1. S. aureus subtypes based on Methicillin resistance
Methicillin resistant Staphylococcus (MRS)
SNOMED Grouper
Used clinically?
Parent for MRSA, MRSI, MRSP
Methicillin susceptible S. aureus (MSSA) – Rarely used, not in SNOMED
Methicillin resistant S. aureus (MRSA)
Multi-resistant S. aureus (mMRSA)
Non-multi resistant S. aureus (nmMRSA)
Methicillin resistant Staphylococcus (MRS) -This Is not a commonly used term (in the literature at least) so far as I can tell. Serves as parent for Methicillin resistant S. aureus, Methicillin resistant S. intermedius and Methicillin resistant S. pseudointermedius. This may be a useful grouping term but it may also simply be evidence of “defined by inheritance” (rather than attributes and values) prevalent in primitive hierarchies like Organisms.
Methicillin susceptible S. aureus (MSSA) - S. aureus susceptible to (the penicillinase-resistant penicillin) methicillin.
Methicillin resistant S. aureus (MRSA) - S. aureus resistant to methicillin. Also called oxacillin-resistant S. aureus (ORSA).

2. Methicillin resistant S. aureus subtypes
Multi-resistant S. aureus (mMRSA)
Non-multi resistant S. aureus (nmMRSA)
Multi methicillin resistant S. aureus (mMRSA) - S. aureus resistant to methicillin and multiple other drug classes. No specific definition of the degree of “other” resistance has been found in the literature (more than 2 other antibiotic classes? more than 3 other antibiotic classes?). AKA multi oxacillin resistant S. aureus (mORSA)
Non-multi methicillin resistant S. aureus (nmMRSA) - S. aureus resistant to methicillin but resistant to fewer other drug classes the mMRSA strains. No specific definition of the number of “other” class resistance has been found in the literature (fewer than 2 other classes? Fewer than 3?) AKA non-multi oxacillin resistant S. aureus (nmORSA)

3. S. aureus infection subtypes based on source of infection
Community acquired S. aureus
May be MSSA, mMRSA, nmMRSA
Hospital acquired S. aureus
Community acquired S. aureus - S. aureus infecting or isolated from a patient infected in a natural (community) setting. May be MSSA or MRSA.
Hospital acquired S. aureus - S. aureus infecting or isolated from a patient infected in a medical (hospital or clinical) setting. May be MSSA or MRSA.

4. Related disorder/finding content
| Methicillin resistant Staphylococcus aureus infection (disorder)
| Community-acquired methicillin-resistant Staphylococcus aureus infection (disorder)
| Methicillin-resistant Staphylococcus aureus infection of postoperative wound (disorder)
| Sepsis due to methicillin resistant Staphylococcus aureus (disorder)
| Pneumonia due to methicillin resistant Staphylococcus aureus (disorder)
| Bronchopneumonia due to methicillin resistant Staphylococcus aureus (disorder)

5. Existing content MRSA = Methicillin resistant S. aureus
MSSA = Methicillin susceptible S. aureus
mMRSA = Multi-methicillin resistant S. aureus
nmMRSA = Non-multi methicillin resistant S. aureus
CA- = Community acquired
HA- = Hospital acquired

6. Add requested content? - YES
I think this is not controversial. We have no approved model for resistance to specific antimicrobials. Alignment with observables model should not be too difficult. HOWEVER, modeling the fact of “multi (class) resistance” and “non-multi (class resistance) is more challenging. First it will likely depend on concrete domains (e.g., resistance to more than N classes) and second there is no clear definition of the number of additional antimicrobial classes that would distinguish mMRSA and nmMRSA.
Proposal: We add the “more specific” mMRSA and nmMRSA (primitive) classes as descendants of existing (primitive) MRSA class. Modeling can be done when/if a model is developed and specified.

7. If all of these classes were represented in the organism hierarchy:

8. What to do with Community Acquired and Hospital Acquired MRSA
Option 1 – Retire
| Community acquired methicillin resistant S. aureus
| Hospital acquired methicillin resistant S. aureus.
Refer both (MAY BE) to | Methicillin resistant S. aureus.
Option 2 – Leave them in the hierarchy as descendants of MRSA and siblings of mMRSA (new) and nmMRSA (new)
Option 3?
We do not have enough laboratory user input. It is not clear whether CA and HA classes are being used or are needed.

9. Retirement
The existing relationship(s) remain true. The two retired concepts are MRSA. The ambiguity is revealed by the distinct “may be” classes.