Using viruses to detect bacteria!

The FDA just approved a new rapid detection test for MRSA and MSSA from blood cultures that are positive for Gram positive cocci (GPC). The most widely used tests for rapid MRSA or Staphylococcus aureus detection from blood cultures are real-time PCR tests by BD and Cepheid. These tests are limited by both cost and by some performance issues, one of which I referred to here.

The interesting thing about the new Microphage test is that it utilizes bacteriophages specific for S. aureus. The advantage of the test is that it is a simple immunoassay, requiring no special equipment or platform—the immunoassay detects phage antigens, which accumulate only if their target (S. aureus) is present. The MRSA/MSSA distinction is made in a similar manner, but using cefoxitin to inhibit the MSSA that the phages would otherwise feast upon. From the data in the package insert and in this ICAAC abstract from last year, the main limitation is a sensitivity of 91.8% for detection of S. aureus. If the result is positive for S. aureus, the assay is very accurate for distinguishing MRSA from MSSA (accurate enough to meet FDA standards for any commercial susceptibility test). So positive results should be useful, while negative results may not be (negative predictive value will vary based upon the proportion of all blood cultures positive for GPC that are S. aureus).

I could find no peer-reviewed literature on this test (point me to it if you can find anything), so we’ll have to see if real-life performance matches the trial data presented in the package insert. Cost will also be a big issue, and my understanding is that they haven’t settled on a price at this point.

Regardless of how it pans out, you have to love the concept of using bacteriophages for diagnostic purposes…compared with our nucleic acid detection tests, proteomics, etc., it just seems so…..old school!

No MRSA on Gym Equipment!?!

Modern Torture Devices

Some days when I'm tired, I don't feel like going to the gym. As someone who follows the IC literature, I always had a ready excuse for myself and others if I didn't want to go.  Too risky!  I don't want to catch MRSA, haven't you read the papers?

So I was depressed when I saw the headline this morning about a new study in AJIC from the University of Florida that found no MSSA and no MRSA on gym equipment surfaces before or after routine cleaning. They sampled 3 gyms (private, high school and university) on 3 separate occasions and obtained 240 samples. They swabbed gyms mats, benches, dumbells, cardio machines and weight machines. Oh well, back to the drawing board...and back to the gym.

Kathleen Ryan et al. AJIC March 2011

The Suncoast News - March 9, 2011

My surgeon has S. aureus!

Don't panic! Just based on probability a surgeon would have a 30% chance of being colonized with MSSA and perhaps a 1% chance of being colonized with MRSA. Researchers at NYU Hospital for Joint Diseases recently screened a total of 135 orthopedic surgeons for MRSA and MSSA nasal colonization. In the 74 attendings, 2.7% were MRSA+ and 23.3% were MSSA+. The story was a bit more interesting in the 61 residents with 59% MSSA+ and none MRSA colonized. Overall, 36% were MSSA+ and 1.5% were MRSA+, which is about what we would have guessed before the study.

These results are similar to Cecilia Johnston's report of healthcare worker colonization at Johns Hopkins a few years ago. She reported 28% S. aureus colonization (95% confidence interval [CI], 22%‐34%) and 2% MRSA colonization (95% CI, 0.04%‐4.0%). I pasted in Cecilia's results to highlight the fact that she calculated confidence intervals for each proportion. The NYU researchers were surprised by the high proportion of residents with MSSA colonization. Sure, the level was high, but if they would have calculated the 95% CI, which was 46%-71%, they might have been less excited.

It's possible that the long hours spent in direct patient care might be risk factors for MSSA colonization, as would frequently performing dressing changes, but these would not be unique to ortho residents. Perhaps they should repeat the study in the same residents at a later point to determine what proportion is transient vs persistent colonization. Of course, it would be nice to repeat the study in other cohorts of ortho residents and ortho nurses.

They also reported that patients screened prior to THR, TKR and major spine surgery at their hospital had 2% MRSA and only 18% MSSA colonization. It would have been nice to read more information about these patients, such as recent antibiotic exposure.

Schwarzkopf et al. in Journal of Bone and Joint Surgery (America): PubMed or JBJS
Johnston et al. in December 2007 ICHE
Easy confidence interval for proportion calculator: link

MRSA active surveillance: It just doesn't make sense

A study in the June issue of Infection Control and Hospital Epidemiology takes a look at staphylococcal colonization in healthcare workers. Over 250 HCWs were cultured and nearly half (44%) were colonized with S. aureus. MRSA colonization was found in 7% overall and was highest in nurses (10.5%). If the findings of this study are generalizable to other hospitals, this study has two important implications. First, given that nearly half of HCWs were colonized with S. aureus, hand hygiene practiced at very high levels of compliance is warranted. It seems that in the hysteria surrounding MRSA it's been forgotten that MSSA is also a pathogen. Second, why should hospitals engage in active detection and isolation (ADI) when non-patients are a significant reservoir for MRSA in the hospital setting? For those who continue to truly believe in ADI it seems that to me that their logic should dictate that MRSA colonized HCWs be removed from practice. And then there are visitors who may be colonized. The solution there could be to ban all visitors to the hospital. Of course, all of this assumes that the ADI zealots are driven by logic. Here's my recommendation: let's stop focusing on who has what organism (see Eli's posting from a few days ago), and just get everyone to wash their hands before and after every patient contact. The key word here is every. And maybe if that happened, we wouldn't need contact precautions any more. Now here's an interesting thought experiment: what could we do with all the money that's been spent on MRSA surveillance cultures over the last 5 years?

What if all S. aureus was MRSA?

We spend so much time discussing MRSA. We debate, we mandate, and we worry. Frankly, I'm getting tired of it. I'm far more worried about MDR-Gram negatives and all that oil spilling into the Gulf. So, while I was at the Orioles game today with my son, my mind drifted into an absurd thought experiment. To be clear, I'm a big baseball fan and I was trying to pay attention, it was just really boring until the O's scored 5 runs in the 8th, including a grand slam, to win it 6-5.

So as my mind drifted like the (three!) dingers Millwood was allowing, I thought: What if I could magically turn all S. aureus into MRSA? Now, I could have easily dreamed that all S. aureus would become penicillin sensitive, but I prefer to dream possibilities. What would this counterfactual world look like and why would I have such a thought? Would the world end? No. I know MRSA is the SUPERBUG, but I suspect the world would look as it does, but with a few differences; some good and some bad.

Now we all "know" that MRSA is more virulent than MSSA and leads to higher rates of mortality. Do we? I was a co-author on a meta-analysis, one that you must be required to reference if you publish on MRSA, since it's been cited >500 times. We found that MRSA bacteremia was associated with twice the odds of death compared to MSSA. I don't believe it. Never did. It's not that I don't think it was a great study; it was and is. It's just that since (fortunately) you can't randomly infect patients with MRSA or MSSA, you can never really study the clinical impact of MRSA. Since MRSA patients are sicker at baseline, before they even get infected, and vancomycin is a poor antibiotic, it is likely that MRSA just appears more virulent. If you give patients with MSSA vancomycin, they would do as poorly as those who were infected with MRSA.

Another reason that I'm not worried about an all MRSA world is that we have plenty of treatment options for MRSA unlike MDR-GNR. More are likely in the pipeline. The one downside I think of an all MRSA world is that it would be more expensive to treat infections since many of the treatment options would be more expensive. We would also have new abbreviations to learn: LRSA or DRSA (linezolid or daptomycin), etc. Yes, I know VRSA.

So far, I suspect I've put you to sleep, much like I was during the first seven innings of today's game. But here's my point. There would be a very important upside to this all methicillin resistant, Staphylococcus aureus world. It would mean that hospital epidemiologists and clinicians, patients and societies and legislators and journalists and everybody...could stop worrying about MRSA and start worrying about plain old S. aureus. What? Yes! We could isolate, treat, worry about, write about, legislate and actually deal with all patients with Staph aureus the same way. Since all S. aureus would be "the same" - which it really is, we've just forgotten that MSSA and PCN-sensitive SA are so deadly.

So there you have it. We could look to prevent ALL Staph infections, not just MRSA ones, since they would all be MRSA in this new world. And since MRSA is likely not worse than MSSA, no one would be worse off and I suspect many would be better off because we could target for prevention the 99% or 70% or 50% of infections caused by S. aureus that we currently ignore. And better yet, we could do this now. We don't have to wait for this 100% MRSA world. We could stop this MRSA insanity and actually target all S. aureus infections, or dare I dream, all hospital pathogens: resistant or sensitive, Gram-positive or Gram-negative (or C. diff). Alas...

Go Orioles. (Who says a guy can't dream...)