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I don't think, that's cheap, as it would require  good amount of AI programming

Ahh ok,  true im a no good at programing.

Than simpler version of disease.

Space flu outbreak - colonists get slight penalty (to morale/tasks)  and some coughing noises sound and that's it. Also it would pass after few days, variying for each colonist.

More could be added...

Huh, so cheap stuff?

Apart from adding variety, i would like to add concept of various diseases.

in order of difficulty:

space flu - spreads quickly, mildly irritating, passes on its own

Coughing disease - nasty, spreads, needs doctoring

Red swelling - puts colonist to the bed, does not spread, need doctoring to pass

Gut rot - This one can kill colonist, does not spread, needs research to cure.

Ok, these are just basic ideas, it could easily be added several more variations.

Hope it helps