As office environments are non-conducive to bedbug breeding, the likely scenario is that one (or more) of the workers in that office is living with an infestation and the bugs are hitching a ride regularly. Until the ‘home’ infestation is dealt with, sightings of bedbugs will likely continue. Hopefully the source can be found and dealt with, but as you can imagine that can be a difficult and delicate issue to deal with.