We recently moved into an older home (although the plumbing is quite new) and have noticed that when we don't use the bathroom shower, or guest toilet or kitchen sink for a bit (i.e. leave home for a few days) we return to a foul stench coming from these sources. It seems to go away once we start to reuse again (i.e. the drains get flushed out).

What causes this and is there anything that can be done to remedy?

Most bad smells in tubs, lavatorys and showers are caused by rotting hair matted with grease from the soap. Try this for the smell. Tonight before bedtine Take a 1/2 gallon of bleach and pour it down the drain and let set over night. Next morning ,(and this is important) flush out the drain with two large pans of boiling water to loosen the grease and flush the mess out. The bleach will make the hair slippery and began to dissolve it and the hot water will melt the grease and flush the mess away.
Also, pull the lavatory stopper and look down the drain. About 4 inches down you'll see a small rod sticking out. Fish out any hair that's caught there and do the same thing to the lavatory if you detect any odor. The kitchen sink has garbage built up on the pipe walls that can smell. Do the bleach thingey there also. Also if you have a disposal cut a lemmon into four pieces and run them through for a better smell. This should make your drains smell better. Good luck, Tom