Impact of Prior Hospitalization on Methicillin-Resistant Staphylococcus aureus Bloodstream Infections over Three Decades Open Access

Robichaux, Chad (2014)

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The epidemiology of Staphylococcus aureus bloodstream infections has changed in recent decades, with an increase in the proportion due to methicillin-resistant S. aureus (MRSA) occurring outside of a hospital setting. This change is due in part to shifting of healthcare to the outpatient setting and the emergence of community-onset MRSA as a cause of skin and soft-tissue infections. Using all initial S. aureus positive blood cultures at one hospital during the first four years of 3 decades (1990-1993, 2000-2003, and 2010-2013), we hypothesized that prior hospital admission within one month would be associated with a greater risk for methicillin resistance among those with S. aureus bloodstream infection. The number of S. aureus bloodstream infections increased from 432 (1990-1993) to 637 (2000-2003), then decreased to 432 in the most recent study period (2010-2013). The decrease in the number of infections between the middle and last time periods was largely driven by a 50% decrease in infections occurring in the hospital. Similarly, the percent MRSA increased from 25% (1990-1993) to 52% (2000-2003) then declined to 47% in the most recent study period (2010-2013). The proportion with community-onset infections, end-stage renal disease, and HIV increased over time. Mortality was higher among those patients with MRSA in all study periods. The final model based on backward selection included patient age, whether the infection occurred in a community setting, HIV diagnosis, and the time period in which the culture was collected. Analysis showed no significant association between prior admission in the last month and methicillin resistance among these bloodstream infections (P= 0.35). While we could not demonstrate that prior hospitalization was a risk for developing MRSA bloodstream infections, the drop in hospital-onset S. aureus bloodstream infections in the last study period was striking. S. aureus bloodstream infections are still a problem, but prevention efforts may be decreasing the observed incidence. Future directions may include expanding hospital-based efforts to the outpatient setting.

Table of Contents

Introduction 1 Background 1 Methods 2 Results 6 Discussion 11 Table 1a 15 Table 1b 17 Table 2 19 Table 3 21 Table 4 23 Table 5 25 Table 6 27 Table 7 30 Table 8 31 Table 9 32 References 33 Appendix A: SAS Code 35

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