The original article (PDF) on which all the news stories were based is naturally a little less thrilling and a lot more factual, and is interesting from an etymological point of view, as well as an entomological one. (I'll pause to allow readers to check that I have these the right way around.)
The article refers to
pest control companies ... experiencing a true worldwide bed bug pandemic.(My italics.)
Compare this to the paraphrasing in all the news articles:
Australia is suffering a bed-bug epidemic ... The Australian outbreaks are part of a global epidemic(My italics again.)
I can see three possible reasons for this word substitution:
1. The journalists think epidemic and pandemic are synonyms.
2. The journalists had never heard of pandemic and assumed the scientist made a mistake in his article.
3. The journalists thought that their readers would not understand what a pandemic was, or would not be sufficiently alarmed, so they chose a more recognisable and presumably scary word.
In fact the reverse is true, and, not surprisingly, the scientist was using the terms correctly, because a pandemic indicates that both the area involved and the population affected is much larger that in an epidemic. As WiseGeek helpfully puts it,
... epidemics that grow out of hand due to the nature of the disease and other factors, turn into pandemics.
As a footnote, an amusingly parochial interpretation of the term "pandemic" can be found in "The Arizona Republic", which proudly reported that
... the bugs are returning to beds throughout the country, including in Arizona.