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  #1  
Old 03-15-2011
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Arrow Practice Question, Microbiology #3

A 3 yr old male patient with the following findings on a blood smear is most susceptible to infection by which of the following species?

A. Staphylococcus aureus
B. Pneumocystis jiroveci
C. Streptococcus pneumoniae
D. Streptococcus pyogens
E. Neisseria meningitidis
F. Salmonella typhi

Practice Question, Microbiology #3-nospleen.jpg
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  #2  
Old 03-15-2011
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Umm I want to say
C - Strep Pneumonia

I would say this because..it seems as if there are remnants in the RBCs - howell jolly bodies...pretty much seen in patients with sickle cell (asplenia)...which leads them to encapsulated organism infections..and since this is a 3 year old..I am going to go with Strep Pneumonia being the most common in that age group.
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  #3  
Old 03-15-2011
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Quote:
Originally Posted by Cautie Pie View Post
Umm I want to say
C - Strep Pneumonia

I would say this because..it seems as if there are remnants in the RBCs - howell jolly bodies...pretty much seen in patients with sickle cell (asplenia)...which leads them to encapsulated organism infections..and since this is a 3 year old..I am going to go with Strep Pneumonia being the most common in that age group.
Neiserria is also encapsulated, so that wouldn't help much. But you are correct on S. Pneumonie being more common in 3 year olds.

Sucks this question doesn't come with more history.

I'd go with S. Pneumonia aswell. Since if this was a case of N. Meningitidis, you'd have done a CSF exam instead of blood smear lol
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Old 03-15-2011
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Quote:
Originally Posted by patelMD View Post
Neiserria is also encapsulated, so that wouldn't help much. But you are correct on S. Pneumonie being more common in 3 year olds.

Sucks this question doesn't come with more history.

I'd go with S. Pneumonia aswell. Since if this was a case of N. Meningitidis, you'd have done a CSF exam instead of blood smear lol
I did not choose N. Meningitidis (even it being encapsulated) is because its more in the 6-60 yr old range. S. Pneumonia is the most common overall and it being a sickle cell patient made me more attracted to choosing S. Pneumonia.
But I don't think I can assume it has to be meningitis..I don't know why but I just knew that S. Pneumonia has been mentioned a gazillion times related to sickle cell, I guess N. Meningitidis could be as well since its encapsulated but I guess its not as common as S. Pneumonia.
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Old 03-15-2011
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I'll also go with C. Strep pneumo.
Although asplenia is frequent in sickle cells disease due to autosplenectomy, this usually occurs later in childhood. Notice those are spherocytes and indeed, some Howel-Jolly bodies are seen. So my diagnosis would be Spherocytosis, probably after therapeutic splenectomy, which increases susceptibility to encapsulated organisms, more likely Strep. penumo in a 3 y/o.
Btw... the picture's filename is nospleen.jpg... lol
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Old 03-16-2011
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Correct Answer C is correct!

Good job guys!

I got lazy with this question and didn't come up with a better patient history but the point I wanted to make was that in a patient without a spleen, you will see Howell-Jolly bodies and that infection with Strep pneumoniae is very common.

Another infection to keep in mind in patients w/o a spleen is osteomyelitis caused by Salmonella.
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Old 04-09-2011
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neiserria meningitidis...
as an encapsulated bacteria...
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Old 04-09-2011
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this is my first post here i would say it is right that sickle cell patient would have autospleenoctomy but not in a 3 years old patient so i would take salmonella as better choice and i would like to know what you think about that thank you all
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yes..thats right.. I didn't read all answers completely... and just didn't see pneumococci!! thats right..pneumococci is a better answer...
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Quote:
Originally Posted by dr.muhamad View Post
this is my first post here i would say it is right that sickle cell patient would have autospleenoctomy but not in a 3 years old patient so i would take salmonella as better choice and i would like to know what you think about that thank you all
Salmonella would be the correct answer if the question specifically asked about osteomyelitis, but respiratory infections are wayyyy more frequent in an asplenic patient. And again, those are spherocytes NOT sickle cells.
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yes..clearly there were lots of spherocytes... it could b a case of hereditary spherocytosis for him, splenectomy was done...
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Originally Posted by jorgemorales View Post
Salmonella would be the correct answer if the question specifically asked about osteomyelitis, but respiratory infections are wayyyy more frequent in an asplenic patient. And again, those are spherocytes NOT sickle cells.
yes you are right man those are spherocytes and they aren't asking if it is respiratory infection or osteomylitis
so what would you say?
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so..now we should think of encapsulated organisms.. strep pneumo and neiseria,,

but you know..it doesn't mention about the vaccination history.. if the pt is vaccinated against pneumococci, you can think of neisseria.. otherwise, pneumococci is the most probable organisms...
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I have a question.. It doesnt say anything about vaccination history.... most pts are vaccinated against pneumococci... but N. meningitis is not part of routin vaccination... if the pt is immune against pneumococi, can it b neiseria?
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I have a question.. It doesnt say anything about vaccination history.... most pts are vaccinated against pneumococci... but N. meningitidis is not part of routin vaccination... if the pt is immune against pneumococi, can it b neiseria?
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Quote:
Originally Posted by dr.muhamad View Post
yes you are right man those are spherocytes and they aren't asking if it is respiratory infection or osteomylitis
so what would you say?
Precisely, if they are not specifying, then the most likely pathogen for an infection in an asplenic pt would be Streptococcus pneumoniae.

And yes, this is most likey a pt with Hereditary Spherocytosis after surgical splenectomy.
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Originally Posted by daniyel View Post
I have a question.. It doesnt say anything about vaccination history.... most pts are vaccinated against pneumococci... but N. meningitis is not part of routin vaccination... if the pt is immune against pneumococi, can it b neiseria?
From my understanding, the vaccination against pneumococcus will increase titers of antibodies against the capsule of this bacteria. Normally, these encapsulated organisms are cleared from the circulation by phagocytes by macrophages in the spleen. When the spleen is not present, these encapsulated organisms are much more difficult to clear from the blood.

Using this logic, even thought the vaccine is protective, it may not be very effective in patients without a spleen because of the difficulty in clearance.

The concept I was trying to test with this question was the high incidence of Strep pneumoniae infection in patients without a spleen (Howell-jolly bodies are indicative of asplenia)

Here is something I found from Wikipedia:

The spleen contains many macrophages (part of the reticuloendothelial system), which are immune cells that phagocytose (eat) and destroy bacteria. In particular, these macrophages are activated when bacteria are bound by IgG antibodies (IgG1 or IgG3) or the complement component C3b. These types of antibodies and complements are immune substances called opsonizers, molecules that bind to the surface of bacteria to facilitate phagocytosis.
When the spleen is no longer present (asplenia), IgG and C3b are still bound to bacteria, but they cannot be removed from the blood circulation due to the loss of the splenic macrophages. Hence the bacteria are free to cause infection.
Patients without spleens often need immunizations against pathogens that normally require opsonization and phagocytosis by macrophages in the spleen. These include common human pathogens with bacterial capsules (Streptococcus pneumoniae, Salmonella typhi, Neisseria meningitidis, E. coli, Hemophilus influenzae, Streptococcus agalactiae, Klebsiella pneumoniae). Capsules made of polysaccharides (sugars) are an evolutionary development by bacteria to evade phagocytosis by macrophages alone, since only proteins are directly recognized by macrophages in phagocytosis. So humoral immunity in forms of IgG and complement proteins is the human immune system's response against bacterial capsules.
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