Post-Discharge Methicillin-Resistant Staphylococcus aureus Infections: Epidemiology and Potential Approaches to Control

Post-Discharge MRSA Colonization and Infection

Hospital-associated MRSA infection is reportable in many jurisdictions, but post-discharge MRSA infection is not a specific reportable condition, limiting the available surveillance data. Avery et al [15] studied ICD-9 code data for all hospitals in Orange County, California, and found that 23.5/10,000 hospital admissions were associated with a post-discharge MRSA infection. This nearly tripled the incidence of health care–associated MRSA infection, compared to surveillance that included only hospital-onset cases. Future research should refine these observations, as ICD-9 code data correlate imperfectly with chart reviews and have not yet been well validated for MRSA research.

The CDC estimated that in 2011 there were 48,353 CO-HCA MRSA infections resulting in 10,934 deaths. This estimate is derived from study of the Active Bacterial Core surveillance sample [8]. In that sample, 79% of CO-HCA MRSA infections occurred in patients hospitalized within the last year. Thus, we can estimate that there were 34,249 post-discharge MRSA infections resulting in 8638 deaths in the United States in 2011.

MRSA colonization is the antecedent to infection in the majority of cases [22]. Thus we can assess the health care burden of post-discharge MRSA by analyzing colonization as well as infection. Furthermore, the risk of MRSA colonization of household members can be addressed. Lucet et al evaluated hospital inpatients preparing for discharge to a home health care setting, and found that 12.7% of them were colonized with MRSA at the time of discharge, and 45% of them remained colonized for more than a year [23]. Patients who regained independence in activities of daily living were more likely to become free of MRSA colonization. The study provided no data on the risk of MRSA infection in the colonized patients. 19.1% of household contacts became colonized with MRSA, demonstrating that the burden of MRSA extends beyond the index patient. None of the colonized household contacts developed MRSA infection during the study period.

Risk Factors for Post-Discharge MRSA

Case control studies of patients with post-discharge invasive MRSA have shed light on risk factors for infection. While many risk factors are not modifiable, these studies may provide a road map to development of prevention strategies for the post-discharge setting. A study of hospitals in New York that participated in the Active Bacterial Core surveillance system identified a statistically significant increased risk of MRSA invasive infection among patients with several factors associated with physical disability, including a physical therapy evaluation, dependent ambulatory status, duration of hospitalization > 5 days, and discharge to a long-term care facility. Additional risk factors identified in the bivariate analysis were presence of a central venous catheter, hemodialysis, systemic corticosteroids, and receiving anti-MRSA antimicrobial agents. When subjected to multivariate analysis, however, the most significant and potent risk factor was a previous positive MRSA clinical culture (matched odds ratio 23, P < 0.001). Other significant risk factors in the multivariate analysis were hemodialysis, presence of a central venous catheter in the outpatient setting, and a visit to the emergency department [24]. A second, larger, multistate study also based on data from the Active Bacterial Core surveillance system showed that 5 risk factors were significantly associated with post-discharge invasive MRSA infection: (1) MRSA colonization, (2) a central venous catheter (CVC) present at discharge, (3) presence of a non-CVC invasive device, (4) a chronic wound in the post-discharge period, and (5) discharge to a nursing home. MRSA colonization was associated with a 7.7-fold increased odds of invasive MRSA infection, a much greater increase than any of the other risk factors [25]. Based on these results, strategies to consider include enhanced infection measures for prevention of incident MRSA colonization in the inpatient setting, decolonization therapy for those who become colonized, removal of non-essential medical devices, including central venous catheters, excellent nursing care for essential devices and wounds, hand hygiene, environmental cleaning, and antimicrobial stewardship.