This is going to be a short post- but I just wanted to put down a thought I had after watching the movie 'Andromeda Strain' a couple nights ago. That movie stressed how dangerous that contact with 'extra terrestrial' germs could be. And when you look at history- like the Spanish exploration/conquest of the "new world", it is easy to see what a huge effect introducing new germs into a previously isolated ecosystem would have.
In the Galaxy spanning setting of Star Wars, I can only imagine what a nightmare disease would be- when you have people living among all manner of different species- to say nothing of the exploration of previously undiscovered worlds. While the 'civilized' galaxy might have sorted out its disease problems over the centuries, one would think that contact with new worlds would constantly introduce new threats.
However, we do not see disease running rampant in any Star Wars stories that I know about—save for a few relatively isolated instances (like where Vader destroys a Faleen city to stop the spread of a particular plague). Now I know that this was probably done for the sake of cinema. Nobody wants to watch an adventure story about people visiting a new world, contracting horrible diseases, and dieing. Even so, I like to have some kind of 'in-character' explanation for these things- without getting TOO 'scientific' about it.
The explanation I came up with is this:
Medical science in the Star Wars galaxy- specifically the science of disease control- has reached a VERY advanced level. The majority of the galaxy's population has been 'immunized' with advanced (species specific) serums, thus giving them protection versus almost all known diseases and most 'new' ones as well. However scientifically implausible this may be, it is a nice, simple explanation as to why there aren't constant epidemics with every visit to a new world.
Of course, this still leaves room for health problems- what if a 'super disease' could overcome standard immunization techniques. And there is still the problem of newly discovered and/or isolated species contracting diseases FROM the 'civilized' galaxy. In this way, you can still include diseases as a threat in your campaign without making them the main focus.
Works for me anyway.