Troublesome/Revolting Tenant Advice

[William Conrad]

Last year I purchased a four-unit multi-family with 50% occupancy. Before purchase, I noticed cat feces on the floor of one of the occupied apartments. It was concerning, but not a reason not to buy. I assumed, perhaps incorrectly, that it was an anomaly. Well, workers recently entered the apartment and refused to do work because...you guessed it--cat feces on the floor. Even worse, the tenant had a baby recently so now not only is my building at risk, so is a child. What should i do? I can't just walk in an continually investigate. Upon renewal do I say pets aren't allowed? She's a (fairly) reliable tenant, but this clearly is unacceptable on many, many levels. Ideas?