What is the diagnosis and appropriate management for a post-surgical patient with a surgical site infection (SSI) and intra-abdominal infection, presenting with erythema, warmth, tenderness, serosanguineous drainage, and positive wound culture for E. coli and yeast, who is currently being treated with ertapenem (a carbapenem antibiotic) and micafungin (an antifungal agent)?

Diagnosis: Complicated Intra-Abdominal Infection with Surgical Site Infection

This patient has a deep surgical site infection (SSI) that has progressed to a complicated intra-abdominal infection, specifically manifesting as focal enteritis/enterocolitis with contained perforation or microperforation, evidenced by the CT findings of circumferential ileal wall thickening, extraluminal air, and mesenteric fat stranding. The current antimicrobial regimen of ertapenem and micafungin is appropriate and should be continued 1, 2.

Clinical Diagnosis Breakdown

Deep SSI with Organ/Space Extension

• The initial presentation with erythema, warmth, tenderness, serosanguineous drainage, and purulent material from the midline incision represents a deep SSI that has extended beyond the fascial layers 1
• The CT findings of mesenteric fluid collection, ileal wall thickening with extraluminal air, and fat stranding indicate progression to an organ/space SSI involving the intra-abdominal cavity 1
• This represents a complicated intra-abdominal infection requiring both source control (which has been achieved through wound opening and drainage) and antimicrobial therapy 1

Microbiology and Pathogen Coverage

• The wound culture growing E. coli and yeast is consistent with post-operative intra-abdominal infection following intestinal surgery 1, 3
• E. coli is the most common pathogen in complicated intra-abdominal infections (71% of cases) and SSIs following abdominal surgery 1, 3
• The presence of yeast (Candida species) in the setting of post-surgical infection with ongoing contamination warrants antifungal therapy 1

Current Management Assessment

Antimicrobial Therapy - Appropriate and Should Continue

The combination of ertapenem plus micafungin is the correct empiric regimen for this healthcare-associated complicated intra-abdominal infection with documented E. coli and yeast.

• Ertapenem is FDA-approved for complicated intra-abdominal infections caused by E. coli and provides coverage for the polymicrobial flora typical of these infections, including anaerobes like Bacteroides fragilis 2
• Ertapenem has demonstrated equivalent efficacy to piperacillin-tazobactam and other comparators in multiple randomized trials for complicated intra-abdominal infections 4
• Micafungin appropriately covers the documented yeast infection, which is critical in healthcare-associated intra-abdominal infections 1

Source Control - Adequately Achieved

• Opening the wound with staple removal and purulent drainage represents appropriate source control for the superficial component 1
• The patient's clinical improvement (resolution of abdominal pain, tolerating oral intake, passing flatus, having bowel movements) indicates that adequate source control has been achieved for the intra-abdominal component without need for surgical re-exploration 1
• Daily iodoform packing with wound improvement confirms appropriate local wound management 1

Duration of Antimicrobial Therapy

Continue ertapenem and micafungin until clinical resolution is complete, typically 4-7 days of therapy, but potentially longer given the complexity of this case.

• For complicated intra-abdominal infections, antimicrobial therapy should be limited to 4-7 days unless source control is difficult to achieve 1, 5
• Given the documented extraluminal air and contained perforation, this patient may require therapy toward the longer end of this spectrum 1
• Clinical markers for discontinuation include: normalized temperature, normalized white blood cell count, resolution of abdominal pain, tolerance of oral diet, and return of bowel function 1, 6
• The patient is already demonstrating these favorable signs (no abdominal pain, tolerating full liquids, passing flatus, having bowel movements), suggesting therapy can likely be completed within the standard timeframe 1

Monitoring for Treatment Failure

If clinical improvement plateaus or reverses after 4-7 days of therapy, obtain repeat CT imaging to evaluate for persistent or recurrent infection.

• Patients with persistent fever, leukocytosis, failure of bowel function to normalize, or recurrent abdominal pain after 4-7 days require repeat imaging (CT is preferred) to identify undrained collections or ongoing infection 1
• Continue antimicrobial therapy while investigating potential treatment failure 1
• Consider extra-abdominal sources of infection (pneumonia, urinary tract infection, C. difficile) and non-infectious causes (venous thrombosis, pulmonary embolism) if no intra-abdominal source is identified 1

Critical Management Points

Do Not Narrow Antimicrobial Spectrum Prematurely

• While E. coli and yeast were isolated, the CT findings of ileal inflammation with extraluminal air suggest ongoing polymicrobial infection that may include anaerobes not captured in the superficial wound culture 1
• Ertapenem provides essential anaerobic coverage (including Bacteroides fragilis) that would be lost if switched to a narrower agent 2, 4
• Maintain broad-spectrum coverage until clinical resolution is complete 1, 6

Wound Care Continuation

• Continue daily iodoform packing changes until the wound heals by secondary intention 1
• The wound is showing appropriate improvement with decreased drainage 1

Immunotherapy Considerations

• Appropriately, steroids and immunotherapy have been held given the active infection [@case presentation@]
• Do not restart immunotherapy until the infection has completely resolved, antimicrobials have been discontinued, and the wound has substantially healed 1
• Ensure infectious disease and oncology follow-up for coordinated re-initiation of immunotherapy [@case presentation@]

Antibiotic Stewardship Considerations

• Once the patient completes 4-7 days of IV therapy with documented clinical improvement, consider transition to oral step-down therapy if culture susceptibilities allow 1
• For E. coli, oral options include fluoroquinolones (if susceptible) plus metronidazole, or amoxicillin-clavulanate if susceptible 1
• However, given the yeast co-infection, IV therapy may need to continue until both bacterial and fungal components are adequately treated 1