Methicillin-resistant Staphylococcus aureus (MRSA) nasal screening could be helpful in confirming the absence of MRSA pneumonia in critically ill children and adults, according to new data from two separate studies.
In the first study, presented at the ACCP 2022 Global Conference on Clinical Pharmacy (poster Mon PM-72), investigators wanted to compare the effectiveness of MRSA nasal screening in predicting MRSA infections in patients in the ICUs and on the general wards. “The faster that we can use these to guide our antimicrobial therapy and get patients off of anti-MRSA therapies including vancomycin and linezolid, the more we can reserve those for actual MRSA infections,” said poster presenter Stormmy Boettcher, a fourth-year student at the University of Arizona College of Pharmacy.
Researchers from Banner University Medical Center in Phoenix directed the work, a retrospective chart review of patients aged 18 years and older who had MRSA nasal screenings within 48 hours of collection of a respiratory and/or blood culture, and initiation of either linezolid or vancomycin as an anti-MRSA agent. They excluded patients with cystic fibrosis. Physicians and pharmacists could order MRSA nasal screenings for admitted patients at their discretion, to be collected by bedside nurses. Swabs were batched twice daily, with an estimated 24-hour incubation.
There were 5,106 patients (2,515 in the ICUs and 2,591 on the general wards) included in the study. ICU patients had a median age of 60, and 63% were male. Looking at comorbidities, 48.7% had diabetes, 14.2% had asthma, 36.6% had chronic obstructive pulmonary disease (COPD), 25.8% had hepatic dysfunction and 36.5% had chronic kidney disease (CKD). Patients on the general wards were somewhat similar, with a median age of 64 and 56.6% were male. Fifty-two percent of general ward patients had diabetes, 17.7% asthma, 43.5% COPD, 27.4% hepatic dysfunction and 39.9% CKD.
Data Suggest Screening Can Guide De-escalation
Negative predictive value (NPV) of the MRSA nares for suspected pneumonia was not significantly different between the ICU and general ward patient populations (98.3% and 97.6%, respectively; P=0.41), demonstrating in each set of patients that the screen could indicate patients who did not have pneumonia and therefore could support the de-escalation of anti-MRSA therapy.
The MRSA nares screening tool also had a high NPV for suspected bacteremia in the ICU and general ward groups (99.8% and 99.7%, respectively; P=0.56). However, there were not enough patients with bacteremia to provide statistical power for any association. The overall MRSA prevalence among patients with suspected pneumonia was 5.6%, and only 0.7% for those with suspected bacteremia. Among patients with a negative MRSA test result, the total duration of anti-MRSA therapy across institutions in the ICU group was four days but three days on the general wards.
Providers on the general ward are “well versed with the use of nasal screening” and rely on it to guide therapy, Ms. Boettcher said. “But in the ICU, we still have this hesitation of using it because we don’t want to take someone off of an anti-MRSA therapy and then have a culture result.”
There is room for education in the ICU about how well the nasal screening should be used, Ms. Boettcher said: “With respiratory cultures, the ICU attendings and our medical colleagues may need some more education about using this and promoting antimicrobial stewardship in general.”
The study adds to the growing body of evidence to support the use of MRSA nasal screening results to aid in therapy decisions, according to Ashlee Hamel, PharmD, MHA, BCPS, the system manager for pharmacy clinical programs at Sentara Healthcare, in Norfolk, Va.
Groups such as the Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America have guidelines outlining the appropriate use of MRSA nasal swabs for various indications, Dr. Hamel noted. Quick discontinuation of linezolid and vancomycin as empirical therapy can reduce the potential for kidney injury, drug–drug interactions, adverse reactions, potential resistance and healthcare costs, she said.
Sentara Healthcare, with 12 acute care hospitals across Virginia and North Carolina, has used MRSA nasal screening to assist in rapid antibiotic de-escalation in patients with pneumonia for several years. Their protocol allows pharmacists to order nasal cultures and use the results to discontinue antibiotics, if indicated. They hope to expand to additional indications in the near future, Dr. Hamel said.
Sparing Vancomycin in Children
In the second study, data suggest that screening with a polymerase chain reaction (PCR) MRSA nasal swab can be useful for guiding antibiotic therapy of invasive MRSA infection in severely ill children. In the study, the PCR screen had a very high NPV and proved to be particularly useful in identifying inappropriate vancomycin use.
The researchers conducted a retrospective cohort study in a 44-bed pediatric ICU (Crit Care Med 2023;51[1]:3). It was standard for all ICU admissions to be screened with MRSA PCR. They tested the nasal swab samples using the Xpert MRSA (GeneXpert, Cepheid) system. Children were included in the study if the researchers saw signs or symptoms of infection.
From 7,696 pediatric patient encounters, the researchers identified 29 children (median age, 5 years) with an invasive MRSA infection (0.9%). The incidence of invasive MRSA was 1.6 per 1,000 patient-days, and 69% of isolated MRSA cultures were from samples taken from the respiratory tract, according to the researchers.
“We found in our study that although only 0.9% of the patients had culture-proven invasive MRSA infection, nearly 45% of patients received at least one dose of vancomycin with an average length of treatment of three days for those receiving vancomycin,” said Lexi Crawford, MD, a pediatric critical care fellow in the Division of Critical Care Medicine at the Children’s National Hospital, in Washington, D.C., who presented the data at the 2023 Critical Care Congress, held in San Francisco.
Although invasive MRSA can lead to significant morbidity and mortality if not recognized and treated promptly, “unnecessary prolonged use of intravenous vancomycin results in increased patient risk of iatrogenic acute kidney injury, adverse drug reactions, development of resistant organisms and subjection to frequent blood draws for drug level and renal function monitoring,” Dr. Crawford said.
She added the results may not be generalizable to centers with significantly higher prevalence of MRSA or in individual patients with risks that convey a high pretest probability of MRSA infection.
“Invasive MRSA infection is rare in pediatrics; however, determination of which patients warrant empiric coverage with a MRSA-active agent continues to represent a clinical dilemma often leading to unnecessary patient exposure to vancomycin,” Dr. Crawford said. “Therefore, a test like the MRSA nasal swab PCR—which we have shown has a high negative-predictive value that could be used to help augment current infectious evaluation and support clinical decision making when selecting empiric antibiotic regimens—will hopefully lead to a reduction in unnecessary or prolonged use of vancomycin.”
The sources reported no relevant financial disclosures.
This article is from the June 2023 print issue.