# P-948. Performance Characteristics of MRSA Nares PCR in Pediatric Lower Respiratory Tract Infections: A Prospective Evaluation

## TL;DR

This study shows that MRSA nasal PCR testing is highly reliable for ruling out MRSA in children with lung infections, helping reduce unnecessary antibiotic use.

## Contribution

The study provides new prospective data on MRSA nares PCR performance in pediatric lower respiratory tract infections.

## Key findings

- MRSA nares PCR had 100% sensitivity and negative predictive value with no false negatives.
- Specificity was 93.9%, but positive predictive value was lower at 40%.
- The test supports early de-escalation of anti-MRSA therapy in critically ill children.

## Abstract

Inappropriate antibiotic use contributes to antimicrobial resistance and adverse drug events. Empiric anti-MRSA therapy is commonly used in pediatric lower respiratory tract infections (LRTIs), though often unnecessarily. While retrospective studies have shown MRSA nasal swabs have high negative predictive value (NPV), prospective pediatric data remain limited. This study evaluates the diagnostic performance of MRSA nares PCR in hospitalized children with suspected LRTIs.

Summary of Patient-Level Data and Test Characteristics for MRSA Nares PCR EvaluationTable 1.Patient Demographics and Clinical CharacteristicsTable 2.Diagnostic Performance of MRSA Nares PCR Testing

Patient Demographics and Clinical Characteristics

Diagnostic Performance of MRSA Nares PCR Testing

We conducted a prospective, single-center study of hospitalized children (< 18 years) undergoing evaluation for LRTIs. MRSA nares PCR results were compared to lower respiratory tract cultures (LRTC), including tracheal, endotracheal, sputum, or BAL specimens. Immunocompromised or neutropenic patients were excluded. Informed consent was obtained. We calculated sensitivity, specificity, positive predictive value (PPV), and NPV of MRSA nares PCR in predicting MRSA from LRTC.

Among 102 patients (mean age 7.0 years; 55.9% male), 10 (9.8%) had positive MRSA nares PCR and 4 (3.9%) had culture-confirmed MRSA. Sensitivity and NPV were 100%, with no false negatives. Specificity was 93.9%, and PPV was 40%. Among 15 patients who received >72 hours of MRSA therapy before PCR testing, one had a positive PCR but all cultures were negative. Most patients (83.3%) required oxygen support. Mechanical ventilation was required in 50% for acute illness, and 27.5% were ventilated at baseline. Final diagnoses included pneumonia (25.5%), non-infectious conditions (25.5%), and tracheitis (18.6%). MRSA PCR was collected before antibiotics in 36.3% and ≥72 hours after antibiotics in 17.6%.

MRSA nares PCR is a reliable rule-out test in pediatric LRTIs. Its high NPV supports early de-escalation of anti-MRSA therapy, including in critically ill patients. It offers value in antimicrobial optimization, particularly when cultures are delayed or unobtainable.

Michael D. Green, MD, MPH, ADMA: Advisor/Consultant|Bristol Myers Squibb: Advisor/Consultant|ITB-MED: Advisor/Consultant Evan E. Facer, DO, AbbVie, Inc.: Grant/Research Support