Few things learned today…
Causative organisms and imaging
– Staphylococcus aureus is not a common cause of CAP, but one is at higher risk if a patient had influenza prior to developing a pneumonia
– S. aureus pneumonia can be correlated with cavitations (indicating an abscess) on a CXR…but then again, cavitations could also reflect group A strep or S. pneumoniae pneumonia.
– Combined with risk factors of course, Pseudomonas aeruginosa pneumonia could be gathered by bronchiectasis on the CXR
Edit (Nov 3rd, 2017): More pneumonia radiography and clinical pearls:
– Anatomically, the right side of the bifurcation from the trachea is superior to the left side…so naturally, bacteria take the path of least resistance and end up in the right lower lobe for the typical consolidation one sees on the CXR
– The CXR will usually lag behind clinical signs and symptoms by a day…so if a patient is a quick presenter to ED, sometimes you can’t visualize the consolidation until you repeat the CXR a day later!
– Depending on local resistance rates, at St Paul’s, levofloxacin covers Pseudomonas, and usually a cipro susceptible strain will be levo susceptible (levofloxacin has the added advantage of covering usual CAP bugs whereas cipro poorly covers Streptococcus pneumoniae).
– The reverse cannot be said – levo susceptible strains are not necessarily cipro susceptible
– Cipro resistant strains may be levo susceptible…but you will need to call your micro lab to get that info.
Atypical coverage is only warranted if one feels that the host immune system will not be able to overcome such an infection, such as in the case of immunocompromised patients, or those with structural lung disease.
Beta-lactams and coverage of a CAP
– High-dose amoxicillin (1 g PO TID) is only recommended if intermediate Strep is suspected…and local resistance rates indicate that it is not a worry here
– Risk factors for a beta-lactam resistant Strep pneumo: patient <2 or >65 yo, beta-lactam therapy within last 3 months, alcoholism, medical comorbids, immunosuppressed, exposure to child in daycare centre.
– For outpatients only: amoxicillin, amoxi/clav, cefuroxime are all acceptable alternatives. IDSA guidelines recommend adding a macrolide or doxycycline for atypical coverage, but practically, only if immunocompromised or structural lung disease is present.
– For inpatients: cefotaxime, ceftriaxone, ampicillin. Respiratory FQs ONLY USED FOR TRUE BETA-LACTAM ALLERGY.
Haemophilus influenzae can produce beta-lactamases. Which cephalosporins and penicillins overcome these enzymes?
– Cefuroxime is more active than cefazolin to H. influenzae and M. catarrhalis that produce beta-lactamases
– 3rd generation cephalosporins are distinguished by stability against beta-lactamases of Gram-negative bacilli
Ceftaroline is a 5th gen cephalosporin with activity against MRSA, VISA, and S. pnuemoniae resistant to penicillin or CTX. It does NOT cover ESBL, Pseudomonas aeruginosa, Acinetobacter baumanii, or B. fragilis