Molecular and clinical characteristics of hospital and community onset methicillin-resistant Staphylococcus aureus strains associated with bloodstream infections.

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are classified epidemiologically as health care-associated hospital onset (HAHO)-, health care-associated community onset (HACO)-, or community-associated (CA)-MRSA. Clinical and molecular differences between HAHO- and HACO-MRSA BSI are not well known. Thus, we evaluated clinical and molecular characteristics of MRSA BSI to determine if distinct features are associated with HAHO- or HACO-MRSA strains. Molecular genotyping and medical record reviews were conducted on 282 MRSA BSI isolates from January 2007 to December 2009. MRSA classifications were 38% HAHO-, 54% HACO-, and 8% CA-MRSA. Comparing patients with HAHO-MRSA to those with HACO-MRSA, HAHO-MRSA patients had significantly higher rates of malignancy, surgery, recent invasive devices, and mortality and longer hospital stays. Patients with HACO-MRSA were more likely to have a history of renal failure, hemodialysis, residence in a long-term-care facility, long-term invasive devices, and higher rate of MRSA relapse. Distinct MRSA molecular strain differences also were seen between HAHO-MRSA (60% staphylococcal cassette chromosome mec type II [SCCmec II], 30% SCCmec III, and 9% SCCmec IV) and HACO-MRSA (47% SCCmec II, 35% SCCmec III, and 16% SCCmec IV) (P < 0.001). In summary, our study reveals significant clinical and molecular differences between patients with HAHO- and HACO-MRSA BSI. In order to decrease rates of MRSA infection, preventive efforts need to be directed toward patients in the community with health care-associated risk factors in addition to inpatient infection control.