What about the denominator?

Now watch this very short video clip on the importance of choosing an appropriate denominator.

So far we have considered the way to measure the volume of antibiotic use, but that may only be part of the story. It is always helpful to review the raw DDD data to get an indication of whether it is changing over time.

Changes in patient census in the hospital may account for some of any differences observed. A denominator will be needed to enable the measurement of use over time and between hospitals become meaningful. Normalising antibiotic use and presenting it as a rate will help account for fluctuations in hospital activity such as the number of patients in hospital and their length of stay.

So what are the options?

One of the most commonly used denominators in hospital stewardship programmes is the number of patient days or occupied bed days. This requires information on bed utilisation.

The landmark guidance on antimicrobial stewardship by the Infectious Disease Society of America and Society for Healthcare Epidemiology of America recommends DDD/1000 patient days as a metric for hospital based antimicrobial stewardship programmes.

As you consider denominators ask yourself if you can access this type of hospital activity data for your own hospital.