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NBME 20 Answers

nbme20/Block 2/Question#8

Three elderly residents of an assisted living ...

Legionella pneumophila

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submitted by usmle11a(36),

legionella : very common in advanced age, COPD, immunosuppressed patients and " going back from a residence hall" which probably had a contaminated AX system (basically fits every one in the Q)

adeno X : would present with conjunctivitis, throat pain ... flu virus: not everyone got the disease RSV: no children strep pneumo: would target a larger population of healthy people as well.

bharatpillai  why would they say that the only people who didnt get affected by the disease were people on steroids (lupus nephritis and severe asthma) couldnt have been rsv since it causes croup in children. strep pneumo would cause fever and other systemic signs. i went for adenovirus because uworld says most common causes of copd excacerbation are viral infections... +1  
brbwhat  I went for adeno forr the same reason. I guess the MAIN HINT is that this is not a copd exacerbation. Since people without prexesting copd also had pneumonia, also people with copd exacerbation will have different presenting symptoms, here it was told, that we are told that dx was penumonia. People with copd exacerbation wouldn’t be diagnosed with pneumonia if it was an adenovirus infections. +1  

Legionella is common causes of pneumonia superimposed on chronic obstructive pulmonary disease.

asapdoc  Im pretty sure so is strept pneumoniae +2  
usmleuser007  COPD is also exacerbated by Viral infection: Rhinovirus, influenza, parainfluenza; and Bacterial infection: Haemophilus influenzae, Moraxella catarrhalis, Streptococcus. however, the questions gives a hint that it may be legionella = "weekend retreat" which may be associated with this infection +2  
loopers  From FA 2017 pg 139: Legionnaires’ disease—severe pneumonia (often unilateral and lobar A ), fever, GI and CNS symptoms. Common in smokers and in **chronic lung disease.** +1  
kentuckyfan  I also believe that the other attendees showed signs of pontiac fever, which is another hint they tried to get at. +2  
luke.10  i did it wrong and chose influenza virus since it is most common infection in COPD but the clue in the Question is that the other attendee didnt get sick since in legionella there is no person to person transmission +  
endochondral   but in Uworld s. pneumo is one of the most common bacterial exacerbation of COPD legionella wasn't even mentioned. How do we rule out s. pneumo ? +3  
nala_ula  maybe because in children s.pneumo causes otitis media? +  
smc213  Another hint made in the Q stem is the location being rural Pennsylvania.... Legionnaires disease was first discovered by the outbreak in 1976 at a convention held in Philadelphia, Pennsylvania. Not sure why I know this fact... +4  
hpsbwz  Biggest hint towards legionella to me was that they all were at a residence hall... i.e. where there'd be air conditioners and such. +4  

formatting got messed up and now its unreadable - lets try again

legionella because it's an environmental source (residence hall), no person to person transmission, SUPERIMPOSED pneumonia (NOT a COPD exacerbation)

common bacteria for superimposed - H. flu, legionella, morexella catarrhalis (pathoma)

COPD exacerbations usually described as progressively worsening dyspnea and cough, change in sputum; more often viral than bacterial/fungal (UW)

+1/- lynn(1),