DefinitionA small purplish spot on a body surface, such as the skin or a
mucous membrane, caused by a minute
hemorrhage of underlying capillaries and is often seen in
typhus.
Serious condition
In typhus the characteristic red rash can become petechial/hemorraghic and necrotic. The necrosis (dead tissue) can be the source of gangrene, which if not controlled will lead to the death of the infected person.
Other uses of the term
In the field of criminology and forensics, the term petechia is also encountered. It usually denotes minute hemorrages caused by strangulation or bindings. The term is used to describe the intradermal bleeding caused by the aforementioned violence.
Caution is the best policy
The presence of petechial spots on adult persons can be a telltale sign of a long list of ailments. The person who exhibits these spots should seek medical attention to identify the causative agent. The list of possible causes can vary from leukemia to ebola, therefore caution dictates seeking appropriate medical care.
A matter of degree
.
Petechia are different than bruises in that they are usually smaller while bruises are generally larger. The usual causes of bruising are injuries such as being struck, falls, and other common accidents. There are other causes for bruising such as a plethora of diseases, so the cautions given above certainly apply.
Sources:
http://www.answers.com/topic/petechia
http://en.wikipedia.org/wiki/Petechia