@Tracey Thornton
I had/have a similar situation. I have owned my duplex for 10 years. None of my previous tenants ever complained about bed bugs.
In March a new tenant moved in upstairs. In August a new tenant moved in downstairs. Two weeks after the downstairs tenant moved in, the upstairs tenant said she has bed bugs.
I called a bed bug company and we did a walk through inspection of both apartments. The downstairs tenant said that she does not have a bed bug issue. When we did the inspection upstairs, the place was a pig stye. There were bags and bags of garbage piled up in the stairwell outside of the kitchen door. It stunk! She said that it was garbage from that week because garbage pickup is only once a week. This was way more than one week of garbage. She also has no furniture, except for beds. All of her clothes are in plastic bags throughout the apartment. The inspector did find evidence of bed bug by-product on the mattress but could not find any bed bugs, dead or alive. Th mattress was also full of all types of stains from who knows what. The inspector then advised her that if she saw "another" one, to either keep it to show him or take a picture of it. After he left, I told her that her apartment is unsanitary and the garbage has to be disposed of. She is young, maybe 28, but not that young that she does not know how nasty it is to keep all of that garbage piled up outside her kitchen door. I also took pictures of every room in the apartment to document the condition. Finally, i told her that I would give her one week to clean her apartment and remove the garbage. After that time, I would come back and do an inspection. If she still had bugs, I would call the inspector back.
So far, she has not mentioned anything else about bugs and I was there last week. The apartment was also a whole lot cleaner that it was before.
My lease does say that any pest or rodent problem identified within the first month of move in is the responsibility of the landlord. After a month, it is the responsibility of the tenant.