Flu Influenza Symptoms

Symptoms of the flu can vary from mild to severe—and in some rare cases, the flu is fatal. Because the flu result in serious health complications—particularly for those with weakened immune systems—it’s important to learn to recognize common flu symptoms. Identifying the symptoms of the flu early is particularly important to maintain the health of young children, older adults and those with weak immune systems.

Not all influenza viruses that cause the flu are created equal. The three different types of human influenza are labeled A, B, and C. Viruses of the influenza A type are the most worrisome, as they are the ones that cause much suffering each flu season. The viruses of the influenza B and C type are of less concern, as they are less common and cause milder symptoms.

The H1N1 virus, also known as the “swine flu,” belongs to the influenza type A category. The H1N1 virus is known to cause very severe symptoms in some people. According to the World Health Organization, as of December 2009, it was responsible for more than 8,000 deaths worldwide.

Seasonal Influenza - Symptons of Seasonal Influenza

Influenza Type A Symptoms

In humans, influenza Type A causes moderate to severe symptoms, such as:

  • Body aches
  • Chills
  • Couging
  • Fatigue
  • ever
  • Sniffling and sneezing.

Several different methods are used to measure body temperature. The most accurate way involves a rectal measurement, but the preferred method is oral (under the tongue). There is really no set “normal” temperature, but a fever is generally regarded as over 100.4 degrees Fahrenheit. Fever serves as one of the body’s natural defenses against foreign microorganisms, which usually cannot live at a higher temperature. It also allows your body’s defense mechanisms to work more efficiently.

Other, less common symptoms of the flu include:

  • Dizziness
  • Flushed face
  • Headache
  • Nausea
  • Vomiting.

The flu actually has phases. Sometime between the second and fourth day of the flu, the severity of the above symptoms usually begin to decrease, and respiratory symptoms begin to increase.

A dry, hacking cough is usually the most prominent (and most annoying!) of the respiratory symptoms. Most people also develop a sore throat, headache, runny nose, and sneezing. These symptoms (except the persistent cough) usually disappear within four to seven days.

Other symptoms may include:

  • Loss of appetite
  • Muscle aches and stiffness
  • Stuffy, congested nose
  • Sweating
  • Worsening of underlying illness, such as asthma or heart failure.

Swine Flu Symptoms

Symptoms of swine flu are similar to influenza type A symptoms. Fatigue is reported in nearly all cases, and those infected may also experience nausea, vomiting, and diarrhea. The worse symptoms involve the respiratory system and some may need hospitalization and artificial respiratory support. Death can occur from secondary bacterial infections of the lung on top of the viral infection. What is peculiar about the swine flu is that it is affecting many young, healthy adults.

Because the symptoms of swine flu are so similar to regular seasonal flu, the diagnosis is usually made clinically with thorough review of patient history. A definitive diagnosis of swine flu requires collecting a swab sample from within the first four or five days of illness and sending the sample to the Centers for Disease Control for laboratory testing.


Centers for Disease Control and Prevention staff. (2009). Seasonal influenza (flu): Key facts about swine influenza (swine flu). Retrieved November 30, 2009, from the CDC Web site: http://www.cdc.gov/flu/swineflu/key_facts.htm.

CNN staff. (n.d.). H1N1/Bacterial pneumonia. Retrieved November 30, 2009, from the CNN Web site: http://www.cnn.com/2009/HEALTH/11/26/h1n1.bacterial.pnuemonia/index.html.

Medline Plus staff. (2009). Flu. Retrieved November 30, 2009, from the National Institutes of Health Web site: http://www.nlm.nih.gov/medlineplus/ency/article/000080.htm.