Effect of Nonpayment for Preventable Infections on SSI Rates Following Orthopedic Procedures

The debate regarding the effect of CMS's 2008 policy denying incremental payment for 8 complications of hospital care, also known as never events, is ongoing. Some studies have identified reductions in CLABSI and CAUTI after the policy was implemented, while others failed to find reductions in CLABSI, CAUTI or VAP, using a different dataset and methodology.  The impact of the nonpayment policy change on orthopedic procedures is less well studied.

Authors Jereen Kwong and colleagues published a study in the July ICHE that examined the effect of the policy on SSI following spine fusion, shoulder and elbow arthrodesis and repair, and spinal refusion procedures, but not hip and knee replacements (since they aren't covered under the policy). To determine the impact, they analyzed 20% of all inpatient discharges among patients ages 60 to 80yo using the HCUP National Inpatient Sample from 2000 to 2013. This is an all-payer sample in that it covers patients where Medicare is the primary payer but also non-Medicare populations.

The authors' primary hypothesis was that if the CMS policy had an impact, we would see larger reductions in SSI rates among Medicare vs control, non-Medicare patients. You can probably sense my concern immediately. How would bundles implemented to reduce SSI only have an effect on Medicare patients? It is unlikely that infection preventionists or clinicians would even have knowledge of their payor status. If non-Medicare controls have had the same exposure, they can't be used as controls!

Without getting into the methods details, the authors were expecting larger changes in SSI rates in the Medicare vs non-Medicare populations and they didn't find significant differences RR=0.9, 95% CI 0.8-1.1)  Looking at their Figure 1 below, we can see that SSI rates were slightly higher in Medicare populations (dashed line) vs non-Medicare populations before and after the non-payment policy went into effect. If I were to do this analysis, I would have looked for a change in intercept and/or slope in the SSI rates before vs after the policy combining both payor populations. Looking at the figure, there doesn't seem to be much change after the policy went into effect in either group. So we can agree with the authors that the policy had limited or no impact on SSI rates, but not for the reasons the authors state.

On the positive side, SSI rates have been declining over the entire 14-year study period - so surgeons and infection prevention folks can pat themselves on the back. Keep on doing whatever you've been doing!

SSI Prevention Bundle in Cardiac, Hip, and Knee Surgery - A Home Run

...and I'm being modest...

As I mentioned yesterday, it's really hard to write a post when you've already written the accompanying editorial. Today, I have a taller task - posting on a study led by two close colleagues (and favorite people), Marin Schweizer and Loreen Herwaldt. (COI alert) Fortunately, JAMA Associate Editor, Preeti Malani, has done the heavy lifting with her excellent editorial.

In today's JAMA, Schweizer and colleagues reported the results of an AHRQ-funded trial examining the benefits of an SSI prevention bundle in orthopedic and cardiac surgery. The bundle was outlined in a meta-analysis they published in BMJ two years ago and included preoperative nasal screening for MRSA/MSSA, mupirocin BID and daily CHG baths for 5 days if screen positive and vancomycin added to perioperative prophylaxis if MRSA positive. The quasi-experimental intervention study took place in 20 US hospitals across 9 states with 39 months of pre-intervention SSI rates and 21 months of rates collected during the intervention period.

Overall, the results are impressive (i.e. not modest). First, there was a 42% reduction in SSIs after the intervention was implemented (see Figure, below), despite modest bundle adherence (39% full adherence, 44% partial adherence).

The key finding for me relates to the number of months where there were ZERO SSIs across all 20 hospitals. Looking at the Figure above, you can see that "the number of months without any complex S aureus SSIs increased from 2 of 39 months (5.1%) to 8 of 22 months (36.4%; P = .006 by Fisher exact test)." Seven times as many zero-months in all 20 hospitals. That's not a modest finding. ;)

Key points from the editorial:

"inclusion of patients undergoing emergency or urgent operations, a population recognized as at high risk for SSI, improves the generalizability of the findings."

"the primary study outcome was limited to complex S aureus SSIs, eliminating much of the subjectivity of infection surveillance. Even though surveillance practices varied among participating hospitals, complicated S aureus SSIs are not clinically subtle and can be identified easily by any surveillance system."

and given the modest adherence to the bundle, "Moving forward, efforts to promote and maintain adherence to prevention protocols will remain important"

"The study’s setting is among its limitations. All 20 study sites were from a single health care system with a well-established quality improvement infrastructure - certain factors in this health care system may differ from other clinical settings, including a below-average baseline infection rate. It remains unclear what challenges and barriers may present as this bundle is implemented at other institutions. Further studies in different settings will offer additional guidance."

and my favorite quote:"Although getting to zero is unlikely to be achievable, efforts that move closer to this elusive goal hold tremendous value for clinicians, hospitals, payers, and, most importantly, patients."

My final thoughts:
This is a wonderful study that took many years of planning, hard work and tremendous collaborators, including HCA and Ed Septimus. Congrats to all involved. Not every study is a grand slam, but we'll take a home run for infection prevention.

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

Rhinoceroses and Total Hip Arthroplasty

Distinctions are very important. I was just visiting Ohio last week and had the chance to visit the Columbus Zoo. It's a pretty cool place if you like zoos. I enjoyed reading about various animals and learned that the Black Rhino is endangered, while the White Rhino is not. Thus, it would make sense to spend your conservation money, if you have some, on Black Rhinos first, since time is running out. In infection control, we ought to do the same thing, but in reverse; spending our limited resources on preventing more common infections first. Also, with the rise of public reporting and other methods of interhospital comparison, efforts must be made to place hospitals on a level playing field. There is a nice study that highlights these two issues in the May ICHE by Surbhi Leekha and colleagues at the Mayo Clinic in Rochester, MN.

They examined at a 5-year cohort (2002-2006) of all total hip arthroplasties (primary and revision) and looked to see who developed SSI, using CDC definitions. After controlling for age, gender and NNIS index, patients who had a revision total hip arthroplasty had twice the odds of SSI compared to primary surgery (OR=2.2, 95% CI 1.3-3.7). The difference was even more stark when outcomes were restricted to deep or organ space SSI with revisional surgery associated with four times the odds of SSI (OR 3.9, 95% CI, 2-7.9). One note, they didn't appear to control for duration of surgery as a confounder, even though it was associated with both revisions and SSI. I think this is correct. They were not completing a risk-factor study, but were interested in outcomes.

The usual caveats apply to these types of studies including a single center study and a relatively unique single center at that. However, this is an important study and if these findings hold up at other institutions, which they most certainly will, this suggests that the case-mix of revision and primary hip arthroplasty must be taken into account when SSI rates are reported and hospitals compared. Perhaps an easier solution, as the authors suggest, is to treat them as two different animals, if you will, and report them separately. Also, if one wanted to target specific infections or high-risk procedures, these results suggest targeting revision surgeries over primary ones.

Note: Surbhi is joining the group at my old Maryland stomping grounds and I know everyone is excited for her to arrive.