From Latin ec- (a variant of 'ex' found in prefixes, meaning 'out' or 'out of') and Greek -demic (in the same way as epidemic) from 'δεμος' meaning 'people'.
The virtual antonym to endemic, 'ecdemic', as a noun, describes a disease which is brought into an area from without.
An good example of an ecdemic disease would be the Black Plague of the 14th century, brought into countries by rats on trade ships. Contrast this with a disease like malaria, which is endemic to sub-Saharan Africa.
The word 'ecdemic', like its antonym, has been extended for use in non-specialist conversation as an adjective for anything that is brought in from outside. For example, 'It widely introduces all kinds of ecdemic talents.' (Ningbo Today.) Despite this use, it still remains a fairly obscure word.
See also:
Sources:
A.Word.A.Day
http://phrontistery.50megs.com/e.html
http://www.paul_smith.doctors.org.uk/Epidemics.htm
http://www.dictionary.com/