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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.