Microbiology, Antibiotic Choice, and Pre-op Factors: Appendicitis Outcomes and Antibiotic Stewardship

Background: Appendicitis is the most common pediatric surgical emergency and is a common reason for inpatient pediatric antibiotic use. Understanding pathogen prevalence and other factors which may play a role in severity or complications, may aid in appropriate antibiotic (abx) choice and in providing optimal and safe care.

Methods: We performed a retrospective chart review of complicated appendicitis (CA) patients with or without adverse outcomes (including but not limited to post op abscess, sepsis, readmissions) admitted 2013-2015 to Stony Brook Children’s Hospital. Since 2013, all appendicitis patients have had peritoneal cultures and followed a standardized antibiotic protocol; it recommended IV piperacillin-tazobactam (P/T) for pre-op abx if concern for sepsis, WBC count >20, or perforation on imaging; and for post-op abx if met criteria for CA based on operative findings; others received IV cefoxitin. Data was analyzed by chi-square as categorical variables in SPSS.

Results: 79 subjects with CA were analyzed. 24/79 (30%) had adverse outcomes; the most common was abscess formation (42%). Compliance with the pre-op antibiotic protocol was 63%; post-op protocol was 86%. Abnormal BMI (LR 8.2, p=.005), initial band count >10% (LR 4.2, p=.03), no abdominal pain on presentation (LR 10, p=.002), and culture positivity (LR 7.9, p=.023) were all associated with adverse outcomes. No association was seen with age/sex/ethnicity, symptom days, WBC/neutrophil count, and perforation on imaging, appendix pathology or type or number of bacteria isolated. 15% of cultures had no growth. The most common pathogen isolated was E. coli (43% ampicillin resistant, 7% ampicillin-sulbactam resistant, 2% P/T resistant, none 3^rd-gen. cephalosporin resistant). Pseudomonas was isolated in only 8% of cultures. No association was seen with outcome & antibiotic susceptibility; only 1 organism was resistant to P/T.

Conclusion: Identifying key factors may help risk-stratify children with CA and allow for earlier optimal surgical/antibiotic management. Resistance to protocol antibiotics did not correlate with poor outcomes though overall culture positivity did, suggesting intra-op cultures can be generally useful but further stewardship interventions is possible.