MRSA nasal swabs could determine treatment decisions before culture results are available
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A negative MRSA nasal swab could help clinicians determine whether to withhold or discontinue MRSA treatment while wound or tissue culture results are pending, according to results from a single-center study.
“After the [Veterans Administration (VA)] mandated using MRSA nasal screening by PCR to reduce health care-associated MRSA infections, our VA researchers and infection control doctors wanted to see if there was a concordance between the nasal swab and the subsequent wound and tissue culture,” Anna D. Montgomery, MPH, a health research specialist at Fargo Veterans’ Affairs Health Care System, told Healio. “We thought that the nasal screening could also be a helpful tool for the de-escalation of antibiotic therapy to treat infections.”
Montgomery and colleagues performed a retrospective study that included inpatients who had undergone nasal screening for MRSA and a culture taken from a wound or tissue site within 30 days of admission at a VA hospital to evaluate the potential correlation between nasal screening and wound and tissue site cultures.
Overall, 337 patients underwent nasal screening and wound culture and 211 underwent nasal screening and wound and tissue cultures, the researchers said.
Study data demonstrated that the prevalence of MRSA nasal colonization was 14.2% for wound samples and 15.2% for tissue samples. The sensitivities of nasal screening for detecting MRSA were 64.6% for wound cultures and 65.5% for tissue cultures, and the specificities were 86.2% and 88.8%, respectively. Additionally, researchers found that positive predictive values were 43.7% and 51.2% for wound and tissue cultures, respectively, whereas the negative predictive values (NPVs) were higher at 93.6% and 93.5%, respectively.
Montgomery explained that because of the high NPVs, there is a reasonably high probability that the subsequent wound and tissue cultures will also be negative.
“In combining our study’s finding of high NPVs with an appreciable difference in turnaround times between the nasal swab and the culture in detecting MRSA — approximately 70 minutes for nose swab vs. 24 to 48 hours for wound/tissue culture — clinicians can avoid empirical use of MRSA-targeting agents 1 to 2 days before the final culture results are available,” Montgomery said. “This is an important message in an age of growing antibiotic resistance.”
Among the study’s limitations, the researchers noted that it was a small retrospective review conducted at a single facility.
“However,” they wrote, “our findings suggest a strategy for antimicrobial stewardship, and they add to a limited body of research related to MRSA nasal tests and wound and tissue cultures. To confirm our findings in this area, larger prospective studies in different populations are warranted.”
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