Flu affects millions of Americans each year, according to the Centers for Disease Control and Prevention, or CDC. Less is known about the incidence of colds because fewer people report them, but it is generally accepted that they occur more often than the flu, hence the name "common cold." Since both are respiratory viruses, they produce similar symptoms. There are subtle differences, but the only way to confirm the diagnosis one way or another, says the CDC, is through laboratory tests.
Fever
According to the American Academy of Family Physicians, both flu and colds can be accompanied by fever. In the case of flu, fever usually exceeds 102 degrees F, while fever due to cold is usually low-grade or even subjective, where the patient feels feverish, although temperature technically measures normal.
Respiratory Symptoms
With flu, lower respiratory symptoms such as dry cough, chest pain and tightness and mild breathing problems predominate. With colds, upper respiratory symptoms such as runny nose, nasal congestion and sore throat due to post-nasal drip predominate. In the case of flu, upper respiratory symptoms sometimes do appear a day or two after lower respiratory symptoms, especially in children, but, according to "Harrison's Principles of Internal Medicine," lower respiratory symptoms never accompany a cold.
Pain
Pain symptoms figure prominently into both flu and colds. Flu is characterized by headaches in the front part of the head or all over, sore muscles in the back and legs, and sensitivity or burning in the eyes. Colds usually produce sinus headache, sore throat due to post-nasal drip and tender skin below the nose due to irritation from mucus and abrasion by tissues.
Gastrointestinal Symptoms
People with flu and colds rarely report much appetite. In the cases of flu, about 40 percent of people also experience vomiting, diarrhea or both, according to a 2009 study in the "New England Journal of Medicine."
Onset
Another key difference between flu and colds lies in the presentation of symptoms. With flu, says Harvard Medical School professor Raphael Dolin, symptoms start suddenly, so suddenly that many patients can describe the exact time when they became ill. With colds, patients often describe tingling in the nose, increased need for sleep, or an overall sense that they were getting sick a few days before symptoms actually appear.
Seasonality
According to the American Academy of Family Physicians, over 200 different viruses produce the symptoms people ascribe to the "common cold," so colds exhibit no seasonality. Flu season, on the other hand, runs from November to May in the United States and other Northern hemisphere countries. Southern hemisphere countries follow the opposite pattern.
References
- "Harrison's Principles of Internal Medicine;" A.S. Fauci et al. (eds.); 2008
- American Academy of Family Physicians:
- "New England Journal of Medicine;" Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans; Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team; June 18 2009
- Centers for Disease Control and Prevention: Cold Versus Flu?
- Centers for Disease Control and Prevention: The Flu Season
