Conference Coverage

VA study finds high MRSA infection risk among those colonized with the bacterium



– Patients colonized with MRSA are at high risk of MRSA infection both in the predischarge and postdischarge time periods, results from an 8-year Veterans Affairs study showed.

“MRSA colonization is recognized as being a strong predictor of subsequent infection,” Richard E. Nelson, PhD, said at an annual scientific meeting on infectious diseases. “What’s less understood is, are there differences in infection rates among patients who are colonized at different times? And, is there a difference between patients who import colonization with them to a hospital versus those who acquire it during a hospital stay? In addition, infection control efforts mainly focus on the predischarge time period. What about infections that develop post discharge?”

In an effort to investigate these questions, Dr. Nelson of the VA Salt Lake City Healthcare System, and his associates, evaluated more than 1.3 million acute care inpatient admissions to 125 VA hospitals nationwide from January 2008 through December 2015 who had surveillance tests performed for MRSA carriage.

Doctors tend to a patient in a hospital bed. copyright Pixland/Thinkstock

The researchers restricted admissions to individuals with at least 365 days of VA activity prior to admission and categorized them into three groups: no colonization (defined as those who had no positive surveillance tests (n = 1,196,928); importation (defined as those who tested positive for MRSA colonization on admission (n = 95,833); and acquisition (defined as those who did not test positive for MRSA on admission but tested positive on a subsequent surveillance test during their admission (n = 15,146). Next, they captured MRSA infections in these individuals prior to discharge and at 30 and 90 days post discharge. Infections were defined as positive MRSA cultures taken from sterile sites, including blood, catheter site, or bone.

Overall, patients were in their mid-60s, and those who imported MRSA and those who acquired it were more likely to be male, less likely to be married, and more likely to not have health insurance. The acquirers had by far the highest rates of predischarge infections, which peaked in 2010 and declined through 2015,” said Dr. Nelson, who also holds a faculty position in University of Utah’s department of internal medicine, in the division of epidemiology. Specifically, the proportion of predischarge MRSA infections, compared with 30 days post discharge, were 40.4% vs. 59.6%, respectively, in the no colonization group; 63% vs. 37% in the importation group, and 80.8% vs. 19.2% in the acquisition group.

He also reported that the proportion of predischarge MRSA infections, compared with 90 days post discharge, were 20.5% vs. 79.5%, respectively, in the no colonization group; 47.3% vs. 52.7% in the importation group, and 70.5% vs. 29.5% in the acquisition group. The time from acquisition to infection was a mean of 8.7 days in the 30-day analysis and a mean of 22.4 days in the 90-day analysis.

Multivariate logistic regression revealed that the impact of colonization status on infection was highest in the acquisition group, compared with the importation group. Specifically, the odds ratio of developing a MRSA infection among the importation group was 29.22 in the predischarge period, OR 10.87 at post discharge 30 days, and OR 7.64 at post discharge 90 days (P less than .001 for all). Meanwhile, the OR among the acquisition group was 85.19 in the predischarge period, OR 13.01 at post discharge 30 days, and OR 8.26 at post discharge 90 days (P less than .001 for all).

Dr. Nelson acknowledged certain limitations of the study, including the fact that it only identified postdischarge infections that were detected in a VA facility. “This is likely an underestimate of postdischarge infections, because we’re missing the infection that occur in non-VA facilities,” he said at the event, which marked the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society. “Also, patients can be colonized in many different body locations, but the VA protocol is that the surveillance test be done in the nostrils. So we may have misclassified patients who were colonized in a different body location as being uncolonized, when in fact they were colonized.”

The study was funded by a grant from the VA. Dr. Nelson reported having no financial disclosures.

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