Fleas in an apartment: Who's responsible?

[Nathan McBride]

I have a tenant in an upstairs unit that notified me that they have fleas in their apartment.  This is a two-story standalone building consisting of two efficiency apartments, one on top of the other.

The tenant below them does not have fleas, and neither do the tenants in the front house.

I bug bombed the apartment in question, and the tenant claims to have bombed it again.  But they said they still have fleas.

At this point, I feel like it is fairly safe to say that they brought the fleas in with them or at least their cleaning habits (or lack thereof) have contributed to the problem.

Anyway, my question is who is ultimately responsible in this case?  I've been trying to treat the place, but if they don't clean up after themselves, there's only so much I can do.  Fleas love hiding in piles of dirty laundry.

Treatment would be simple if they and their stuff were out of the apartment.

To prevent this problem in the future, I will be putting pest control on the tenant in my leases (but continuing to spray the outside).

Any advice would be greatly appreciated.

-Nathan