learn more »
In This Article
Congenital Heart Defects Article
- What are congenital heart defects?
- How the heart works
- What are the types of congenital heart defects?
- What are other names for congenital heart defects?
- What causes congenital heart defects?
- What are the signs and symptoms and signs of congenital heart defects?
- How are congential heart defects diagnosed??
- How are congenital heart defects treated?
- Living with a congenital heart defect
- Congenital Heart Disease At A Glance
Dengue Fever Dengue fever is contracted from the bite of a striped Aedes aegypti mosquito. Symptoms of dengue include headache, fever,...learn more »
In This Article
Dengue Fever Article
- Dengue fever facts
- What is dengue fever?
- What geographic areas are at high risk for contracting dengue fever?
- How is dengue fever contracted?
- What are dengue fever symptoms and signs?
- How is dengue fever diagnosed?
- What is the treatment for dengue fever?
- What is the prognosis for typical dengue fever?
- What is dengue hemorrhagic fever?
- How can dengue fever be prevented?
- Where can people get more information on dengue fever?
Hantavirus Hantavirus pulmonary syndrome (HPS) is a disease transmitted by rodents. Symptoms include fever and muscle pain. HPS can be...learn more »
In This Article
Hantavirus Article
- Hantavirus pulmonary syndrome (HPS) facts
- What is hantavirus?
- What is hantavirus pulmonary syndrome (HPS), and what are hantavirus pulmonary syndrome symptoms and signs?
- What is the history of hantavirus pulmonary syndrome?
- What causes hantavirus pulmonary syndrome?
- How is hantavirus pulmonary syndrome diagnosed?
- What is the treatment for hantavirus pulmonary syndrome?
- What are risk factors for hantavirus pulmonary syndrome?
- What are complications of hantavirus pulmonary syndrome?
- What is the prognosis of hantavirus pulmonary syndrome?
- Can hantavirus pulmonary syndrome be prevented?
- Where can people get more information on hantavirus pulmonary syndrome?
Human Immunodeficiency Virus HIV (human immunodeficiency virus) is the cause of AIDS (acquired immunodeficiency syndrome). HIV is a type of virus called a...learn more »
In This Article
Human Immunodeficiency Virus Article
- HIV facts
- What is the history of HIV, and when was HIV discovered?
- What tests are used in the diagnosis of HIV?
- How is HIV transmitted (spread)?
- What happens after an exposure to the blood or genital secretions of an HIV-infected person?
- What are HIV symptoms and signs in men, women, and children?
- What laboratory tests are used to monitor HIV-infected people?
- What are the key principles in managing HIV infection?
- Should patients with the flu- or mono-like illness of primary HIV infection be treated?
- What about treatment for HIV during pregnancy?
- What can be done for people who have severe immunosuppression?
- What is the future for HIV-infected individuals with regards to treatment simplification and cure research?
- What is in the future for preventing HIV transmission?
Infectious Mononucleosis Infectious mononucleosis is a virus infection in which there is an increase of white blood cells that are mononuclear (with a...learn more »
In This Article
Infectious Mononucleosis Article
- Infectious mononucleosis (mono) facts
- What is infectious mononucleosis?
- What is the cause of mono?
- What are risk factors for mono?
- How is mono transmitted or spread?
- What are the symptoms of mono?
- What are the signs of mono?
- How is mono diagnosed?
- What is the usual course and treatment of mono?
- What are the complications of mono?
- How can mono be prevented?
- Conclusion
Legionnaires' Disease Legionellosis is an infection caused by the Legionella pneumophila bacterium. There are two forms of legionellosis: Pontiac fever...learn more »
In This Article
Legionnaires' Disease Article
- Legionnaires' disease and Pontiac fever (legionellosis) facts
- What causes legionellosis? What is the history of Legionnaires' disease?
- How common is Legionnaires' disease?
- What are the usual symptoms of Legionnaires' disease?
- How is the diagnosis of Legionnaires' disease made?
- Who develops Legionnaires' disease?
- What is the treatment for Legionnaires' disease?
- How is Legionnaires' disease spread?
- Where is the Legionella bacterium found?
- How can Legionnaires' disease be prevented?
Lyme Disease Lyme disease is a bacterial illness, which is spread by ticks when they bite the skin. Initially the disease affects the skin...learn more »
In This Article
Lyme Disease Article
- Lyme disease facts
- What is Lyme disease? What causes Lyme disease?
- What is the history of Lyme disease?
- What are symptoms and signs of Lyme disease?
- How is Lyme disease diagnosed?
- What is the treatment for Lyme disease, and what is its prognosis?
- How can Lyme disease be prevented? Is there a vaccine?
Measles Measles (rubeola) is a highly contagious disease that's caused by a virus. Symptoms include a rash, high fever, cough, runny...learn more »
In This Article
Measles Article
- Measles facts
- What is measles?
- What is rubeola?
- What is rubella?
- What are other names for measles?
- What is the history of measles?
- What causes measles?
- How is measles spread?
- How does one become immune to measles?
- Who is at risk for getting measles?
- Is measles deadly?
- What is the danger of getting measles while pregnant?
- If I am exposed, how long does it take to develop symptoms and signs?
- What are measles symptoms and signs?
- What are the complications seen with measles?
- What is atypical measles?
- What is modified measles?
- How is the diagnosis of measles made?
- If it is not measles, what else could it be?
- What should I do if I have been exposed to measles?
- Is there any treatment for measles after symptoms and signs develop?
- If measles only rarely occurs in the United States, why should I get vaccinated?
- Do I need to be revaccinated against measles if I am traveling to Europe?
- What is the prognosis for measles?
- How can I prevent contracting measles?
- Is there any truth to the fear of getting autism from vaccines?
- Who should not receive measles vaccinations?
- If a child has an egg allergy, can they still receive the measles vaccine?
- What adverse reactions can occur to the measles vaccination?
- Who should be revaccinated against measles?
- Where can I find more information about measles?
Meningitis Encephalitis is a brain inflammation that causes sudden fever, vomiting, headache, light sensitivity, stiff neck and back,...learn more »
In This Article
Meningitis Article
- Encephalitis and meningitis facts
- What is encephalitis?
- What causes encephalitis?
- What are encephalitis symptoms and signs?
- What is meningitis?
- What causes meningitis?
- What are meningitis symptoms and signs?
- What is encephalomyelitis?
- How are encephalitis and meningitis diagnosed?
- What is the treatment of encephalitis and meningitis?
- What is the prognosis (outlook) for patients with encephalitis or meningitis?
- Is meningitis contagious?
- Can meningitis be prevented?
Migraine Migraine is usually periodic attacks of headaches on one or both sides of the head. These may be accompanied by nausea, vomiting,...learn more »
In This Article
Migraine Article
- What is a migraine headache?
- What are the symptoms of migraine headaches?
- What are some of the variants of migraine headaches?
- How is a migraine headache diagnosed?
- How are migraine headaches treated?
- What is the treatment for moderate to severe migraine headaches?
- What other medications are used for treating migraine headaches?
- How are migraine headaches prevented?
- What are migraine triggers?
- What should migraine sufferers do?
- What are prophylactic medications for migraine headaches?
- What is the proper way to use preventive medications?
- What is the treatment for menstrual migraine?
- Conclusions
Pneumonia Pneumonia is inflammation of one or both lungs with consolidation. Pneumonia is frequently but not always due to infection. The...learn more »
In This Article
Pneumonia Article
- Pneumonia facts
- What is pneumonia?
- How do people "catch pneumonia"?
- What are pneumonia symptoms and signs in adults and children?
- How is pneumonia diagnosed?
- What are some of the organisms that cause pneumonia? What is the treatment for pneumonia? Can pneumonia be prevented?
- What is the prognosis of pneumonia?
Rocky Mountain Spotted Fever Rocky Mountain spotted fever (RMSF) is an infectious disease that's transmitted by the bite of a tick infected with the...learn more »
In This Article
Rocky Mountain Spotted Fever Article
- Rocky Mountain spotted fever (RMSF) facts
- What is Rocky Mountain spotted fever?
- Where do most cases of RMSF occur in the U.S.?
- What is the history of Rocky Mountain spotted fever?
- What causes Rocky Mountain spotted fever?
- What are risk factors for Rocky Mountain spotted fever?
- What are symptoms and signs of Rocky Mountain spotted fever in children and adults?
- How is Rocky Mountain spotted fever diagnosed?
- What is the treatment for Rocky Mountain spotted fever in children and adults?
- What are complications of Rocky Mountain spotted fever?
- What is the prognosis of Rocky Mountain spotted fever in children and adults?
- How can people safely remove a tick?
- Can Rocky Mountain spotted fever be prevented?
- Where can people find more information on Rocky Mountain spotted fever?
Sinus Infection Sinus infection (sinusitis) signs and symptoms include headache, fever, and facial tenderness, pressure, or pain. Treatments of...learn more »
In This Article
Sinus Infection Article
- Sinus infection facts
- What is a sinus?
- What is a sinus infection?
- What causes sinus infections?
- What are the types of sinusitis?
- What are the signs and symptoms of sinus infection?
- How is sinus infection diagnosed?
- How is sinus infection treated?
- Are there home remedies for a sinus infection?
- What are complications of sinus infection?
- Can sinus infection be prevented?
- Related sinus infection article:
  Sinus infection - on eMedicineHealth
Swine Flu Novel H1N1 influenza A virus infection (swine flu) is an infection that generally is transferred from an infected pig to a human,...learn more »
In This Article
Swine Flu Article
- Swine flu (H1N1 influenza virus) facts
- What is the swine flu (novel H1N1 influenza A swine flu)?
- What causes swine flu (H1N1)?
- Why is swine flu (H1N1) now infecting humans?
- What are the symptoms of swine flu (H1N1)?
- How is swine flu (H1N1) diagnosed?
- What is the treatment for swine flu (H1N1)?
- What is the history of swine flu (H1N1)?
- What are the risk factors for swine flu (H1N1)?
- Can novel H1N1 swine flu be prevented with a vaccine?
- Can H1N1 be prevented if the H1N1 flu vaccine (or other flu strain vaccine) is not readily available?
- Is swine flu (H1N1) a cause of an epidemic or pandemic in the 2009-2010 flu season?
- What is the prognosis (outlook) and complications for patients who get swine flu (H1N1)?
- Where can I find more information about swine flu (H1N1)?