MRSA reductions in ICUs – good news, but qualified

Constant readers, you will no doubt have seen the overnight news about a paper by CDC authors in the Journal of the American Medical Association, reporting a significant decline in catheter-associated bloodstream infections (known by the uncatchy acronym CLABSIs, and yes, people pronounce it “klab-seez”) in intensive care units.

Our results show that the 6 most common adult ICU types reporting central line–associated BSIs to the CDC, which together account for 96% of all reported MRSA central line–associated BSIs among studied ICU types, have experienced declines of 50% or more in the incidence of MRSA central line–associated BSI since 2001. This means that the risk of primary MRSA bloodstream infections among patients with central lines in these ICUs has substantially decreased in recent years.

First, let’s stipulate that any reduction in healthcare-associated infections is good, good news.

Having said that, let’s drill down into the paper a bit. Because in some of the coverage last night and this morning, this paper is being represented as “Hooray, the MRSA problem is over,” and that’s an over-reaction. Here are some reasons why.

The data come from several overlapping CDC databases: the National Nosocomial Infections Surveillance system (NNIS) and the National Healthcare Safety Network (NHSN). The NNIS existed from 1970 to 2004; there was a data gap in 2005, and the NHSN sprang up in 2006. There were 300 hospitals in 37 states reporting to the NNIS when it shut down, and in 2007 there were 518 reporting to the NHSN, many of which joined that year as a result of new mandatory HAI reporting in New York, Colorado and South Carolina. Participation in either database was/is voluntary.

The CDC analysis abstracts data from the reports to those systems for the years 1997-2007. But, as you can guess from those numbers above, the data does not cover all 7,500 US hospitals; and because it is more weighted to certain states, it does not represent a nationally representative sample. In addition, hospitals came into the system(s) during the study, and also dropped out; an accompanying editorial estimates that only 6% of the 599 hospitals in the study reported data for all 11 years.

Second, it’s important to note that all CLABSIs went down: MRSA infections, drug-sensitive staph (MSSA) and other organisms. So something is going on — but it is not MRSA-specific. Optimistic interpretation: Enhanced infection control in hospitals is suppressing all HAIs. Pessimistic interpretation: Enhanced scrutiny, in the states that account for the most additional hospitals, is negatively affecting HAI reporting. Can we distinguish which? Probably not. On the one hand, CLABSIs started trending down in 2001, before the earliest mandatory reporting legislation became effective. On the other hand, the study doesn’t/can’t associate declines in CLABSIs with any specific interventions — so it is not possible to know from this study whether one particular strategy was responsible for this decline.

Third, to put the study focus in context, MRSA accounts for only about 7% of CLABSIs; according to the paper, it is not those infections’ most common causative organism. And CLABSIs do not account for the largest proportion of MRSA HAIs; according to a 2007 paper, they fall third on the list behind nosocomial pneumonia and septicemia.

Fourth, since it is abstracted from a hospitals data base, this study doesn’t address community MRSA infections — and there are some scientists in the family of MRSA researchers who would insist that it is the increasing prevalence of community infection that is the true driver of the MRSA epidemic.

So: Decreased MRSA HAIs, good news. Reasons, unfortunately unclear. Significance, possibly less than the headlines this morning maintain. But whatever it is that those hospitals were doing, let us hope they keep doing it.

The cite is: Burton, DC, Edwards, JR, Horan, TC et al. Methicillin-resistant Staphylococcus aureus Central Line-Associated Bloodstream Infections in US Intensive Care Units, 1997-2007. JAMA. 2009. 301(7): 727-36.
The accompanying editorial is: Climo, MW. Decreasing MRSA Infections: An End Met by Unclear Means. JAMA. 2009. 301(7)772-3.

Maryn

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