A 12-year-old boy with sickle cell disease is brought to the emergency department because of a 3-day history of fever and worsening pain in his left thigh. He refuses to bear weight on the leg. His mother notes that he had a “stomach flu" two weeks ago that resolved without treatment. His temperature is 39.2°C (102.6°F), and the rest of his vital signs are within normal limits. On physical examination, there is significant tenderness and warmth over the distal left femur, but the knee joint has a full range of motion without effusion. Laboratory studies show a leukocyte count of 18,000/mm3 and an erythrocyte sedimentation rate (ESR) of 85 mm/h. Plain radiographs of the femur are unremarkable.
Which of the following is the most likely causative organism?
The correct answer is:
C) Salmonella enteritidis
This patient has findings consistent with acute hematogenous osteomyelitis. While Staphylococcus aureus is the most common cause of osteomyelitis in the general pediatric population, patients with sickle cell disease have a uniquely high predisposition to Salmonella species. This is due to several factors, including functional asplenia (impaired clearance of encapsulated organisms) and microinfarctions in the gut mucosa that allow Salmonella to enter the bloodstream and seed the bone. The clinical presentation involves localized bone pain, fever, and elevated inflammatory markers. Note that the X-ray is often normal in the first 7–14 days of infection. MRI is the most sensitive imaging modality for early diagnosis.
Answer choice A: Kingella kingae, is incorrect. This is a common cause of osteomyelitis and septic arthritis in children under the age of 4, but it is not specifically associated with sickle cell disease.
Answer choice B: Pseudomonas aeruginosa, is incorrect. Pseudomonas aeruginosa is classically associated with osteomyelitis following a puncture wound through a sneaker, as the organism thrives in the moist environment of the foam padding.
Answer choice D: Staphylococcus aureus, is incorrect. In most children, this is the #1 cause of osteomyelitis. However, in the setting of sickle cell disease, Salmonella is either the most common or second-most common (depending on the study), but it is the classic board exam association you must prioritize for this specific patient population.
Answer choice E: Streptococcus pyogenes, is incorrect. Group A Strep can cause osteomyelitis and skin infections (cellulitis), but it is not the primary pathogen associated with the complications of sickle cell disease.
Key Learning Point
Acute osteomyelitis in children typically presents with fever and localized bone tenderness. In the general population, S. aureus is the most common pathogen. In patients with sickle cell disease, Salmonella and S. aureus are the leading causes. For boards, if a sickle cell patient has bone pain and fever, think Salmonella.
