What is the best approach for a 78-year-old male with Staphylococcus haemolyticus bacteremia on vancomycin (Vancomycin) and right toe cellulitis with possible fungal involvement on Ambisome (Amphotericin B)/Voriconazole (Voriconazole), considering the role of imaging and beta-D-glucan as a biomarker?

Management of Staphylococcus haemolyticus Bacteremia with Toe Cellulitis and Possible Fungal Co-infection

For a 78-year-old male with Staphylococcus haemolyticus bacteremia on vancomycin and right toe cellulitis with possible fungal involvement currently on amphotericin B (Ambisome) and voriconazole, advanced imaging is essential for evaluating disease progression, and beta-D-glucan testing should be used to confirm fungal infection while continuing current antimicrobial therapy.

Role of Imaging in Worsening Infection

• MRI is the preferred imaging modality for detecting bone involvement, deep soft-tissue abscesses, or sinus tracts in patients with worsening toe cellulitis, providing the most accurate assessment of infection extent 1
• Plain radiographs should be obtained initially to evaluate for osteomyelitis, with follow-up imaging in 2-4 weeks if initial films are negative but clinical suspicion remains high 1
• High-resolution ultrasonography or CT scanning may be helpful specifically for detecting deep soft-tissue abscesses or sinus tracts that might require drainage 1
• Nuclear medicine scans (especially those with labeled leukocytes) are highly sensitive and may be useful in some cases but are generally less specific than MRI 1
• For patients with worsening infection despite appropriate therapy, imaging should be performed to assess for complications such as abscess formation requiring surgical intervention 1

Role of Beta-D-Glucan Testing

• Blood cultures should be obtained and skin lesions should be aggressively evaluated by culture aspiration, biopsy, or surgical excision, as they may be caused by resistant microbes, yeast, or molds 1
• Beta-D-glucan testing can help confirm fungal involvement, though sensitivity of a single-serum fungal antigen test is low, particularly in patients already receiving antifungal agents 1
• Tissue samples should be obtained whenever possible for culture, as they generally provide more accurate results than superficial swab specimens 1
• For definitive diagnosis of fungal infection, biopsy or aspiration of the lesion(s) to obtain material for histological, cytological, and microbiological evaluation is recommended 1

Treatment Approach

For Staphylococcus haemolyticus Bacteremia

• Continue vancomycin for Staphylococcus haemolyticus bacteremia, ensuring appropriate dosing to maintain trough concentrations of 15-20 μg/mL in severe infections 1
• Consider adding a beta-lactam agent (such as piperacillin-tazobactam) to the vancomycin regimen for severe non-purulent skin and soft tissue infections with systemic signs of infection 1
• For persistent bacteremia, evaluate for metastatic foci of infection using appropriate imaging modalities 2
• Duration of antimicrobial therapy should be at least 2 weeks after clearance of bloodstream infection 1

For Possible Fungal Co-infection

• Continue current antifungal therapy with amphotericin B (Ambisome) and voriconazole while awaiting definitive diagnosis 1
• If Aspergillus is confirmed, voriconazole is the preferred treatment (strong recommendation), with a 53% response rate as primary therapy compared to 32% with amphotericin B alone 3
• For Candida infections, an echinocandin should be used, or if Candida parapsilosis is isolated, lipid formulation amphotericin B is recommended 1
• For Mucor/Rhizopus infections, lipid formulation amphotericin B or posaconazole is recommended 1
• Treatment duration for fungal infections should be 6-12 weeks for Aspergillus and 2 weeks after clearance of bloodstream infection for Candida 1, 3

Surgical Considerations

• Debridement is crucial for removing necrotic tissue and slough, reducing pressure at callused sites, removing colonizing bacteria, and facilitating collection of appropriate specimens for culture 1
• Use a sterile, blunt metal probe to measure the depth and extent of the wound, noting any foreign bodies, soft-tissue abscesses, communications with joint cavities or tendon sheaths, or palpable bone 1
• Surgical intervention is recommended for drainage of soft tissue abscess, especially for progressive polymicrobial infection 1
• Complex abscesses typically respond to incision and drainage with adjuvant antibiotic therapy 1

Monitoring and Follow-up

• Monitor for clearance of bacteremia with serial blood cultures 2
• Following debridement, measure and record the wound size, extent of surrounding cellulitis, and quality and quantity of drainage to assess healing progress 1
• Evaluate for persistent fever, which may indicate inadequate source control, resistant organisms, or fungal co-infection 1
• Consider repeat imaging if clinical improvement is not observed within 5-7 days of appropriate antimicrobial therapy 1

Special Considerations for Elderly Patients

• Elderly patients may have atypical presentations of infection with less pronounced inflammatory signs 1
• Assess for underlying conditions that may complicate treatment, such as peripheral vascular disease or neuropathy 1
• Carefully monitor renal function with vancomycin therapy, as elderly patients are at higher risk for nephrotoxicity 1
• Consider potential drug interactions between antifungal agents and other medications the patient may be taking 3