Post-Discharge Methicillin-Resistant Staphylococcus aureus Infections: Epidemiology and Potential Approaches to Control
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.
Development of Strategies to Decrease Post-Discharge MRSA
While the epidemiology of post-discharge health care–associated MRSA infections has become a topic of interest to researchers, approaches to control are in their infancy. Few of the approaches have been subjected to rigorous study in the post-discharge environment. Nevertheless, some low risk, common sense strategies may be considered. Furthermore, an outline of research objectives may be constructed.
Prevention of Colonization in the Inpatient Setting
Robust infection control measures must be implemented in inpatient settings to prevent incident MRSA colonization [16,17]. Key recommendations include surveillance and monitoring of MRSA infections, adherence to standard hand hygiene guidance, environmental cleanliness, and use of dedicated equipment for patients who are colonized or infected with MRSA. Active screening for asymptomatic MRSA carriage and isolation of carriers may be implemented if routine measures are not successful.
Decolonization
Despite the best infection control programs, some patients will be colonized with MRSA at the time of hospital discharge. As detailed above, MRSA colonization is a potent risk factor for infection in the post-discharge setting, as well as in hospital inpatients [22]. A logical approach to this would be to attempt to eradicate colonization. There are several strategies for decolonization therapy, which may be used alone or in combination, including nasal mupirocin, nasal povidone-iodine, systemic antistaphylococcal drugs alone or in combination with oral rifampin, chlorhexidine bathing, or bleach baths [26–29].
A preliminary step in approaching the idea of post-discharge decolonization therapy is to show that patients can be successfully decolonized. With those data in hand, randomized trials seeking to demonstrate a decrease in invasive MRSA infections can be planned. Decolonization using nasal mupirocin has an initial success rate of 60% to 100% in a variety of patient populations [30–35]. Poor adherence to the decolonization protocol may limit success in the outpatient setting. Patients are more likely to resolve their MRSA colonization spontaneously when they regain their general health and independence in activities of daily living [23]. Colonization of other household members may provide a reservoir of MRSA leading to recolonization of the index case. Treatment of the household members may be offered, to provide more durable maintenance of the decolonized state [35]. When chronically ill patients who have been decolonized are followed longitudinally, up to 39% become colonized again, most often with the same strain [30,31]. Attempts to maintain a MRSA-free state in nursing home residents using prolonged mupirocin therapy resulted in emergence of mupirocin resistance [31]. Thus decolonization can be achieved, but is difficult to maintain, especially in debilitated, chronically ill patients. Mupirocin resistance can occur, limiting success of decolonization therapies.
Successful decolonization has been proven to reduce the risk of MRSA infection in the perioperative, dialysis, and intensive care unit settings [33,36–38]. In dialysis patients the risk of S. aureus bloodstream infection, including MRSA, can be reduced 59% with the use of mupirocin decolonization of the nares, with or without treatment of dialysis access exit sites [37]. A placebo-controlled trial demonstrated that decolonization of the nares with mupirocin reduced surgical site infections with S. aureus. All S. aureus isolates in the study were methicillin-susceptible. A second randomized controlled trial of nasal mupirocin did not achieve a statistically significant decrease in S. aureus surgical site infections, but it showed that mupirocin decolonization therapy decreased nosocomial S. aureus infections among nasal carriers [33]. 99.2% of isolates in that study et al were methicillin-susceptible. Quasi-experimental studies have shown similar benefits for surgical patients who are colonized with MRSA [39–41]. A more recent randomized trial, in ICU patients, demonstrated decreased incidence of invasive infection in patients treated with nasal mupirocin and chlorhexidine baths [38]. The common themeof these studies is that they enrolled patients who had a short-term condition, eg, surgery or critical illness, placing them at high risk for invasive MRSA infection. This maximizes the potential benefit of decolonization and minimizes the risk of emergence of resistance. Furthermore, adherence to decolonization protocols is likely to be high in the perioperative and ICU settings. To extrapolate the ICU and perioperative data to the post-discharge setting would be imprudent.
In summary, decolonization may be a useful strategy to reduce invasive MRSA infection in post-discharge patients, but more data are needed for most patient populations. The evidence for decolonization therapy is strongest for dialysis patients, in whom implementation of routine decolonization of MRSA colonized nares is a useful intervention [37]. There are not yet clinical trials of decolonization therapy in patients at time of hospital discharge showing a reduction in invasive MRSA infection. Decolonization strategies have important drawbacks, including emergence of resistance to mupirocin, chlorhexidine, and systemic agents. Furthermore, there is a risk of hypersensitivity reactions, Clostridium difficile infection, and potential for negative impacts onthe normal microbiome. The potential for lesser efficacy in a chronically ill outpatient population must also be considered in the post-discharge setting. Randomized controlled trials with invasive infection outcomes should be performed prior to implementing routine decolonization therapy of hospital discharge patients.
Care of Invasive Devices
Discharge with a central venous catheter was associated with a 2.16-fold increased risk of invasive MRSA infection; other invasive devices were associated with a 3.03-fold increased risk [25]. Clinicians must carefully assess patients nearing discharge for any opportunity to remove invasive devices. Idle devices have been reported in inpatient settings [42] and could occur in other settings. Antimicrobial therapy is a common indication for an outpatient central venous catheter and can also be associated with increased risk of invasive MRSA infection [25,43]. Duration and route of administration of antimicrobial agents should be carefully considered, with an eye to switching to oral therapy whenever possible. When a central venous catheter must be utilized, it should be maintained as carefully as in the inpatient setting. Tools for reducing risk of catheter-associated bloodstream infection include keeping the site dry, scrubbing the hub whenever accessing the catheter, aseptic techniques for dressing changes, and chlorhexidine sponges at the insertion site [44,45]. Reporting of central line–associated bloodstream infection rates by home care agencies is an important quality measure.
