How many people are susceptible to have osteomyelitis?

Hard to answer. People with normal immune systems are not generally susceptible to osteomyelitis. Osteomyelitis is not a frequent disease, but there are certain factors that contribute to developing it. Bloodstream infection, called sepsis, is a major one. Also, traumatic injuries causing exposure of the bone to the outside environment may lead to it. Weakened immune system also predisposes to it.
People. With DM, peripheral vascular disease, smokers, history fracture with skin break, history of foreign bodies and history immune deficiency and smoking.
Everyone. Osteomyelitis is an infection with in the bone. Some people are more susceptible but anyone with an infection can get it in the bone and that's osteomyelitis.