Which infection had a standardized infection ratio (SIR) less than 1 in the dataset?

• A. Surgical site infections (SSIs)
• B. Catheter-associated urinary tract infections (CAUTIs)
• C. Central line-associated bloodstream infections (CLABSIs)
• D. Laboratory identified C. difficile infections (CDIs)

Answer: (D)

The main idea is understanding what a standardized infection ratio (SIR) tells us. SIR compares what was observed to what was expected after adjusting for risk. An SIR below 1 means fewer infections occurred than the model predicted, indicating better-than-expected performance for that infection type in the dataset. In this case, laboratory-identified C. difficile infections show an SIR under 1, so the observed number was lower than predicted by the risk-adjusted baseline. This can reflect effective prevention efforts, antibiotic stewardship, or differences in how these infections are identified and reported. The other infection types—surgical site infections, catheter-associated urinary tract infections, and central line-associated bloodstream infections—had SIRs that were at or above 1 in the dataset, meaning observed cases were not fewer than expected.