Hospital Onset Staphylococcus aureus Bacteremia is a Better Measure than MRSA Bacteremia in Assessing Infection Prevention: Evaluation of 51 US Hospitals

BACKGROUND: Hospital Onset (HO) Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is publicly reported and tied to the Hospital-Acquired Conditions Reduction program. It reflects a surrogate of risk of infection of MRSA invasive disease in the hospital setting, and reported as a standardized infection ratio that adjusts for admission MRSA prevalence, hospital size and medical school affiliation. However, it may not adequately represent all HO S. Aureus bacteremia, which is unaffected by the prevalence of resistance to methicillin. METHODS: We compared the rates of NHSN-defined laboratory ID events for HO methicillin susceptible S. Aureus (MSSA) and MRSA bacteremia in 51 hospitals (small, <100 beds, n = 15; medium, 100–300 beds, n = 15; large, >300 beds, n = 21) from a single health system over a 12-month period abstracting data from one clinical decision support system. We also compared the rates of HO S. Aureus bacteremia based on hospital size. RESULTS: 340 HO S. Aureus bacteremia events (1.22 per 10,000 patient-days) occurred during calendar year 2016 (MSSA n = 218, 64%; MRSA n = 122, 36%). 14/15 small hospitals did not have any HO S. Aureus bacteremia events during the study period. HO MSSA bacteremia rates were 0.58 and 0.77 per 10,000 patient-days for medium size and large-size hospitals respectively (P = 0.094). In contrast, HO MRSA bacteremia rates were 0.71 and 0.47 per 10,000 patient-days for medium size and large-size hospitals respectively (P = 0.045). There was no correlation between HO MSSA and MRSA bacteremia for large and medium size hospitals (Figure). CONCLUSION: By measuring only HO MRSA, a significant portion of patients with increased morbidity and mortality are overlooked. HO S. Aureus bacteremia may provide a better measure to use to evaluate invasive S. Aureus risk in the hospital setting, and would mitigate the MRSA prevalence factor. These findings are important when we evaluate policy related to what is considered a hospital acquired condition. DISCLOSURES: All authors: No reported disclosures.