Asked by user in New York.
In New York, landlords can be held liable for dangerous conditions. To establish liability in this specific case, you would need to prove that:
The biggest challenge you’re likely to face is proving that you contracted COVID-19 from the tenant. This will be challenging because your landlord can argue that you contracted COVID-19 from a visitor, or a tenant who the landlord didn’t know had COVID-19, or from some other person while you were outside the apartment. Generally speaking, it’s very difficult to prove exactly how you contracted COVID-19.
In the meantime, the Office of Civil Justice offers free legal help for residents in New York who are having problems with their landlords. You can find more information here.