2181. Yield and Impact of Molecular Diagnostics for Pathogen Detection in Pediatric Patients: 16/18S rRNA PCR and Noninvasive Assays

Abstract

BackgroundMolecular diagnostic tests can identify bacterial and fungal pathogens from clinical samples. Nucleic acid detection tests include 16S and 18S rRNA gene PCR (16/18S PCR) and plasma next-generation sequencing (NGS). Other assays (fungal galactomannan and 1,3-β-d-glucan) detect structural factors. Our objective was to assess the utilization, yield, and impact of molecular diagnostics in pediatric patients who had samples sent for 16/18S PCR.MethodsSterile site fluid or tissue specimens were collected as part of standard care at Lurie Children’s Hospital, cultured, and sent to Northwestern Memorial Hospital for 16/18S PCR as clinically indicated. Medical records were reviewed for diagnostics, antibiotics, and clinical course.ResultsFrom 1/2016–8/2018, 236 samples were sent for 16 and/or 18S PCR from 183 patients. 83% had a concurrent ID consult. 16S PCR was done on 215 samples, 42 (20%) were positive, and 36 yielded species identification (Table 1). Antibacterial agents were administered prior to specimen collection in 73% and did not affect likelihood of positive 16S PCR. 18S PCR was sent on 163 samples; 12 (7.4%) were positive (Table 2) of which 10 were from immunocompromised hosts. 40% of patients were on antifungals prior to sample acquisition. 16/18S PCR impacted antimicrobial decision-making in 70 cases (30%). A pathogenic fungus was detected by PCR but not culture in 2 cases. Time to positivity of fungal culture was 1–15 days. Fungal culture was positive in 5 cases with-negative 18S PCR. Seventeen patients had positive serum 1,3-ß-D-glucan and/or galactomannan: 3 of which had positive 18S PCR, 5 with fungal growth, 5 presumed infection based on imaging, 1 Nocardia, and 3 noninfectious etiology. Plasma NGS was sent on 45 cases, was positive in 34, and affected clinical management in 10.Conclusion16S PCR can identify bacterial pathogens in the setting of negative culture and impact clinical care. Abscess, bronchial/pleural fluid, and brain/organ tissue were high yield specimens. 18S PCR can provide expeditious fungal identification in cases of suspected invasive disease, but fungal culture and serum molecular testing increase diagnostic yield. No single fungal test is comprehensive. Plasma NGS had relatively high yield and clinical impact in selected patients. Disclosures All authors: No reported disclosures.