MRSA, MRSA me, Staph ain't what it used to be...

Apologies for the title, I couldn't help myself.  :)

ORSA comes up a lot, specifically how to decolonize patients with community-acquired ORSA (CA-ORSA). The UNC hospital epi people put together a brochure, which is sometimes hard to locate. I found this PDF online, from Kaiser Permanente out in California, which outlines I think what's pretty standard for us around here:

http://www.kplearning.com/10_national_site/uploads/B1S3.pdf

Johns Hopkins used to publish this nice periodic newsletter on HIV issues, but they've discontinued it due to time and budget constraints. Nevertheless, there was a nice article in the September 2004 edition that addressed CA-ORSA:

http://www.hopkins-hivguide.org/images/publications/nl_04_sept.pdf

The only caveat I'd put on this is, please know that the conventional dosing of TMP/SMX (Bactrim™, Septra™) at one DS tablet twice a day (as in the Hopkins thing) is now considered insufficient for ORSA treatment (at least around here, anyway). You need TWO DS tabs twice daily, and make sure you adjust for renal function, if reduced.

In general, we use doxycycline as our second-line agent, followed by clindamycin. Our micro lab will report clindamycin susceptibility separate from erythromycin – but outside labs may not be as reliable. Remember that CA-ORSA may have inducible resistance to the lincosamides (of which clinda is one) that won't show up in microdilution susceptibility testing used in outside hospitals and labs. You can't detect this is unless a "D-test" is performed, with both an e-mycin (15 µg)  and a clinda (2 µg) disk dropped onto the plate:

If the bug has inducible resistance, there'll be a flattening of the zone of inhibition between the two disks, suggesting that the bugs closer to the e-mycin disk have switched on their inducible resistance genes and are now laughing at the silliness of you attempting to use clindamycin to kill them.

Editorial note: The acronym "MRSA," for methicillin-resistant Staphylococcus aureus, is a humongo misnomer, since we don't use methicillin for resistance testing, and haven't in many years. Oxacillin is used on the plates, not methicillin – so you may hear it referred to more often in the micro lab as ORSA, and more often in the community as MRSA. If you're an ID purist, go with ORSA and look smart when someone asks what the hell it is that you're saying. (Or look like a big know-it-all dork. :)   )

 

– Christopher Hurt

Vancomycin

Our patients are frequently on Vancomycin, due to the increasing incidence of ORSA in both hospital-acquired infections, and community-acquired infections. ORSA can cause a variety of infections, and we commonly follow patients with ORSA pneumonia, cellulitis, deep soft tissue infections, abscesses, osteomyelitis, bacteremia and endocarditis. Vancomycin does also cover other gram-positives, but is the treatment of choice for ORSA infections. It is the treatment of choice in PCN-allergic patients with gram positive infections. There are several important things to remember when treating a patient with Vancomycin:

1. Weight and renal function (measured by GFR or creatinine clearance). Both will influence the therapeutic dosing of Vancomycin. Generally, Vancomycin is dosed 15-20 mg/kg, and given q12h hours in patients with normal renal function.

2. Vancomycin is not absorbed systemically when given orally. Therefore, po Vancomycin is only approved as second-line treatment of C. difficile colitis. Otherwise, it should ALWAYS be given intravenously.

3. Weekly labs. When on Vancomycin, weekly labwork should be checked and should include: CBC with differential, BUN and creatinine, and Vancomycin trough.

4. Goal troughs. Vancomycin is monitored via the collection of troughs, which should be drawn ~30 minutes prior to the next scheduled dose. In general, peak testing is unnecessary. The goal trough will depend on the site of infection (keeping in mind that these goals have been extrapolated from other data, and have yet to be verified in clinical studies):

1. Goal trough of 15-20 mcg/ml is reserved for Pneumonia, Endocarditis, Meningitis, and Osteomyelitis.


2. Goal trough of 10-15 mcg/ml is used for skin and soft tissue infections and Bacteremia.

5. Adverse Reactions.

1. "Red Man Syndrome." A systemic response to the infusion, that includes flushing and sweating. Is not dangerous, and is not an allergy. It can usually be remedied by slowing the infusion rate, and/or diluting the Vancomycin in a larger volume of solute.


2. Ototoxicity. Generally not reversible, and occurs at high levels.


3. Renal failure. Uncommon, except when Vancomycin is given concomitantly with other nephrotoxic agents. If a patient develops ARF while on Vancomycin, you can generally continue Vancomycin, making dose adjustments, while the cause of the ARF is being worked up.

***In terms of when we follow Vancomycin levels, we should follow Vancomycin levels on patients on which we recommended the use of IV Vancomycin when seen as an inpatient AND will follow up with you in ID Clinic. In cases where we do not plan to see the patient in follow up, the team should make arrangements for that patient's outpatient provider to follow labwork. You may volunteer to follow labwork on these patients if they have no provider to do so. BUT, you should NEVER follow Vancomycin levels or labs on patients whom you have not seen. We have been called to follow labs on patients being discharged from various services who are going home or to a SNIF on Vancomycin. The answer to this request should be a firm NO. It becomes a legal liability when following labwork on a patient you don't know and have never seen, and in whom you did not recommend Vancomycin in the first place. What if they develop an adverse drug reaction??? Who is responsible? On paper, you would be, as the ordering physician. So, keep that in mind. Most services have no staff in place assigned to follow labwork on patients on IV antibiotics, and remember, NEITHER DO WE. It is our responsibility as fellows to follow it on our patients only. We should not volunteer to do it as a service for the entire hospital. Just imagine how many labs we would be following if we monitored labs on every patient discharged on Vancomycin from UNC?!?! Please make requesting services aware of this.***

Yvonne Carter, MD

Antimicrobials Cheat Sheets/Primers

Back in residency, during long boring nights at The Miriam Hospital as a 3rd year night float, I decided to go and look up the mechanisms of the major (current) antibacterials, antifungals, and antimycobacterials. Here are links to those sheets, for your reference. The antibacterials one has been fairly widely circulated at Brown and here at UNC, so feel free to use it, mark it up, use it for teaching or for quick reference. The antifungals and antimycobacterials sheets are just plain Word documents, but the antibacterials one is a PDF.

http://www.unc.edu/~churt/downloads/Antibacterials_11-2005.pdf
http://www.unc.edu/~churt/downloads/Antifungals.doc
http://www.unc.edu/~churt/downloads/Antimycobacterials.doc

– Christopher Hurt

Tips for calling an ID consult

General Stuff

Please try to call us with new consults before 1:00 pm, as we go down to the microbiology lab for plate rounds at 1:30, and it's helpful to be able to see their plates, etc. while we're there.

Please don't call us for oral recs on the day of discharge, if at all possible. We don't like to hold up people's exit from the hospital when we tell you they need a PICC line and 2 weeks of bug juice.

HIV Patients

In 2007, the ID division requested from all admitting services that a special HIV consult be called for any and all patients with HIV admitted to UNC, on any team. The purpose of this is to reduce the number of errors in antiretroviral medications prescribed, and so that the clinic providers know their patient is admitted. Unless there's an ID issue you need help with, we'll usually leave a brief note outlining their ARV doses, and then not actively follow the patient. If you want us to follow them, please let us know that up front.

When you call us with one of these, please tell us why they're being admitted, what their most recent CD4 count and viral load are, who their clinic provider is (and if they're not followed here, where they go), and what antiretroviral medications they're taking (if any).

Helpful ID Pearls of Wisdom

The first rule of ID is, don't catch what they have. Don't be ashamed to go dig out a green N95 mask or put on a gown to go talk to a patient, if you don't know what their diagnosis is.

If you stick yourself:

(1) stop whatever you're doing,

(2) wash your hands with soap and water,

(3) call the occupational health clinic, at 966-9119 (or after-hours, 966-7890)

There is no data supporting the use of oral antibacterials for treating a bacteremia in adults - all of them require parenteral therapy, for at least 14d (assuming it's uncomplicated - no endocarditis, indwelling lines, etc.)

Staph aureus in the urine is ALWAYS A BAD THING. It should never be considered a contaminant, and you should call us to help with a general workup for an occult bacteremia.

If you have Staph aureus in the blood, they need an echocardiogram. We're always going to ask for one if you call us with a positive Staph aureus blood culture.

Coag-negative Staph (epidermidis) should always be considered oxacillin/methicillin-resistant (ORSE/MRSE), but doesn't require contact precautions.

For fevers of unknown origin, please make sure you really have no idea where it's coming from - so make sure you have a chest film, urine and blood cultures, and sputum cultures (if appropriate) cooking before you call us.

If you're calling for antibacterial recs, please try to have an idea of what they've been on to-date, when it was started, and the most recent culture data. Microbiology labs at outside hospitals are usually pretty friendly and helpful if you call for data.

If you think your patient has necrotizing fasciitis or a deep-seated tissue infection like pyomyositis, call general surgery FIRST and THEN call us. We'll help with antibacterials, but the treatment is ALWAYS surgical. Clindamycin for the first 72h of true nec fasc may save the patient's life by shutting off bacterial toxin production. Add it if you think they're not doing so hot - and then call us.

For TB rule-outs, you don't have to get sputum samples only from the first-thing-in-the-morning sputum - you can get 3 serial samples, if they're spaced at least 8 hours apart. One bronch sample counts for 3 induced or expectorated sputa.

For questions about contact precautions, etc., we're happy to help - but the best resource is actually hospital epidemiology, whose number is 966-1636. Someone's always on-call for them, too.

New antibacterials

Linezolid is a nasty medication, and shouldn't be used willy-nilly! It can causes a reversible, isolated thrombocytopenia in up to half of patients who receive it, and whole-marrow suppression in up to 25% of those on it. It also has MAOI-like properties, so drug-drug and drug-food interactions are significant - including serotonin syndrome if co-administered with SSRIs, and hypertensive crises if taken with some foods. If you have a question about whether or not to use it for a patient, just call us.

Tigecycline makes people ridiculously nauseous, and that's by far its limiting side effect. It cannot be used for bloodstream infections, since it's static and doesn't concentrate in the blood. Great for tissue, bad for blood.

Daptomycin causes rhabomyolysis, so you need to follow CPKs on patients while on therapy. It can be used for bloodstream infections, but not pneumonias - since lung surfactant inactivates the drug. Great for blood, bad for pneumonias.