Final answer:
Osteomyelitis is the most common deep infection in pediatrics. It is predominantly caused by Staphylococcus aureus, and though other bacteria like Streptococcus agalactiae can cause it, Haemophilus influenzae is more commonly associated with meningitis.
Step-by-step explanation:
The most common deep infection in pediatrics, especially in adolescents and young adults, is osteomyelitis.
Osteomyelitis is an inflammation of bone tissues, which is most commonly caused by infection. The primary bacteria responsible for osteomyelitis is Staphylococcus aureus. This condition can manifest either as acute or chronic and involves different bacteria depending on the bones affected. In children, bacteria usually enter the bloodstream and spread from focal infections, often affecting the long bones such as the femur. In adults, direct access to the bone tissues through trauma or surgical procedures, including those involving prosthetic joints, are common ways for bacteria to cause infection.
Among other bacteria which can cause osteomyelitis are Streptococcus agalactiae and other Enterobacteriaceae species. It’s important to note that the bacterium Haemophilus influenzae is known for causing types of infections such as meningitis, especially in children before the widespread use of the Hib vaccine, but it is not the most common cause of osteomyelitis.