How fast will osteomyelitis spread?

Few days if : No trearment given.

Depends on organism: Some bacteria are less aggressive than others. In todays world methicillin resistant staphylococcus (MRSA) is very aggressive and can destroy bone in days. MRSA can involve entire bones and multiple bones in body. If not treated successfully complications include loss of bone integrity, fracture, recurrent osteomyelitis, and septic emboli to lungs. Septic thrombophlebitis, myositis, and abscesses.

Varies: It varies for each individual, based on other medical conditions the patient may or may not have.