A 7-year-old boy is brought to the emergency department due to fever and right leg pain. The patient's symptoms began 3 days ago, when his parents noticed him limping. He had mild right lower leg pain at that time, but subsequently developed fever, fatigue, and decreased appetite 2 days ago. The patient's pain is currently 7 on a scale of 0-10 in severity, is nonradiating, and is unrelieved by ibuprofen, heat, or rest. He has no history of trauma and is otherwise healthy. Immunizations are up to date. The patient's second cousin has sickle cell disease. Current temperature is 39.4 C (102.9 F), blood pressure is 100/70 mm Hg, pulse is 138/min, and respirations are 22/min. Examination of the right leg shows bony point tenderness, erythema, and warmth over the proximal tibia. Blood is drawn for culture. Which of the following organisms will most likely be isolated from this patient's blood?

Question

A 7-year-old boy is brought to the emergency department due to fever and right leg pain.  The patient's symptoms began 3 days ago, when his parents noticed him limping.  He had mild right lower leg pain at that time, but subsequently developed fever, fatigue, and decreased appetite 2 days ago.  The patient's pain is currently 7 on a scale of 0-10 in severity, is nonradiating, and is unrelieved by ibuprofen, heat, or rest.  He has no history of trauma and is otherwise healthy.  Immunizations are up to date.  The patient's second cousin has sickle cell disease.  Current temperature is 39.4 C (102.9 F), blood pressure is 100/70 mm Hg, pulse is 138/min, and respirations are 22/min.  Examination of the right leg shows bony point tenderness, erythema, and warmth over the proximal tibia.  Blood is drawn for culture.  Which of the following organisms will most likely be isolated from this patient's blood?

Quizplus · Accepted Answer

11ec25c8_d283_9c26_bc81_9fb2b1b7f104_MD0003_00 Osteomyelitis is a bone infection most commonly caused by Staphylococcus aureus. In children, the infection typically occurs when bacteria spread hematogenously and seed the richly vascularized metaphyses of long bones (eg, femur, tibia). Risk factors for osteomyelitis include sickle cell disease and immunodeficiency, but healthy children with no chronic medical problems can also develop osteomyelitis. spread hematogenously Presentation includes systemic symptoms (eg, fever, irritability) in addition to signs of localized bony inflammation, such as point tenderness and swelling. Patients often avoid using the affected limb, such as this patient with a limp. Initial evaluation includes laboratory studies (complete blood count, erythrocyte sedimentation rate, C-reactive protein), blood cultures, and x-rays of the affected area. MRI is typically performed to identify signs of infection as early x-rays are often normal. Patients are often diagnosed and treated presumptively based on clinical presentation, elevated inflammatory markers, and imaging findings. However, bone biopsy and/or culture is the gold standard for definitive diagnosis. Empiric treatment is with intravenous antistaphylococcal antibiotics; cultures from the blood or bone, if positive, help guide therapy. (Choices A and F) Escherichia coli and Streptococcus agalactiae (group B Streptococcus) are commonly implicated in neonatal osteomyelitis. This school-age child is more likely infected with S aureus. (Choice B) Pseudomonas aeruginosa is associated with osteomyelitis of the foot after a puncture wound of the plantar surface. Intravenous drug use also increases risk of P aeruginosa osteomyelitis. (Choice C) Because of their impaired splenic function, patients with sickle cell anemia are at increased risk of osteomyelitis caused by encapsulated organisms such as Salmonella species. Although he has a second cousin with sickle cell disease, this patient does not have any manifestations of the condition (eg, no history of vaso-occlusive crises). (Choice E) Staphylococcus epidermidis, a component of normal skin flora, is associated with infection in patients who have indwelling vascular (eg, hemodialysis) catheters. (Choice G) Streptococcus pyogenes (group A Streptococcus) commonly causes cellulitis and septic arthritis but is rarely implicated in osteomyelitis. Educational objective: Osteomyelitis is a bacterial infection of the bone that typically presents with fever and focal bony pain. Infection is most often caused by hematogenous spread of Staphylococcus aureus. References: Bone and joint infections in children: acute hematogenous osteomyelitis. (http://www.ncbi.nlm.nih.gov/pubmed/26096866)

A 7-Year-Old Boy Is Brought to the Emergency Department Due