Safety and Quality > Our Work > Healthcare-Associated Infection Prevention Program > National HAI Surveillance > National definition and calculation of Hospital identified Clostridium difficile infection

Case definition – Hospital identified C. difficile infection

Clostridium difficile infection (CDI) case is defined as a case of diarrhoea (that is, an unformed stool that takes the shape of the container) that meets the following criteria:

  • the stool sample yields a positive result in a laboratory assay for C. difficile infection toxin A and/or B, or
  • a toxin-producing C. difficile organism is detected in the stool sample by culture or other means.

A hospital identified CDI case is:

  • a case diagnosed in a patient attending an acute care facility (that is, it includes positive specimens obtained from admitted patients and those attending the Emergency Department, and outpatient departments).


  • Cases where a known previous positive test has been obtained within the last 8 weeks (that is, only include cases once in an 8 week period).
  • Patients less than 2 years old.

Note: An additional positive test obtained from a specimen collected from the same patient more than 8 weeks since the last positive test is regarded as a new case.

Calculation of CDI rates

The following primary information will be used to calculate the rates of C. difficile infection (CDI) in each Australian healthcare facility with acute inpatient beds:

The rates will be calculated monthly for each healthcare facility as follows:

Numerator: Patient episodes of hospital identified CDI (total hospital CDI cases) x 10,000
Denominator: Number of patient days