Diagnostic yield and clinical impact of microbiologic diagnosis from CT-guided drainage in patients previously treated with empiric antibiotics

The purpose of the study was to evaluate diagnostic yield and the added value of culture results on the clinical management of patients empirically treated with antibiotics prior to CT-guided drainage.

This retrospective, HIPAA-compliant, IRB-approved study reviewed records of 300 consecutive patients who underwent CT-guided aspiration or drainage for suspected infected fluid collection while on empiric antibiotics (11/2011 to 9/2013) at a single institution. Patient imaging and clinical characteristics were evaluated by an abdominal imaging fellow and culture results, and patient management were evaluated by an infectious diseases fellow.

After exclusion of 14/300 (4.6%) patients who were not on empiric antibiotics and 8/300 (2.6%) patients in which no culture was acquired, 278 patients (average age 55 ± 16 years; M:F ratio 54:46) constituted the final study cohort. Leukocytosis was present in 163/278 (59%), and fever in 65/278 (24%). The average collection size was 8.5 ± 4.2 cm with gas present in 140/278 (50%) of collections; median amount drained was 35 mL, and visibly purulent material was obtained in 172/278 (63%). 236/278 (85%) received drains and the remainder were aspirated only. Average time between initiation of antibiotics and start of the drainage procedure was 4.1 ± 6.4 days (median 1.7 days). Cultures were positive in 205/278 (74%) patients with a resulting change in management in 181/278 (65%) cases. The change in management included change of antibiotics in 71/278 (26%), narrowing the antibiotic regimen in 94/278 (34%), and cessation of antibiotics in 16/278 (6%). Multidrug-resistant bacteria were cultured in 53/278 (19%). Several factors were found to be statistically significant predictors of positive cultures: patient leukocytosis (sens 62%, spec 53%), gas in the collection on CT (sens 59%, spec 77%), purulent material aspiration (sens 76%, spec 76%), and presence of polymorphonuclear cells in the specimen.

Despite predrainage antibiotic therapy, CT-guided drainage demonstrates a high yield of positive cultures and influences clinical management in the majority of patients.