WBR0852

Author	[[PageAuthor::Mohamed Moubarak, M.D. [1]]]
Exam Type	USMLE Step 3
Main Category	Emergency Room
Sub Category	Infectious Disease, Infectious Disease
Prompt	An 11 year-old boy brought to the ED by his mother complaining of progressive severe pain, and swelling in his left foot. The mother said that she used some analgesic medications that were prescribed to him 2 weeks ago for fever after he injured himself during playing, but neither the pain nor the fever subsided. He is type I diabetes mellitus patient on insulin, taking no other medications. On examination, the patient is feverish with temperature 39 C (102 F), heart rate 100/min, blood pressure 140/80 mmHg, and respiratory rate of 22/min. His left foot is severely tender, red, and hot, with decreased range of motion on examination. You ordered x-ray which turned back with no pathology. You ordered a blood culture and prescribed the proper antibiotics. What is the most common organism causing this condition?
Answer A	Escherichia coli
Answer A Explanation	Incorrect Gram-negative bacteria are more common in some subpopulations, including intravenous drug users and splenectomized patients
Answer B	Pseudomonas aeruginosa
Answer B Explanation	Incorrect Gram-negative bacteria are more common in some subpopulations, including intravenous drug users and splenectomized patients
Answer C	Salmonella
Answer C Explanation	Incorrect Salmonella has been considered the principal causative organism of Osteomyelitis in patients who have sickle-cell disease. This patient doesn’t show any history of sickle cell anemia.
Answer D	Staphylococcus aureus
Answer D Explanation	Correct Staphylococcus aureus is the organism most commonly isolated from all forms of Osteomyelitis
Answer E	Mycobacterium tuberculosis
Answer E Explanation	Incorrect Osteomyelitis is a secondary complication in 1-3% of patients with pulmonary tuberculosis. The bacteria generally spread to the bone through the circulatory system, and tend to affect long bones and vertebrae. This patient didn’t show any history or significant symptoms to suggest tuberculosis infection
Right Answer	D
Explanation	Bloodstream-sourced osteomyelitis is seen most frequently in children, and nearly 90% of cases are caused by Staphylococcus aureus. In infants, S. aureus, Group B streptococci, and Escherichia coli are commonly isolated; in children from 1 to 16 years of age, S. aureus, Streptococcus pyogenes, and Haemophilus influenzae are common. In some subpopulations, including intravenous drug users and splenectomized patients, Gram-negative bacteria, including enteric bacteria, are significant pathogens Infants (< 1 year) Children (1 to 16 years) Adults (> 16 years) Group B streptococci S. aureus Staphylococcus epidermidis Staphylococcus aureus Streptococcus pyogenes S. aureus Escherichia coli Haemophilus influenzae Pseudomonas aeruginosa - - Serratia marcescens - - E. coli http://www.aafp.org/afp/2001/0615/p2413.html Educational Objective: References:
Approved	No
Keyword	[[WBRKeyword::Osteomyelitis]]
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