A screening is just what they call the tests they will do. It might be because of your work, although I work in the NHS and haven't had this, it'll be different in every area likely. I wouldn't worry too much. MRSA is usually identified in hospitals because people are tested there, and not usually tested at home. If they do find you have it and want to treat it, they will likely give you anti-biotics, or a local treatment depending on where they find it.