Procalcitonin Guided Antibiotic Therapy

Inclusion Criteria: * ≥ 18 years old * Ability to give consent in English or Spanish * Imaging proven intra-abdominal infection (CT, US, and/or MRI) Exclusion Criteria: * Unable to give informed consent * Patients enrolled in another trial * Those having surgery for source control * Patients with anastomotic leak * Unable or unwilling to return or be contacted for clinical follow-up visits * Currently incarcerated in a detention facility or in police custody * Conditions with altered immune response or at risk for bacterial seeding * Immunodeficiency (e.g., absolute neutrophil count \<500/mm3, chronic immunosuppressive drugs, active chemotherapy or plans for chemotherapy in the following 30 days, or known AIDS \[CD4 count \<200 or AIDS-defining illness within the last year\] assessed by patient history) * Uncompensated liver failure * Taking medication to treat active inflammatory bowel disease * Malignancy, not in remission (ongoing chemotherapy patients excluded) * Pregnant or expectation of becoming pregnant in the 30 days following baseline/screening * Expected concurrent hemodialysis, peritoneal dialysis, or treatments using indwelling venous catheters * Recent (within 90 days) placement of surgical implant (e.g., pacemaker, joint prosthesis, mechanical valve) * Indwelling Left Ventricular Assist Device * Patients with another infection (e.g., pneumonia, urinary tract infection) that requires treatment with another antibiotic