Sorry to hear. I have never had experience with Brook but I do believe it is clownfish specific. Not 100% sure though.
Another guy on here, djam, recently lost 2 clowns as well but he doesn't know what caused the death. I was suspecting Brook as the culprit myself. Sounds like it may be going around.
Edit: pgr11 is right. Brook does kill FAST. What have you added new in the last couple weeks?