Pattern is the shape of the problem across the room. Uniform: every bag the same, usually environment or a whole compost or casing lot. Spreading: a few bags on day one, neighbours by day three, the signature of infection or a moving pest. Localised: only under the leak or by the door, so look for a physical cause there. Single bag: one odd bag, often a filling or spawn fault.
Speed matters as much as shape. ICAR-DMR warns that dry bubble, left uncontrolled, can destroy a crop in 2 to 3 weeks. A count that doubles every two days is an emergency; a flat count is a fault, not an epidemic.