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NBME 16 Answers

nbme16/Block 2/Question#21 (8.8 difficulty score)
A 6-week-old boy is brought to the physician ...
Streptococcus pneumoniaeπŸ”,πŸ“Ί
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 +3 
submitted by cassdawg(1165),

HbS homozygosity indicates Sickle Cell disease. Streptococcus pneumoniae is associated with sepsis in patients with Sickle Cell (due to autosplenectomy causing increased risk of infections with encapsulated organisms) [FA2020 p136 and 422]

Streptococcus pneumoniae is susceptible to penicillin and prophylactic penicillin can decrease risk of infection.

Sickle cell patients would also be at increased risk of infection with E.coli, H. influenzae and neisseria (as they are encapsulated, p127) but they run less of a risk than Strep pneumo than causing sepsis in sickle cell patients. Salmonella is the most common cause of osteomyelitis in sickle cell patients but again is not what we would primarily be concerned with in this baby.

https://pediatrics.aappublications.org/content/141/3/e20172182

selectuw  I believe Staph is the most common cause of Osteomyelitis in Sickle cell but Salmonella commonly causes it in them more than the general population. +  
fruitkebabs  @selectuw You have it backwards, S aureus is most common overall, while Sickle Cell patients are more likely to have Salmonella Osteomyelitis (and S aureus as well). As a separate note, I thought the answer was Salmonella because Sickle Cell patients are functionally Asplenic beginning age 2-4 (Amboss) since it takes time for all the vessels in the spleen to get occluded and undergo necrosis, esp while HbF is still around in the first 6 months. Maybe that's why this question was taken out of active rotation? +3  
i_hate_it_here  This question was annoying. Sickle cell patients are at risk for all encapsulated organisms, and penicillin is not the main-stay treatment for any of these bugs. Only got this question right because S. pneumo was the only gram positive +3  
topgunber  think that was the purpose of the q honestly, they wanted you to pick salmonella for osteomyelitis, but logically penicillin's moa is targeting the only gram positive in the list. +2  
shieldmaiden  We also have to consider the patient's age; 6 weeks old. At this age, the encapsulated bacteria that can most commonly cause pneumonia is strep pneumo, and with HbS, it can lead to an invasive infection. Prophylaxis for newborns IS penicillin. The publication shared by cassdawg has that information and I also found it in UpToDate. +  



 +0 
submitted by shakakaka(4),

Why not N.meningitidis ? Penicillin and ceftriaxone are treatment chooses for N.meningitidis and it's encapsulated.. If I'm not mistaken macrolides and ceftriaxone are treatment for S.pneumo , not penicillin

shieldmaiden  This is prophylactic treatment, and penicillin is the one recommended by the AAP and CDC +