Risk Factors for Invasive MRSA Infection in MRSA-Colonized Patients

A recent study published online in the American Journal of Infection Control has characterized risk factors for development of active methicillin-resistant Staphylococcus aureus (MRSA) infection among patients who are colonized with the bacteria at hospital admission.

“Among patients with MRSA colonization, surgery or dialysis during follow-up, and history of hemiplegia were associated with subsequent MRSA infection,” write Jose Cadena, MD, from the University of Texas Health Science Center at San Antonio, and colleagues.

MRSA is a significant pathogen worldwide, and an important cause of healthcare—associated infections (HAIs), ranging from minor skin and soft tissue infections to severe osteomyelitis and sepsis. Yet, despite recent advances in HAI prevention, MRSA continues to cause significant morbidity, mortality, and economic costs in the United States.

According to the authors, MRSA colonization itself is the most important risk factor for invasive MRSA infection, and they say that about one-third of the US population carries S. aureus in their nares. “[T]herefore, it is very important to be able to define the risk factors for active infection in colonized patients,” they stress. However, it has been unclear which of these patients are most likely to develop active MRSA infections.

With this in mind, Dr. Cadena and colleagues performed a retrospective study to assess the long-term risk of invasive MRSA infection among patients who are colonized by MRSA at the time of hospital admission. They conducted their study at the Audie L. Murphy Division of South Texas Veterans Health Care System, identifying individuals who screened positive for MRSA colonization during inpatient acute care admission, and following them until either they developed MRSA infection or to 18 months after they were discharged from hospital.

Of 284 MRSA-colonized patients included in the study, 71 developed invasive MRSA infections (cases) and 213 did not (controls). MRSA invasive infections most commonly affected the skin and soft tissues, lungs, and urinary tract.

The researchers identified several factors that increased the risk of MRSA infection developing in MRSA-colonized patients. These factors included a history of: diabetes mellitus with end organ damage (26% vs 14% [cases vs controls]; P = .02), hemiplegia (9% vs 2%; P = .01), chronic kidney disease (33% vs 20%; P = .03), inpatient admission within 90 days during follow-up (44% vs 29%; P = .03), surgery during follow-up (41% vs 9%; P < .01), or dialysis during follow-up (10% vs 3%; P = .02).

“On multivariable analysis, surgery during follow-up, dialysis during follow-up, and hemiplegia remained significant,” the authors write.

They note that the results of this study confirm that MRSA colonization is associated with surgical site infection, adding that several studies have shown that S. aureus decolonization before surgery is associated with a decreased rate of S. aureus surgical site infections. However, “to our knowledge, we are the first to show that hemiplegia is a risk factor for invasive MRSA infection,” they emphasize. “Knowledge of these risk factors may allow for future targeted interventions to prevent MRSA infections among colonized patients,” the authors conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.