Diagnostic yield and clinical impact of microbiologic diagnosis from CT-guided drainage in patients previously treated with empiric antibiotics Kathryn L. McGillen, 1,2 Johannes Boos, 1 Ruvandhi Nathavitharana, 3 Alexander Brook, 1 Maryellen R. Sun, 1 Bettina Siewert, 1 Vassilios Raptopoulos, 1 Robert Kane, 1 Robert Sheiman, 1 Olga R. Brook 1 1 Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, USA 2 Penn State Hershey Radiology, Hershey, PA, USA 3 Department of Medicine, Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Boston, MA, USA Abstract Purpose: 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. Methods: This retrospective, HIPAA-compliant, IRB- approved study reviewed records of 300 consecutive patients who underwent CT-guided aspiration or drai- nage 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. Results: 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 collec- tions; 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 (me- dian 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 leuko- cytosis (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. Conclusions: Despite predrainage antibiotic therapy, CT- guided drainage demonstrates a high yield of positive cultures and influences clinical management in the major- ity of patients. Key words: Abscess drainage—Culture—CT-guided Hospitalized patients with infectious symptoms are often placed on empiric antibiotic therapy in accordance with accepted clinical guidelines, particularly at-risk popula- tions such as those who are postoperative, neutropenic, or who have presumed hospital-acquired infections [1–3]. Fluid collections later discovered in patients who have been empirically treated with antibiotics for other clini- cally diagnosed infections present a diagnostic dilemma as to whether the fluid collection was a source of the patient’s infectious symptoms or was an incidental finding such as seroma, loculated ascites, or other sterile fluid collection. Where fluid collections are infectious, Correspondence to: Johannes Boos; email: jboos@bidmc.harvard.edu ª Springer Science+Business Media New York 2016 Published online: 21 September 2016 Abdominal Radiology Abdom Radiol (2017) 42:298–305 DOI: 10.1007/s00261-016-0833-5