Mapping C. dfficile hospital acquisition: short-stay diagnostic areas are important!

Recent genomic studies have concluded that hospital-acquired acquisition of C. difficile is rare, suggesting that acquisition of C. difficile outside of hospitals followed by hospital-onset disease is the most common explanation for C. difficile infection. These studies hinge on an assumption that in-hospital patient contact occurs due to shared or recent stay on the same hospital ward. A short publication in JAMA Internal Medicine eloquently challenges this assumption, suggesting that hospital contact that we would usually assume to be casual and not a risk for acquisition of hospital pathogens (e.g. short-stay diagnostic areas such as ultrasound and endoscopy) can be an important source of acquisition.

The study was performed over two years in a hospital in California. The study evaluated whether using any clinical area (be it an inpatient ward or short-stay diagnostic or treatment area) within 24 hours of a patient with C. difficile diagnosed at any point during the hospital stay was a risk factor for developing C. difficile infection in the 60 days after exposure. A patient-level logistic regression model was run to control for other variables including patient age, gender, length of hospital stay, proton pump inhibitor use, prior hospitalisation, and inflammatory bowel disease. Clearly, antibiotic exposure is a big missing variable here…

A whopping 90,000 patients were included, with more than 400,000 individual stops in clinical areas. The key finding is that contact with the CT scanner in the ED in the 24 hours after a known patient with C. difficile was significantly associated with a 3-fold increase in the changes of a patient developing C. difficile infection in the 60 days after the exposure; this remained significant after adjustment for the other variables (OR, 2.7; 95% CI, 1.3-5.7) (see the Figure below).

Figure 1: Mapping the rate of developing C. difficile in the 60 days following exposure to these areas; this figure has grown on me. I thought it was over-complex at first, but it does a good job of getting across the volume of patients exposed to C. difficile in these areas and the rate of C. difficile infection. 

Some point for further thought / discussion:

  • We have to use ‘ difficile infection’ in its loosest (!) sense for this study. This is about lab specimens positive for C. difficile, which isn’t the same as infection. Related to this, there was no need for patients to have diarrhoea to qualify as creating an exposure – they could have resolved from them symptoms months ago. A good sensitivity analysis / idea for further study is restricting the exposure to patients with symptomatic infection (but appreciate this would damage power).
  • Antibiotic exposure isn’t included as a variable in the regression model, which is a clear omission (presumably due to lack of this information for every patient in the hospital over two years, which I suppose is forgivable!).
  • It is not immediately clear how this study helps to clarify the source of difficile infection. It looks like the cases associated with short-stays in diagnostic areas accounts for a relatively small proportion of the overall number of cases.
  • The rate of difficile seems really rather high at 13 cases per 1,000 patients – I’d expect this to be approach 10-fold less than that in a UK setting.

Overall this article is thought provoking: how long does it take to acquire C. difficile? Should we think more about short-stays in non-inpatient-ward settings (like imaging and diagnostic areas) in mapping C. difficile spread throughout a hospital? Can we be certain in the conclusions of studies that suggest a relatively small proportion of C. difficile is hospital acquired when they don’t account for possible transmission in these areas?

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