Because bed bugs can move between units without going outside. CDC and EPA state it plainly: "control in multi-family homes is much more difficult than in single family homes because bed bugs frequently travel between units, either by direct transport by humans or through voids in the walls." Treating one unit while an adjacent one stays infested is a documented reason infestations persist in this setting.
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Does that mean my whole building needs treatment at once?
The sourced guidance points toward coordination, though it doesn't specify a required scope. What is sourced is the mechanism: shared wall voids and human movement between units both let bed bugs re-enter a treated apartment from an untreated one nearby, which is worth raising directly with a building manager or property owner if you're coordinating treatment.
Where in a shared building do bed bugs concentrate?
The same places as anywhere else — about 85% in or near the bed, the rest in nearby upholstered furniture, cabinets, baseboards, and carpets. In a multi-family setting, add shared or adjacent walls to that list as a plausible entry point, and consider that a neighboring unit's infestation may be the actual source even if your own inspection turns up little near the exterior of the apartment.

Are shelters, dorms, and similar shared housing the same issue?
Federal guidance lists apartments, shelters, rooming houses, hotels, nursing homes, hospitals, and dorm rooms together as settings where infestations occur — the shared characteristic across all of them is population density and turnover, which increases the chances of an infested item or person introducing bed bugs to a shared space.
Sources
3 cited- Multi-family transmission mechanism: CDC & EPA, Joint Statement on Bed Bug Control in the United States, 2010 (checked 2026-08-18).
- Where bed bugs concentrate: UC IPM Pest Notes Publication 7454, Bed Bugs, May 2013 (checked 2026-08-18).
- Shared-housing settings list: CDC & EPA Joint Statement, 2010; UC IPM Pest Notes 7454 (checked 2026-08-18).
