An infection is an illness caused by microorganisms or bacteria that invade the body. The body's defenses against infections begin with blocking the entry of microorganisms into the system. Hand washing is an effective strategy in preventing the entry of microorganisms into the body through the skin, the respiratory system, or the GI (gastrointestinal) tract.
Local infections may produce redness, tenderness, and swelling, but systemic infections produce more serious symptoms such as fever, chills, sweats, and fatigue. Many infections will go away on their own, however, as the body's immune system can successfully fight off many infections. Others, however, require treatment, such as the use of antibiotic medications.
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![Glandular fever, or mononucleosis, is a viral infection that causes inflamed tonsils (shown here) and fever, and may cause an enlarged spleen. Symptoms most often appear in teens, but more than 80 percent of adults in the United States carry the virus and can transmit it. [Science Photo Library/Photo Researchers, Inc. Reproduced by permission.]](/images/gale/thumb/nwaz_02_img0137_thumb.jpg)