When is an outbreak an outbreak? Using literature and discharge data to define Clostridioides difficile incidence changes referred to as outbreaks

A clinically noticeable increase in Clostridioides difficile infections (CDI) in excess of expectations (i.e. outbreak) lacks a common definition. Understanding what magnitude of CDI incidence growth constitutes an outbreak from the hospital perspective is valuable for retrospective analyses. This study identified CDI incidence metrics reported as outbreaks in the literature and compared these with Healthcare Cost and Utilization Project (HCUP) discharge data. Publications reported a median 4.1x incidence change between outbreak periods and reference periods (N=26, minimum 2x incidence). However, this magnitude change in monthly incidence appeared once in HCUP data (20 hospitals, 2012-2014). Hence, the literature may present examples of extreme outbreaks.