you probably want to talk to a lawyer.

there are two different things. One is a person has a medical condition that results in his disability that he can not pay or he can not live there (e.g, can't climb stairs). In general only elderly tenants (age 62 and above) can claim this reason and give 30 days notice without the obligation to finish the lease.

the other is that the cause of the tenant's illness comes from the house. In this case the tenant may be entitled for  some compensation from the landlord, or can ask the landlord to make remedies to remove the cause. Generally if a genuine cause can be established, the tenant does not have to pay rent until such remedies is completed.