Final answer:
Staphylococcus aureus, particularly MRSA, is the most common cause of osteomyelitis in IV drug users. These bacteria can enter the bloodstream through needle use and then infect the bones.
Step-by-step explanation:
The most common cause of osteomyelitis in IV drug users is the bacteria known as Staphylococcus aureus, with methicillin-resistant Staphylococcus aureus (MRSA) also being a notable pathogen due to its resistance to many standard antibiotics.
In IV drug users, infections can result from the introduction of bacteria directly into the bloodstream through needle use. Infected material can then be transported to the bone, resulting in osteomyelitis. It is critical that these infections are treated promptly to prevent complications such as sepsis and the potential need for surgical intervention.