Why all the letters? STAR*ICU and VA studies agree!

Remember that April 2011 New England Journal of Medicine issue with results from two seemingly contradictory studies on MRSA control? Here was our take on both the VA and STAR*ICU studies, written the same week the studies were released. Apparently, some people chose to dust off their typewriters and comment the old-fashioned way. Those letters, and the authors’ responses, are now published. Aside from the last two letters, which make a good point about a flaw in the denominator of the VA study (the failure to remove patients not at risk for acquisition by virtue of already being colonized), all the letters start from the premise that these two studies have contradictory results.

As Charlie Huskins and his colleagues point out in their letter, this is a flawed premise. They point to Figure 3 of their paper to make this point—allow me to expand, since they were obviously working within some crazy word limit that bloggers are not bound by.

Below you’ll find Figure 3 from the STAR*ICU study, which graphs the number of MRSA and VRE “events” (new colonization or infection) during an extended baseline period and the intervention period, in both control and intervention units:

No differences between control and intervention units, and no significant difference from the baseline rates, right? Hold on a minute!! It really isn’t fair to compare these data to the VA data, since the VA study doesn’t include a concurrent control group and doesn’t include sufficient baseline data with which to perform a proper segmented regression analysis. So now let’s take all of that extraneous stuff out (you know, all that tedious extended baseline data and the control arm data—get rid of it!!!). Now the graph looks like this:

The trend line is mine, and demonstrates that MRSA and VRE events dropped by about a third in the intervention units. Since this measure incorporates both transmission and infection metrics, you’d predict it would land smack in the middle of the VA estimates for reduction in MRSA transmission (17-21% reduction) and infection (62% reduction). And it does!

So please stop claiming that the VA study and the STAR*ICU study don’t agree—they do agree, if you just ignore the baseline and control arm data. And as we’ve already learned, control groups are for losers.