WBR0852

Author

[[PageAuthor::Mohamed Moubarak, M.D. [1]]]

Exam Type

ExamType::USMLE Step 3

Main Category

MainCategory::Emergency Room

Sub Category

SubCategory::Infectious Disease, SubCategory::Infectious Disease

Prompt

[[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

AnswerA::Escherichia coli

Answer A Explanation

[[AnswerAExp::Incorrect

Gram-negative bacteria are more common in some subpopulations, including intravenous drug users and splenectomized patients]]

Answer B

AnswerB::Pseudomonas aeruginosa

Answer B Explanation

[[AnswerBExp::Incorrect

Gram-negative bacteria are more common in some subpopulations, including intravenous drug users and splenectomized patients]]

Answer C

AnswerC::Salmonella

Answer C Explanation

[[AnswerCExp::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

AnswerD::Staphylococcus aureus

Answer D Explanation

[[AnswerDExp::Correct

Staphylococcus aureus is the organism most commonly isolated from all forms of Osteomyelitis]]

Answer E

AnswerE::Mycobacterium tuberculosis

Answer E Explanation

[[AnswerEExp::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

RightAnswer::D

Explanation

[[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