vyseerx
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4 years old male child was brought to the ER with complaints of pain in the right knee joint for 2 days. he was limping . on examination the joint was edematous ,erythematous and tender to touch. child was febrile and complained of chills. joint aspirate has shown leukocytosis , predominantly neutrophils. father tells that child was adopted at 2 yearsof age and the immunization status is not known.which is the most likely organism to have caused the child's illness?
a.staphylococcus aureus
b.Group A Streptococcus
c.Group B streptococcus
d.Haemophilus influenza
e.streptococcus pneumoniae
f.Group D Streptococci
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vyseerx
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| asmi
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its C
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| step1taker
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A.
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| alice8
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a.staphylococcus aureus
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| mjl1717
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ALL pathogenic bacteria can cause this,my tipoff is that the father doesnt know immunization status so I go with -d- Haemophilus influenza - :idea:
(Salmonella could have been in this differential)
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A - the most frequent cause
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| almina
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H influenzae type B was the most common cause prior to the widespread use of vaccines. The vaccine is used in the first year of life.
S aureus is now the most likely etiologic agent in children of all ages Answer - A
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| mjl1717
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USMLE would probably give a little more info then is in this q such as
1)Was the child adopted within or outside of the U.S.
2)Characteristics of the organism-is it haloduric(salt tolerant) or is their a
CAMP factor
3)Did the child have previous ds eg.?
4)Is the organism pleomorphic or fastidious?
5)**The qs are not a random lottery-in this q all we know is that
[a 4 year with questionable immunization status has septic arthritis.]
My complaint is that ther is No hint or tip,biochemistry Nothing.
Once again ANY pathogenic organism can cause that!!!
There is a method to asking qs for USMLE :shock:
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| vyseerx
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since it is mentioned that child's immunization status is not known, it must be assumed that it is not complete, and haemophilus infuenza is the correct choice as causative agent of septic arthritis in a 3 years old child!!
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| mjl1717
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In that case usmle would tell you the child was adopted from outside the U.S. or that it is an organism that grows in culture around staph aureus since staph aureus can produce NAD for this fastidious organism! :idea:
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how does staph.aureus produce NAD for H.influenza ?
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| mjl1717
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Haemophilus means blood loving , the "satellite phenomenon" occurs on blood agar-it grows around S.aureus since Staph produces NAD and lyses erythrocytes. Haemophilus requires NAD. Hope this helps
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