Infection is a term used to describe the invasion of a host organism by a pathogen, such as a VIRUS, bacteria, or fungus. An EPIDEMIC is a widespread occurrence of an infectious DISEASE in a community at a particular time. IMPURITY is the presence of unwanted substances in something that should be pure. ILLNESS is a state of poor health caused by an infection or other medical condition. MIASMA is a noxious atmosphere or vapor believed to cause DISEASE. CONTAMINATION is the process of making something impure by contact with or addition of a poisonous or polluting substance. CONTAGION is the transmission of a DISEASE from one person or organism to another. POLLUTION is the CONTAMINATION of the environment by harmful substances. AILMENT is a minor ILLNESS or physical disorder. DISEASE is a disorder of structure or function in a human, animal, or plant, especially one that produces specific symptoms or that affects a specific location and is not simply a direct result of physical injury. TAINT is a trace of something bad or unpleasant that spoils or contaminates something else. VIRUS is a small infectious agent that replicates only inside the living cells of an organism. Staph is a type of bacteria that can cause a range of illnesses from minor skin infections to life-threatening diseases.