A 10-year-old boy is brought to the emergency department after experiencing high fevers and chills for the last few days. He also complains of dull pain just above his left knee. He has no history of recent trauma other than minor scrapes to his knees and elbows while playing outside. Physical examination shows point tenderness 3 cm above the kneecap. There is no joint effusion. Radiographs show soft-tissue swelling and a periosteal reaction over the lower end of the femur. Which of the following organisms is most likely responsible for this patient's symptoms?

Question

A 10-year-old boy is brought to the emergency department after experiencing high fevers and chills for the last few days.  He also complains of dull pain just above his left knee.  He has no history of recent trauma other than minor scrapes to his knees and elbows while playing outside.  Physical examination shows point tenderness 3 cm above the kneecap.  There is no joint effusion.  Radiographs show soft-tissue swelling and a periosteal reaction over the lower end of the femur.  Which of the following organisms is most likely responsible for this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_38a5_6fc9_9249_f77e61f5840f_MD0001_00 Osteomyelitis is an infection of bone and bone marrow that occurs by 1 of 3 mechanisms: Hematogenous osteomyelitis occurs predominantly in children (particularly boys) and most frequently affects the long bones. The tibia, fibula, and femur are most often involved. Adults who develop the condition are more likely to have vertebral involvement and frequently have a predisposition to bacteremia due to risk factors such as IV drug abuse or indwelling vascular catheters. The presenting symptoms of hematogenous osteomyelitis are vague, and a high index of suspicion is required to make the diagnosis. Initial symptoms such as malaise and fevers are non-specific. As the infection progresses, infants and younger children may refuse to move the affected extremity. Older children often complain of pain over a long bone. Bone pain develops as the abscess expands within the bone, leading to bone necrosis, periosteal disruption, and swelling of the surrounding soft tissue. Staphylococcus aureus is implicated in most cases of acute hematogenous osteomyelitis in otherwise healthy children. (Choice A) Enterococcus faecalis causes a variety of infections, including endocarditis, meningitis, and urinary tract infections. Enterococcus can cause vertebral osteomyelitis after a recent urinary tract infection via bacteremic spread. (Choice B) Moraxella catarrhalis is a part of the normal flora of the upper respiratory tract. It causes otitis media and sinusitis in healthy individuals and is frequently responsible for causing exacerbation of chronic obstructive pulmonary disease. (Choice D) Staphylococcus epidermidis is ubiquitous in nature and is commonly isolated in cultures as a contaminant. However, S epidermidis can also be pathogenic, colonizing intravenous catheters and other foreign bodies such as prosthetic heart valves and orthopedic hardware, leading to bacteremia and sepsis. (Choice E) Streptococcus agalactiae (group B streptococcus) frequently colonizes the gastrointestinal and urogenital tracts. Infants born vaginally to colonized mothers can develop serious neonatal infections, including sepsis, pneumonia, and meningitis. For this reason, pregnant women testing positive for group B streptococci are treated with antibiotic prophylaxis during labor and delivery. (Choice F) Streptococcus pneumoniae is the most common etiologic agent of community-acquired pneumonia. It also causes otitis media in children, sinusitis, meningitis, and sepsis. (Choice G) After Staphylococcus aureus, Streptococcus pyogenes (group A streptococcus) is the second most common cause of hematogenous osteomyelitis in children. Group A streptococci are also responsible for streptococcal pharyngitis and skin infections such as impetigo and necrotizing fasciitis. Educational objective: Hematogenous osteomyelitis is predominantly a disease of children that most frequently affects the long bones. Staphylococcus aureus is implicated in most cases secondary to a bacteremic event. Streptococcus pyogenes (group A streptococcus) is the second most common cause of hematogenous osteomyelitis.

A 10-Year-Old Boy Is Brought to the Emergency Department After