Epidemiology of Staphylococcus aureus Bacteremia in a Large tertiary center

Background: Staphylococcus aureus is the leading cause of community-acquired and healthcare-associated bacteremia.

Methods:  Retrospective chart review of patients with S. aureus bacteremia, methicillin resistant (MRSA) and Methicillin sensitive (MSSA), over the last 2 years. Data were gathered on Demographics, Hospital(HO) vs Community onset (CO)), mortality, length of stay, time to clear Blood Cultures, readmissions and comorbidities.

Results: 211 patients enrolled, 57% MRSA. 58% males (MRSA/MSSA=51/72) while females had (MRSA/MSSA=40/48). Caucasian 77% and African American17%. Patients on Cardiology & Nephrology service had a higher incidence with 21%(n=45) & 13%(n=29) respectively. No significant variation was noted in the incidence of bacteremia between summer months and winter months. More than 50%(n=109) of the infections were seen among the 45-74 year age group most commonly between 55-64 year old patients(n=41). CO infections accounted for 67%. 35.3% vs 28.3% was readmitted within 90 days of MSSA and MRSA respectively. Out of these readmissions, 34.4% vs 50% (MSSA vs MRSA) of patients had recent history of bacteremia.  16 % of MSSA population died within 90 days of admission compared to 37 % in MRSA. Average length of stay was 21 days for both MSSA & MRSA. Time needed to clear blood cultures was 5.8 days’ vs 7.55 days (MSSA vs MRSA) respectively. Central line was a possible source in 57%(n=52) vs 60%(n=72) of MSSA vs MRSA bacteremia patients.  Of these, 65 % of MSSA (34/52) and MRSA (47/72) had positive central line tip cultures most commonly among those with PICC and Ashsplit lines. Obese patients with BMI > 30 seemed to have higher incidence of infections (42%) compared to patients with normal BMI(25.6%). The top five comorbidities remained the same for both MSSA and MRSA patient population consisting of Hypertension, Diabetes, Chronic kidney disease/End stage renal disease, Hyperlipidemia, Coronary artery disease/Peripheral vascular disease.

Conclusion: Cardiac and Nephrology patients at higher risk of S. aureus bacteremia. The rate of readmission in MSSA bacteremia is comparable to that of MRSA. Mortality within 90 days higher and time needed to clear blood cultures longer, in patients with MRSA bacteremia.