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Background: �Invasive methicillin-resistant Staphylococcus aureus (MRSA) infections� occurring outside of hospitals among individuals with recent healthcare exposures, i.e., healthcare-associated community-onset (HACO), accounted for 58% of all invasive MRSA infections reported to CDC's Active Bacterial Core (ABC) MRSA surveillance system in 2007. �Of these HACO infections, 75% occurred among individuals who were hospitalized in the 12 months prior to infection.
Objective: �To identify risk factors for HACO invasive MRSA infection among recently hospitalized patients.
Methods: �A matched case-control study was performed among patients of two ABCs participating hospitals in Rochester, NY.� A case was defined as a patient with MRSA cultured from a normally sterile body site on ≤ 3rd day of a hospital admission during 2008 or 2009, who had been discharged from the hospital in the prior 100 days.� Controls were matched 1:1 on age group, hospital, and week of admission.� Records of the prior hospitalization were reviewed for comorbid conditions, invasive devices and procedures, antimicrobial exposure, and disposition.� Microbiology records were reviewed for prior non-invasive MRSA infection or colonization in the year prior to infection.� Matched odds ratios were calculated using conditional univariate logistic regression.
Results: �The study includes all 77 cases identified and their matched controls.� Most cases (77%) had MRSA bacteremia; osteomyelitis was the most common infection without documented bacteremia (13%). �Mean age for both groups was 65 years.� Cases were more likely to be male (62% vs. 43%, p<.05). �Cases had higher Charlson comorbidity index (3.3 vs. 2.4, �p<.05) and longer hospital length of stay (median: 8 vs. 3 days, p<.05).� While common in both groups, controls were as likely as cases to have received ICU care, had a surgical or other invasive procedure, received an antimicrobial without MRSA activity, or been discharged to a long-term care facility or with home health services.� Cases were significantly more likely to have had a central venous catheter (CVC) during admission (mOR = 6, 95%CI = 1.8 - 20), been discharged with a CVC (14, 1.8 - 106) (PICC lines being most common [63%]), had a chronic wound (11, 2.6 - 47), or a prior MRSA-positive non-sterile site clinical culture (12, 2.8 - 50).� A MRSA-positive screening culture was not associated with case status (4.5, 0.97 - 21).
Conclusions: � Outpatient invasive MRSA infections among recently hospitalized patients were strongly associated with the presence of a chronic wound, history of a prior non-invasive clinical culture growing MRSA, and discharge with a CVC. �Studies of post-discharge invasive MRSA infection prevention should take these factors into account.