The Clinical Utility of MRSA Nasal Surveillance Swabs in Ruling-Out MRSA Infections in Children

Utility of Methicillin-Resistant Staphylococcus aureus Nasal PCR Testing in Pediatric Patients With Suspected Respiratory Infections

Observational studies in adults suggest nasal methicillin-resistant Staphylococcus aureus (MRSA) swabs have a high negative predictive value (NPV) for ruling out MRSA pneumonia, however, pediatric data are limited. This retrospective study of 505 pediatric patients found a 99.8% NPV among children with suspected respiratory infections.

Assessing the Concordance of MRSA Carriage Screening With MRSA Infections

OBJECTIVES

This study focused on children with confirmed methicillin-resistant Staphylococcus aureus (MRSA) infections to determine MRSA screening utility in guiding empirical anti-MRSA treatment of children without history of MRSA infection. We examined the concordance of screens to assess differences by infection type and used statistical analysis to determine significant contributors to concordance.

METHODS

Pediatric hospital patients admitted from 2002 through 2022 were included. Subjects had MRSA infections subsequent to MRSA surveillance screens performed the preceding year. Statistical analysis identified associations between MRSA screens and infections. Number needed to treat analysis calculated the utility of rescreening.

RESULTS

Among 246 subjects, 39.0% had concordant screens; 151 (61.4%) screens were obtained in the 2 weeks preceding infection. Sensitivity for bacteremia was 50.0% (n = 42), for endotracheal/respiratory 44.4% (n = 81), and 29.4% (n = 102) for skin and soft-tissue infection. For children aged younger than 6 months, sensitivity was 35.9% (n = 78). Multivariable analysis significantly associated days since screening with decreasing likelihood of concordance. Regression modeled the probability of concordance to drop below 50.0% for all infections after 4 days, after 6 days for bacteremia specifically, and 12 days for endotracheal/respiratory infections.

CONCLUSIONS

The concordance of screens was far lower than negative predictive values found previously; earlier studies were possibly impacted by low prevalence and exclusion of children at high risk to inform high negative predictive values. We suggest that negative MRSA screens should not invalidate reasonable suspicion for MRSA infection in patients with high pretest probabilities.

Predictive Value of Methicillin-Resistant Staphylococcus aureus Nasal Swab PCR Assay for MRSA Infection in Critically Ill Pediatric Patients

BACKGROUND

Critically ill pediatric patients are frequently initiated methicillin-resistant Staphylococcus aureus (MRSA) active antibiotics during infection evaluation even though MRSA infections are rare in many patient populations. The MRSA nasal swab polymerase chain reaction assay (MRSA-NS-PCR) is a test that has been shown to have a high negative predictive value (NPV) for MRSA infection in adults. This study evaluated the diagnostic test characteristics of the MRSA-NS-PCR in predicting the presence of MRSA infection in critically ill pediatric patients.

STUDY DESIGN

A retrospective cohort study was performed in a 44-bed pediatric intensive care unit (PICU) between 2013 and 2017. 3860 pediatric patients (54% male, median age 4 years [IQR 1-11 years]) admitted to the PICU who met pediatric systemic inflammatory response syndrome (pSIRS) criteria, were screened with a MRSA-NS-PCR, and had cultures obtained within seven days of MRSA-NS-PCR collection were included. Predictive values and post-test probabilities of the MRSA-NS-PCR for MRSA infection were calculated.

RESULTS

MRSA-NS-PCR was positive in 8.6% of patients. MRSA infection was identified in 40 patients, equaling an incidence rate of 2 per 1000 patient days. The MRSA-NS-PCR demonstrated a positive predictive value (PPV) of 9.7%, a NPV of 99.8%, and a post-test probability for a negative test of 0.2% for MRSA infection.

CONCLUSIONS

The MRSA-NS-PCR has a poor PPV but a high NPV for MRSA infection in PICU patients when the incidence of MRSA infection is low. Creation of protocols to guide antimicrobial selection based on MRSA-NS-PCR results may lead to improved antimicrobial stewardship and significant risk reduction.

Pediatric Utilization of Methicillin-resistant Staphylococcus aureus Nasal Swabs for Antimicrobial Stewardship

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) can cause serious infections and empiric treatment regimens in children frequently include an anti-MRSA antibiotic. Studies in adults have demonstrated a high negative predictive value (NPV) of MRSA nasal swabs (MNS) in a variety of infectious syndromes. Negative MNS have been utilized as a tool to guide de-escalation of anti-MRSA antibiotics in adults, especially in those with lower respiratory tract infections, but data in children is minimal. The primary objective of this study was to determine the NPV and positive predictive value (PPV) of MNS in children hospitalized for treatment of an infection.

METHODS

This was a single-site, retrospective cohort study of pediatric patients admitted with a suspected infectious diagnosis who had an MNS performed during their hospitalization between June 1, 2018 and November 25, 2022.

RESULTS

This study identified 172 patients who met the inclusion criteria. Eleven (6.4%) nasal swabs were positive for MRSA and 10 (5.8%) microbiological cultures from suspected sources of infection were identified to be positive for MRSA. The MNS was found to have a sensitivity of 20%, specificity of 94%, PPV of 18% and NPV of 95% for all sites of infection.

CONCLUSION

MNS has a high NPV and low PPV in children. MNS can be utilized as an antimicrobial stewardship tool to guide the safe de-escalation of anti-MRSA antibiotics in children.