[pdftex] Getting the correct word spacing after Macros.

[Michael Chapman]

Apologies in advance, this is more Latex than pdfLatex, but I have difficulty 
finding keywords to search the archives for what must(?) be a trivial 
question.

I have a document with several dozen complicated words/phrases. To 
trivialise, if I were to set:

\newcommand{\USA}{United States of America}

is there an easy way of making the command so a space is (automatically) 
inserted if the next character is a letter or number, but no space is 
inserted if the next character is punctuation.
(E.gg. 	It happened in United States of America. 
	In the United States of America it is common for people ....)

Have thought of a regular expression search of the file and/or trying to get 
into if/then programming of Latex, but I feel I must be re-inventing the 
wheel ... !

Thanks for any advice (even if I do blush!),

		Michael.