The first task the exterminator faces is to discern the source of the bugs. I have found that, in cases where bugs are self reported, that it is the nice conscientious tenant that first reports the bugs. But if one starts looking around the original source of those bugs is elsewhere. And when I start inspecting suites I find that 80% or more tenants must be told they have bed bugs. It is in one of these suites that the infestation most likely originated. The suite with the heaviest infestation is likely the original source. As such it is important that the first person who complains is treated with great respect as he/she is likely one of your better tenants and is behaving in a responsible manner.
The most likely source of the bugs is from the suite beside, below, or above the tenant. All these suites must be, at minimum, carefully inspected. I would also inspect the suite across the hallway as bugs are sometimes found there as well.
The exterminator must then ask some questions regarding the mysterious appearance of mattresses and couches in the alley behind the apartment block. If there has been an increase in these items in recent months it is good for the landlord to put out feelers for where these items came from. Sometimes the answer is readily available – it is suite so and so. That suite must be inspected as the tenant may be attempting to self treat bed bugs and may have dropped a few bugs in the hallway or pushed them to other suites via aerosol pyrethrin (RAID, KONK, etc).
Another helpful question is to ask the infested tenant if they visit anyone in the building? All suites frequented by the infested person should be inspected. A secondary part of this query is ascertain if the tenant frequents, or his/her guests frequent, high risk areas such as rooming houses, public housing, homeless shelters, homes known to contain bed bugs, or perhaps works in a high risk environment such as a home care worker or social worker who attends many homes on a professional basis. If these risks are present the tenant must be educated on how to reduce those risks. If those risks are present and precautions are not taken a re infestation is imminent. Prevention is always superior to treatment.
If several suites are found to contain bed bugs with these searches, especially if they are in separate areas of the building, it is best to monitor the entire building.