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

Infection Control Programs

Classic infection control programs, developed in the 1960s, focused on infections that presented more than 48 to 72 hours after admission and prior to discharge from hospital. In that era, the average length of hospital stay was 1 week or more, and there was sufficient time for health care–associated infections to become clinically apparent. In recent years, length of stay has progressively shortened [13]. As hospital stays shortened, the risk that an infection caused by a health care–acquired pathogen would be identified after discharge grew. More recent studies have documented that the majority of HO-HCA infections become apparent after the index hospitalization [8,14].

Data from the Active Bacterial Core Surveillance System quantify the burden of CO-HCA MRSA disease at a national level [8,14]. However, it is not readily detected by many hospital infection surveillance programs. Avery et al studied a database constructed with California state mandated reports of MRSA infection and identified cases with MRSA present on admission. They then searched for a previous admission, within 30 days. If a prior admission was identified, the MRSA case was assigned to the hospital that had recently discharged the patient. Using this approach, they found that the incidence of health care–associated MRSA infection increased from 12.2 cases/10,000 admissions when traditional surveillance methods were used to 35.7/10,000 admissions using the revised method of assignment of health care exposure [15]. These data suggest that post-discharge MRSA disease is underappreciated by hospital infection control programs.

Lessons from Hospital-Onset MRSA

The morbidity and mortality associated with MRSA have led to the development of vigorous infection control programs to reduce the risk of health care–associated MRSA infection [16–18]. Vertical infection control strategies, ie, those focused on MRSA specifically, have included active screening for colonization, and nursing colonized patients in contact precautions. Since colonization is the antecedent to infection in most cases, prevention of transmission of MRSA from patient to patient should prevent most infections. There is ample evidence that colonized patients contaminate their immediate environment with MRSA, creating a reservoir of resistant pathogens that can be transmitted to other patients on the hands and clothing of health care workers [19,20]. Quasi-experimental studies of active screening and isolation strategies have shown decreases in MRSA transmission and infection following implementation [18]. The only randomized comparative trial of active screening and isolation versus usual care did not demonstrate benefit, possibly due to delays in lab confirmation of colonization status [21]. Horizontal infection control strategies are applied to all patients, regardless of colonization with resistant pathogens, in an attempt to decrease health care–associated infections with all pathogens. Examples of horizontal strategies are hand hygiene, environmental cleaning, and the prevention bundles for central line–associated bloodstream infection.

The Burden of Community-Onset MRSA

CO-HCA MRSA represents 60% of the burden of invasive MRSA infection [8]. While this category includes cases that have not been hospitalized, eg, patients on hemodialysis, post-discharge MRSA infection accounts for the majority of cases [15]. Recent data indicate that the incidence of HO-HCA MRSA decreased 54.2% between 2005 and 2011 [8]. This decrease in HO-HCA MRSA infection occurred concurrently with widespread implementation of vigorous horizontal infection control measures, such as bundled prevention strategies for central line–associated bloodstream infection and ventilator-associated pneumonia. The decline in CO-HCA MRSA infection has been much less steep, at 27.7%. The majority of the CO-HCA infections are in post-discharge patients. Furthermore, the incidence of CO-HCA MRSA infection may be underestimated [15].