375. Clinical implication of cefazolin inoculum effect on Methicillin-Susceptible Staphylococcus aureus bacteremia
Session: Poster Abstract Session: MRSA, MSSA, Enterococci
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Background: Some strains of Staphylococcus aureus producing type A or C β-lactamase (Bla) show cefazolin inoculum effect (CIE). Cefazolin is a common antibiotics for methicillin-susceptible S. aureus (MSSA) bacteremia. However, clinical implication of CIE on MSSA bacteremia is obscure.

Methods: A retrospective cohort study was performed in the 3 teaching hospitals. MSSA bacteremic patients treated by cefazolin were included. Cefazolin MICs were measured at a standard inoculum (SI, ~5 x 105 CFU/ml) and a high inoculum (HI, ~5 x 107 CFU/ml). The CIE was defined as ≥ 4-fold increasing in MIC from a SI to a HI. The blaZ gene was amplified and sequenced to identify the type of Bla. Sequence analysis was performed by using the BLAST network service.

Results: Among a total of 113 MSSA isolates, 65 (57.5%) had a CIE. 88 (77.9 %) were positive for blaZ gene; type A, B, C and D were 15 %, 21.2 %, 40.7 % and 0.8 %, respectively. For cefazolin MIC (geometric mean) of the total strains, type A, B, C and D Bla positive strains at HI were 3.90 μg/mL, 18.83 μg/mL, 1.46 μg/mL, 7.65 μg/mL, and 1 μg/mL, respectively. MICs increased to ≥16 μg/mL in 23 (20.4%) strains at HI. Most common site of infection was skin & soft tissue (34.5%) following primary bacteremia (20.4%), catheter-related infections (17.7%), osteomyelitis (15%), pneumonia (8%), arthritis (8%), and endocarditis (3.5%). In the multivariate analysis, endocarditis (aOR, 28.51; 95% CI, 1.04-781.52; P = 0.047) and pneumonia (aOR 9.05; 95% CI, 1.17-69.79; P = 0.035) were significantly associated with treatment failure. The CIE (aOR 2.34; 95% CI, 0.61-8.92; P = 0.215) and the type A Bla were not significantly associated with treatment failure. Among 45 patients with serious infections such as endocarditis, pneumonia and osteomyelitis, the patients infected by the strains with CIE had higher failure rate (47% vs. 25%, P = 0.114) and bacteremia-related mortality rate (12% vs. 0%, P = 0.242) than the strains without CIE although they were not statistically significant.

Conclusion: The CIE might be associated with clinical failure if cefazolin is used for serious MSSA infections. However, the CIE is not significantly implicated in the cefazolin failure of MSSA bacteremia and the severity of infection is more important factor for clinical outcome than the CIE.

Shinwon Lee, MD1, Ki Tae Kwon, MD, PhD1, Hye-In Kim, MD2, Hyun Ha Chang, MD, PhD2, Jong-Myung Lee, MD, PhD2, Pyoeng Gyun Choe, MD3, Wan Beom Park, MD, PhD3, Nam Joong Kim, MD, PhD3, Myoung-Don Oh, MD, PhD3 and Shin-Woo Kim, MD, PhD2, (1)Internal Medicine, Daegu Fatima Hospital, Daegu, South Korea, (2)Internal Medicine, Kyungpook National University Hospital, Daegu, South Korea, (3)Internal Medicine, Seoul National University College of Medicine, Seoul, South Korea

Disclosures:

S. Lee, None

K. T. Kwon, None

H. I. Kim, None

H. H. Chang, None

J. M. Lee, None

P. G. Choe, None

W. B. Park, None

N. J. Kim, None

M. D. Oh, None

S. W. Kim, None

Findings in the abstracts are embargoed until 12:01 a.m. PST, Oct. 2nd with the exception of research findings presented at the IDWeek press conferences.