>CONTAINMENT SPECIALIST
>
>When you *enter* a city with 2 or more disease cubes of the same color, remove 1 of them.

Upon entering the city with two or more cubes of the same color, the Containment Specialist removes 1 of those cubes - that's it.

This ability has absolutely nothing to do with treating the disease.

In particular it doesn't care whether the disease is cured or not.