(1195) Respiratory Culture Results and Antibiotic Use in a Large Cohort of Mechanically Ventilated Patients

Introduction: Critically ill patients who require mechanical ventilation (MV) are at high risk for respiratory infection. Respiratory cultures are often obtained to identify bacteria and guide more precise antibiotic treatment for infection.

Methods: This retrospective descriptive study 1) assessed respiratory cultures in a cohort of 513 critically ill MV patients enrolled in a clinical trial; 2) described the most common potential pathogens; and 3) assessed antibiotic administration pre and post culture results. Following consent within 24 hours of intubation, patients were followed for up to 14 days of MV. Demographic and outcome variables were recorded. Data were analyzed using descriptive statistics.

Results: Patients were diverse: 58% male, 74% white, 26% racially diverse, and 19% Hispanic ethnicity; mean age 58.8+18.8; and ventilated a median of 107h. Respiratory cultures were ordered for 341 (67%) patients. Types were 35% miniBAL; 60% tracheal aspirate; and 5% bronchoscopy. Positive results were identified in 136 (40%) of cultures (27% of patients enrolled). One primary pathogen was identified in 87% of samples while 13% had two or more pathogens. Bacteria identified were: 22% Candida, 13% Staphylococcus, 8% Klebsiella, 6% Serratia, 5% Pseudomonas, 5% Escherichia, 4% Stenotrophomonas, 3% Enterobacter, 2% MRSA, 1% Acinetobacter, and 30% combined other. Antibiotic administration was common with 44% of all patients prescribed an antibiotic on day of admission, 48% on day 2, and 45% day 3. Following results, a new antibiotic was ordered for 50% of patients with a positive culture.

Conclusions: A high percentage of MV patients present with symptoms of respiratory infection and respiratory cultures were ordered. Based on culture results, 27% of patients had one or more potential respiratory pathogens identified, yet nearly half of patients were prescribed antibiotics within the first three days of MV. Candida was the most common pathogen identified in this study. Broad spectrum antibiotic usage promotes fungal growth, contributing to this finding. The need for early administration of antibiotics in critically ill patients without quantitative culture results should be carefully evaluated.