(554) Development of a Cystic Fibrosis Specific Antibiogram Evaluating Antimicrobial Susceptibility and Resistance Patterns amongst Pediatric, Adolescent, and Young Adult Patients

Background: Patients with Cystic Fibrosis (PwCF) are at risk for experiencing pulmonary exacerbations related to acute and/or chronic respiratory infections from various organisms. Treatments for infection are primarily driven by historical culture results and response to antibiotic therapy measured by overall improvement in clinical status and FEV1. When choosing between empiric treatment regimens for PwCF it is prudent to understand the uniqueness of the CF microbiome in its level of diversity and complexity. Population specific factors such as genetic mutations in CFTR, age, disease burden, sex, and modulator eligibility play a role in culture positivity and organism susceptibility. Such variables make a larger, generalized antibiogram for an institution flawed in its applicability to the CF population. The purpose of this initiative was to collate respiratory culture results over a one year time period to develop an annualized center specific antibiogram for PwCF.

Methods: A single pediatric center retrospective chart review was conducted across all PwCF followed at our site. Cultures were collected over one year and included those from throat, sputum, endotracheal, or bronchial sites. Cultures screening for acid fast bacilli (AFB) were also included. All cultures were conducted following our institutional CF protocol plated to Burkholderia selective agar. Data elements extracted included demographics, number of cultures/isolates collected, degree of culture growth, organism genus and species, incidence of organism positivity throughout the study time period, and organism susceptibility patterns.

Results: Three hundred cultures were collected between January 2021 through December 2021 amongst 61 patients (n=61) who were 8 months to 24 years of age. PwCF on CFTR modulatory therapy constituted 65.6% of the patient population (n¹ = 40) of which 38 patients were prescribed elexacaftor/tezacaftor/ivacaftor therapy. The majority of cultures obtained were from the throat (69.3%) followed by sputum (23%). The primary organism identified in 109 cultures was Methicillin-susceptible Staphylococcus aureus (MSSA) followed by Haemophilus parainfluenzae (H. paraflu) identified in 95 cultures and Methicillin-resistant Staphylococcus aureus (MRSA) in 25 cultures. MSSA demonstrated 100% susceptibility to all tested antimicrobials except clindamycin (86% susceptible). MRSA demonstrated 0% susceptibility to cefazolin and oxacillin, 60% susceptibility to clindamycin, and 96% susceptibility to sulfamethoxazole/trimethoprim. Pseudomonas was present in 4% of cultures, with 83% susceptible to tobramycin and 75% susceptible to ciprofloxacin. Amongst all cultures collected two were positive for AFB resulting in growth of Mycobacterium kansasii and Mycobacterium avium complex respectively.

Conclusions: In an effort to provide a more focused approached to patient centered care, the development of a CF center specific antibiogram should be considered to characterize the susceptibility patterns of microorganisms commonly identified in the CF airway to give providers additional information when considering empiric antibiotic regimens. Ultimately, the CF antibiogram developed should be compared to the overall institution specific antibiogram to identify similar trends or contrasting results. Future investigation is warranted to collect data on an annual basis to enhance the validity and applicability of the antibiogram over time given the potentially limited number of patients followed at a CF care center.

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