A Novel Approach to Methicillin-resistant Staphylococcus Aureus (MRSA) Screening of Colonized Patients

MRSA Colonization

MRSA, colonization, nucleic acid amplification, chromogenic agar

Methicillin-resistant Staphylococcus aureus (MRSA) is endemic in hospital settings. Colonization with MRSA puts patients at increased risk for invasive infections, and MRSA infections have been associated with high costs and adverse clinic outcomes. Patients can clear MRSA spontaneously. Improved approaches for identifying patients who are no longer colonized are needed; we hypothesize that more sensitive nucleic acid amplification can be used to improve identification of patients who are no longer colonized.

Compared with patients with methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia, patients with MRSA bacteremia remained in the hospital for two more days on average and had a median attributable increment in hospital charges of approximately $7000. MRSA status is a determinant of bed allocation, especially in shared-room settings, which represent the most common organization in the US and globally. Based on guidelines from the Centers for Disease Control and Prevention, once patients are designated as having had a positive MRSA culture (either colonized or from a clinical isolate), they require Contact Precautions. This requirement translates into either cohorting with other patients with similar precautions status (i.e., two patients with MRSA share a room) or placement in a private room in the hospital. Cohorting is not the preferred infection control method, but in shared-room settings, it is the most common scenario, particularly in hospitals with high occupancy. Individuals can clear MRSA colonization spontaneously. In fact, up to 38% of patients with MRSA-positive cultures taken greater than 3 months prior were found to be MRSA-negative during a re-screening program conducted by the Massachusetts General Hospital Infection Control Unit from 2004-2006. Other studies have demonstrated that a majority of patients are likely to clear colonization at various time points from original documentation of MRSA infection or colonization. There is currently no standardized approach or accepted guidelines for addressing screening for clearance of colonization in the growing pool of patients who have previous MRSA colonization/infection. Many organizations do provide guidelines for screening, but these guidelines are not based on rigorous study, have a variety of permutations, and have neither consensus acceptance nor adequate implementation among the medical community. The status quo limits bed availability and delays patient discharge to rehabilitation facilities, adversely affecting quality and efficiency, and resulting in use of additional hospital resources. In addition to problems associated with patient flow for admissions and discharges, precaution status results in additional disruptions of patient care through bed moves to accommodate the use of shared rooms by like patients needing Contact Precautions. A patient's precaution status affects his/her care from admission through discharge. During pre-admission, patients identified as previously having MRSA are affected by bed shortages and delays to admission while in emergency departments. While admitted, under current practices, patients who have in fact cleared MRSA may be cohorted with those who have active infection or persistent colonization, putting them at risk of recolonization and hospital acquired infection (HAI). Finally, patients who are on precautions for MRSA often have delayed discharge to rehabilitation or nursing facilities because of bed constraints similar to those experienced by acute care facilities. We hypothesize that the use of more sensitive Polymerase Chain Reaction (PCR) methods detecting MRSA in nasal swabs can facilitate identification of true negative patients and can reliably do so with a single negative test in a shorter period of time, thereby greatly facilitating the ability to complete testing on a larger proportion of patients.

United States

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