Friday, January 21, 2011

Learning to count...

There's an old joke about asking an accountant "what's 2+2?" and the accountant responds "what do you want it to be?"

Unfortunately, CDC has some creative math rules of its own. So for hospital epidemiologists, 1 + x = 1 when it comes to counting central line days. That is, for patients who have more than one central line, only one line can be counted per day for the denominator in calculation of central line associated bloodstream infection (CLABSI) rates. It's as if only one of the three central lines in the acutely ill ICU patient poses a risk to the patient. Magically, the other two are immune.

In the February issue of Infection Control and Hospital Epidemiology, there is a study by the Hopkins group that examined the effect of the one-catheter-per-day rule and found that counting only one catheter falsely overestimated their CLABSI rate by 36% in 3 surgical ICUs.

Two years ago, our group presented a very similar study at SHEA done in our medical and surgical trauma ICUs. We found that the CDC rule falsely overestimated our CLABSI rate by 20%.

In the era of mandatory public reporting of HAIs, it's imperative that everything be done to produce the most valid data for consumers. I'm baffled that CDC has been so slow to respond to these issues. The focus seems to be on validating surveillance using the methodology as is, rather than modifying the methodology to make it more valid.


  1. What's the rationale for the status quo? Is it that multiple line line-days are too hard to measure? That the comparative rates will be the same anyway, since the ratio of multiple-line line-days to single-line line-days will be about the same for everyone? Something else?

  2. I don't know. It's a rule that is probably 30 years old.