What is the management approach for an adult patient with underlying health conditions and Acinetobacter iwoffii bloodstream infection, possibly acquired in a hospital setting?

Management of Acinetobacter iwoffii Bloodstream Infection

Critical Initial Recognition

Acinetobacter iwoffii bloodstream infections should be managed with the same antimicrobial approach as A. baumannii complex infections, as routine clinical laboratories need not distinguish between species for treatment purposes, and all Acinetobacter species causing bacteremia in hospitalized patients warrant aggressive therapy. 1, 2

While A. iwoffii is generally less virulent than A. baumannii, it represents an opportunistic pathogen capable of causing serious bacteremia with associated morbidity and mortality, particularly in patients with underlying conditions. 3

Immediate Infection Control Measures

Contact precautions must be implemented immediately for all patients with any Acinetobacter species infection or colonization. 4

• Institute strict contact precautions upon identification 4
• Implement alert codes to identify the patient promptly if readmitted 4
• Examine all aspects of room and medical equipment cleaning, with clear responsibility assignments 4
• Use hypochlorite solutions (0.5%) for room and surface cleaning 4

Antimicrobial Treatment Algorithm

Step 1: Obtain Cultures and Initiate Empirical Therapy

Obtain blood cultures and susceptibility testing before initiating therapy, but do not delay treatment in critically ill patients. 5, 1

For empirical coverage while awaiting susceptibilities:

• Start carbapenem therapy (imipenem, meropenem, or doripenem) if the patient is in a setting with low carbapenem resistance rates 5, 2
• Consider combination therapy with two agents if the patient presents with severe sepsis or septic shock 5, 1

Step 2: Definitive Therapy Based on Susceptibility Results

If Carbapenem-Susceptible:

Use carbapenem monotherapy (imipenem, meropenem, or doripenem) as the drug of choice. 5, 2, 6

• Never use ertapenem, as it lacks activity against Acinetobacter species 5, 1
• Standard carbapenem dosing is appropriate for bloodstream infections 5

If Carbapenem-Resistant but Sulbactam-Susceptible:

Ampicillin-sulbactam is the preferred option over polymyxins based on superior mortality outcomes. 5, 1

• Dose: 3g sulbactam component every 8 hours as a 4-hour infusion (for isolates with MIC ≤4 mg/L) 5
• Higher doses up to 16g every 8 hours may be used for severe infections 1
• Sulbactam has intrinsic activity against Acinetobacter independent of its β-lactamase inhibitor properties 5

If Resistant to Both Carbapenems and Sulbactam:

Intravenous polymyxins (colistin or polymyxin B) are the recommended agents. 1, 2

• Colistin dosing: Loading dose of 9 million IU, followed by maintenance of 4.5 million IU every 12 hours, adjusted for renal function 5, 1, 2
• Polymyxin B may be preferred: 1.5-3 mg/kg/day with a loading dose of 2-2.5 mg/kg, as it causes less nephrotoxicity than colistin 2
• Never omit the loading dose of colistin 1

Step 3: Combination vs. Monotherapy Decision

For definitive therapy when susceptibilities are known, use monotherapy with an active agent, except for patients remaining in septic shock or at high risk for death. 1

When combination therapy is indicated:

• Use two in vitro active agents for severe carbapenem-resistant infections with septic shock 5, 1
• Avoid colistin plus rifampin (lacks proven benefit) 4, 5
• Avoid colistin plus glycopeptides (increases nephrotoxicity without added benefit) 4, 5
• Consider sulbactam or polymyxin with a second agent (tigecycline, rifampicin, or fosfomycin) only for clinical failures or infections with MIC at the upper limit of susceptibility 4, 5

Treatment Duration

Maintain antimicrobial therapy for 2 weeks for bacteremia, especially in cases manifesting as severe sepsis or septic shock. 4, 5, 1

• Shorter durations may be acceptable for less severe infections without complications 4
• Duration depends on clinical response and source control 4

Critical Monitoring Requirements

Nephrotoxicity Surveillance

Monitor renal function closely throughout therapy, as nephrotoxicity occurs in up to 53.7% of patients receiving colistin. 1, 2

• Polymyxin B causes less nephrotoxicity than colistin (preferred when available) 1, 2
• Check serum creatinine at baseline and daily during polymyxin therapy 5

Clinical Response Assessment

Monitor for clinical response and consider repeat blood cultures to document clearance. 5

• Assess fever curve, hemodynamic stability, and inflammatory markers 5
• Obtain repeat blood cultures 48-72 hours after initiating appropriate therapy 5

Critical Pitfalls to Avoid

Never use tigecycline as monotherapy for bacteremia due to suboptimal serum concentrations and higher treatment failure rates. 5, 1

Never use aminoglycoside monotherapy for serious Acinetobacter infections. 1

Never assume carbapenem susceptibility in endemic areas or during outbreaks without testing. 1

Never delay empirical coverage in previously colonized patients presenting with severe sepsis. 1

Source Control Considerations

• Identify and remove any intravascular catheters that may be the source of infection 7
• The lower respiratory tract and intravascular catheters are the most frequent sources of Acinetobacter bacteremia 7
• Ensure adequate drainage of any abscesses or infected fluid collections 6

Antibiotic Stewardship

An antibiotic stewardship program is indispensable in controlling Acinetobacter infections and preventing resistance emergence. 4, 1

• De-escalate to narrower spectrum agents once susceptibilities are available 1
• Avoid prolonged courses of broad-spectrum antibiotics when not indicated 1