Trends in Staphylococcus aureus (SA) Isolation in 28 US Hospitals, 2009-2013
Methods: We collected SA isolates from July-December in 2009, 2011 and 2013 from a geographically representative sample of US hospitals. 28 centers participated in all 3 surveys, each submitting up to 100 consecutive, unique (1 isolate/patient) clinically-significant SA, with demographic information, during each survey. Susceptibility testing was performed using CLSI methods and mecA PCR. Pulsed field gel electrophoresis (PFGE), spa and SCCmec typing, and pvl detection were performed on all MRSA. We defined as hospital-onset (HO) those SA from cultures obtained >48 h after admission.
Results: A total of 8377 SA isolates were collected (2009:2828, 2011:2767, 2013: 2782). Age distribution of pts was < 5 (6%), 6-20 (10%), 21-64 (59%), and > 65 years (23%), and 55% were male. The most common specimen source was wound/abscess (52%), followed by bloodstream (25%). The % MRSA decreased over time, from 53% of isolates mecA + in 2009-2011 to 46% in 2013. Only 15% of SA were HO: among MRSA, the % that were HO decreased from 15-16% in 2009-2011 to 12% in 2013. HO-MRSA accounted for only 5% of all SA clinical isolates in 2013. The USA300 MRSA PFGE type predominated in all three surveys, and by 2013 a single spa type (t008) accounted for 54% of all MRSA, followed by t002 (17.2%), with no other spa type accounting for more than 2% of MRSA. High level mupirocin resistance increased among SA/MRSA from 1.8/2.2% in 2009 to 2.6/3.9% in 2013.
Conclusion: Consistent with reports of declining HO-MRSA infection rates, our microbiology lab-based surveillance reveals that a decreasing proportion of all SA clinical isolates are MRSA or hospital-onset. Rates of resistance to mupirocin, an agent used often in HO-MRSA prevention programs, are rising. Strategies to prevent SA infections beyond HO-MRSA will be needed to substantially impact the burden of SA disease.
D. J. Diekema,
Forest Labs: Grant Investigator, Research grant
L. Boyken, None
K. Heilmann, None
F. Riahi, None
S. Tendolkar, None
G. Doern, None