10.1 Infections in Solid Organ Transplant and Hematologic Malignancy

Infections in Solid Organ Transplant and Hematologic Malignancy

Immunocompromised patients—encompassing solid organ transplant (SOT) recipients, allogeneic hematopoietic cell transplant (HCT) recipients, and individuals undergoing intensive cytotoxic chemotherapy for hematologic malignancies—present unique clinical challenges. Immune dysfunction in these populations is multifaceted, combining impaired cell-mediated immunity (T-cell depletion or calcineurin inhibition), disrupted humoral immunity, chemotherapy-induced neutropenia, and breached anatomical barriers. Timely identification and aggressive, targeted pharmacotherapy are essential to avoid catastrophic allograft loss or mortality.

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Timetable of Infection After Solid Organ Transplantation

The susceptibility of solid organ transplant recipients to specific infectious etiologies follows a predictable chronological framework originally elucidated by Fishman and Rubin. This timetable reflects the interplay between epidemiologic exposures and the "net state of immunosuppression"—a composite measure of the dose, duration, and specific modalities of immunosuppressive therapy (induction agents, calcineurin inhibitors, antimetabolites, corticosteroids, mTOR inhibitors), metabolic disturbances (uremia, hyperglycemia, malnutrition), and immunomodulating viral co-infections (CMV, EBV, HHV-6).

                     Chronological Timetable of Post-Transplant Infections

   Early Phase (<1 Month)      Intermediate Phase (1-6 Months)       Late Phase (>6 Months)
 ┌─────────────────────────┐   ┌───────────────────────────────┐   ┌─────────────────────────┐
 │ Surgical site infections│   │ Peak immunosuppression era    │   │ Stable maintenance:     │
 │ Anastomotic leaks       │   │ CMV reactivation / disease    │   │  Community-acquired     │
 │ Hospital pathogens:     │   │ EBV & PTLD                    │   │  respiratory & urinary  │
 │  - MRSA, VRE            │   │ HSV, VZV, HHV-6/7             │   │  infections (S. pneumo, │
 │  - P. aeruginosa        │   │ BK polyomavirus (BKVN)        │   │  influenza, SARS-CoV-2) │
 │  - Enterobacterales     │   │ Pneumocystis jirovecii (PJP)  │   │                         │
 │  - C. difficile         │   │ Listeria, Nocardia            │   │ Chronic rejection /     │
 │  - Candida wound/line   │   │ Toxoplasma gondii             │   │ augmented therapy:      │
 │ Donor-derived infections│   │ Endemic / dimorphic fungi     │   │  Aspergillus, Mucorales │
 │  (rabies, LCMV, WNV)    │   │ Cryptococcus neoformans       │   │  Cryptococcus, Nocardia │
 └─────────────────────────┘   └───────────────────────────────┘   │  Atypical mycobacteria  │
                                                                   └─────────────────────────┘

1. Early Post-Transplant Period (Month 1: Days 0–30)

During the first month following transplantation, infections mirror those encountered in high-risk non-transplant surgical patients. True opportunistic pathogens are rare unless transmitted directly from the donor or present in the recipient prior to surgery.

• Surgical Complications and Anatomic Dehiscence: Wound dehiscence, hematomas, vascular thromboses, and anastomotic failures (e.g., biliary leaks or strictures in liver recipients, ureteral leaks or obstruction in kidney recipients, bronchial anastomotic dehiscence in lung recipients) create non-draining fluid collections that readily serve as nidi for bacterial and fungal colonization.
• Nosocomial and Healthcare-Associated Pathogens: Exposure to intensive care units, indwelling central venous lines, urinary catheters, and mechanical ventilation predisposes recipients to:
  • Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE).
  • Multidrug-resistant Gram-negative bacilli: Pseudomonas aeruginosa, extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales, and carbapenem-resistant Enterobacterales (CRE).
  • Clostridioides difficile colitis, triggered by perioperative surgical antimicrobial prophylaxis.
  • Candida species: Mucocutaneous, surgical drain site, and catheter-related candidemia (C. albicans, C. glabrata, C. krusei).
• Donor-Derived Infections (DDIs): Unrecognized pathogens transmitted from the donor organ can manifest rapidly during this initial month. Examples include acute bacterial bacteremia present in the donor at procurement, latent fungal infections (e.g., Histoplasma, Coccidioides), and lethal neurotropic viruses (rabies virus, lymphocytic choriomeningitis virus [LCMV], West Nile virus).

2. Intermediate Post-Transplant Period (Months 1–6)

This period represents the epoch of maximal cumulative pharmacologic immunosuppression. Induction therapy effects (such as lymphocyte depletion from antithymocyte globulin or alemtuzumab) peak, while maintenance agents (tacrolimus, cyclosporine, mycophenolate mofetil [MMF], prednisone) maintain sustained trough targets. As a consequence, host cell-mediated (T-lymphocyte) immunity is severely blunted, opening the door for classic opportunistic infections:

• Herpesviruses and Latent Viral Reactivation:
  • Cytomegalovirus (CMV): Viral reactivation, primary infection, CMV syndrome (fever, leukopenia, thrombocytopenia, transaminitis), and tissue-invasive disease (gastroenteritis, pneumonitis, hepatitis).
  • Epstein-Barr Virus (EBV): Uncontrolled B-cell proliferation resulting in Post-Transplant Lymphoproliferative Disorder (PTLD), particularly common in EBV-seronegative recipients (D+/R-) receiving seropositive donor organs.
  • Herpes Simplex Virus (HSV-1, HSV-2) and Varicella-Zoster Virus (VZV): Severe mucosal ulcerations, cutaneous zoster (often multi-dermatomal), or disseminated visceral infection.
  • Human Herpesvirus 6 and 7 (HHV-6/7): Provokes bone marrow suppression, encephalitis, and acts as an immunomodulatory cofactor accelerating CMV disease and allograft rejection.
• BK Polyomavirus (BKPyV): Reactivates in the renal allograft epithelium, manifesting as asymptomatic viruria, progressing to BK viremia, and untreated leading to BK Polyomavirus Nephropathy (BKVN) characterized by interstitial nephritis, tubulitis, and allograft loss. Ureteral stenosis can also occur.
• Opportunistic Intracellular Bacteria and Parasites:
  • Pneumocystis jirovecii pneumonia (PJP): Causes life-threatening hypoxemic respiratory failure characterized by bilateral ground-glass opacities. Routine prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMX) has significantly reduced the incidence during this window.
  • Listeria monocytogenes: Transmitted via contaminated foods, leading to bacteremia and central nervous system (CNS) infections (rhomboencephalitis, cerebritis, or meningitis).
  • Nocardia species (N. asteroides, N. farcinica): Weakly acid-fast, branching filamentous Gram-positive bacilli causing necrotizing cavitary pneumonia, subcutaneous abscesses, and metastatic brain abscesses.
  • Toxoplasma gondii: Highest risk in seronegative heart transplant recipients receiving a seropositive heart (D+/R-), leading to acute myocarditis, pericarditis, pneumonitis, or diffuse encephalitis.
  • Strongyloides stercoralis: Corticosteroid therapy can provoke hyperinfection syndrome or disseminated strongyloidiasis, resulting in filariform larvae traversing the intestinal wall and carrying enteric Gram-negative bacteria into the bloodstream (recurrent polymicrobial Gram-negative bacteremia).

3. Late Post-Transplant Period (>6 Months)

Beyond 6 months, patients bifurcate into two distinct clinical trajectories based on their cumulative allograft health and immunosuppressive burden:

• Group 1: Stable Allograft with Minimal Maintenance Immunosuppression (~80% of patients):
  • These recipients receive low-dose maintenance immunosuppressive regimens (e.g., low-dose tacrolimus and low-dose antimetabolite, often steroid-free).
  • Primary infectious vulnerabilities are community-acquired pathogens identical to the general immunocompetent population: Streptococcus pneumoniae, seasonal respiratory viruses (influenza, respiratory syncytial virus [RSV], SARS-CoV-2), Legionella pneumophila, and uncomplicated urinary tract infections. Their outcomes are generally favorable, though clinical courses can be slightly prolonged.
• Group 2: Patients with Chronic Allograft Rejection or Augmented Immunosuppression (~20% of patients):
  • Recipients who have experienced acute cellular or antibody-mediated rejection, chronic allograft dysfunction, or recurrent CMV disease require augmented or "pulse" immunosuppression (high-dose intravenous methylprednisolone, antithymocyte globulin, rituximab, eculizumab, or plasmapheresis).
  • These patients remain in a chronic hyper-immunosuppressed state, predisposed to late opportunistic and invasive mold infections:
    • Aspergillus species (A. fumigatus, A. flavus, A. niger) and Mucorales (Rhizopus, Mucor, Lichtheimia).
    • Cryptococcus neoformans (subacute meningitis, pulmonary cryptococcoma, skin nodules).
    • Nontuberculous mycobacteria (NTM; e.g., M. avium complex, M. abscessus, M. kansasii) and Mycobacterium tuberculosis.
    • Endemic mycoses (Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis).
    • Late-onset CMV disease (frequently emerging 1 to 3 months following the cessation of universal antiviral prophylaxis).

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Cytomegalovirus (CMV) Prevention and Management in SOT

Cytomegalovirus (human betaherpesvirus 5) remains one of the most consequential opportunistic pathogens in solid organ transplantation. It exerts both direct effects (viral replication leading to febrile neutropenia, hepatitis, colitis, pneumonitis, nephritis) and indirect immunomodulatory effects (upregulation of HLA molecules, cytokine release, accelerated chronic allograft vasculopathy, increased incidence of acute and chronic allograft rejection, and secondary opportunistic bacterial and fungal co-infections).

Donor/Recipient CMV Serostatus Risk Stratification

The pre-transplant IgG serostatus of both the organ donor (D) and recipient (R) dictates the clinical approach to CMV prophylaxis:

1. High Risk: Donor-Positive / Recipient-Negative (D+/R-):
   • The recipient is immunologically naive, lacking CMV-specific memory T-cells and neutralizing antibodies, while receiving an allograft harboring latent viral genomes in endothelial and myeloid cells.
   • Without prophylaxis, 50% to 70% of D+/R- recipients develop active CMV infection or tissue-invasive disease.
   • Universal antiviral prophylaxis is universally recommended.
2. Moderate / Intermediate Risk: Recipient-Positive (D+/R+ or D-/R+):
   • The recipient possesses pre-existing cellular and humoral immunity. Infection occurs through endogenous viral reactivation (R+) or superinfection with a discordant donor viral strain (D+/R+).
   • Symptomatic disease occurs in 15% to 30% without intervention.
   • Prophylaxis or preemptive monitoring is indicated based on transplanted organ and center protocols.
3. Low Risk: Donor-Negative / Recipient-Negative (D-/R-):
   • Risk of CMV transmission is < 5%, arising almost exclusively from contaminated, non-leukoreduced blood products.
   • Universal prophylaxis is not indicated (patients receive acyclovir or valacyclovir for HSV/VZV prophylaxis). All cellular blood products must be CMV-seronegative or leukoreduced.

Prevention Strategies: Universal Prophylaxis versus Preemptive Therapy

Two evidence-based strategies exist for the prevention of CMV disease post-transplant:

                                CMV Prevention Strategies

                 ┌────────────────────────────────────────────────────────┐
                 │     Stratify Pre-Transplant CMV Serostatus (D / R)     │
                 └───────────────────────────┬────────────────────────────┘
                                             │
                   ┌─────────────────────────┴─────────────────────────┐
                   ▼                                                   ▼
         HIGH RISK (D+ / R-)                               MODERATE RISK (R+)
  (or Lung Transplants regardless)                  (Kidney, Liver, Heart, Pancreas)
                   │                                                   │
                   ▼                                                   ▼
       UNIVERSAL PROPHYLAXIS                         CHOICE: PROPHYLAXIS vs PREEMPTIVE
  Valganciclovir 900 mg PO Daily                     ┌─────────────────┴─────────────────┐
  (Adjust for renal function)                        ▼                                   ▼
  Duration:                                 UNIVERSAL PROPHYLAXIS               PREEMPTIVE THERAPY
  - D+/R- Kidney/Pancreas: 6 MONTHS         Valganciclovir 900 mg PO Daily     Weekly CMV quantitative
  - Lung Transplants: 6 to 12 MONTHS        Duration: 3 MONTHS                 plasma DNA PCR for 12-16 wks
  - D+/R- Liver/Heart: 3 to 6 MONTHS                                           Start therapeutic valganciclovir
                                                                               if viral load reaches threshold

1. Universal Antiviral Prophylaxis

• Agent & Dosing: Valganciclovir 900 mg orally once daily (taken with food to optimize bioavailability). The dose must be adjusted rigorously for renal clearance:
  • CrCl ≥ 60 mL/min: 900 mg PO daily.
  • CrCl 40–59 mL/min: 450 mg PO daily.
  • CrCl 25–39 mL/min: 450 mg PO every 48 hours.
  • CrCl 10–24 mL/min: 450 mg PO twice weekly.
  • CrCl < 10 mL/min (hemodialysis): 200 mg PO three times weekly post-hemodialysis.
• Recommended Duration:
  • D+/R- Kidney and Pancreas Transplants: 6 months (supported by the IMPACT trial, which demonstrated that extending valganciclovir from 100 days to 200 days reduced the incidence of CMV disease from 36.8% to 16.1% at 12 months without increasing viral resistance).
  • Lung Transplants: 6 to 12 months (frequently lifelong in some centers due to high mortality from CMV pneumonitis and allograft rejection).
  • D+/R- Liver and Heart Transplants: 3 to 6 months.
  • R+ Moderate-Risk Recipients: 3 months.
• Advantages: Prevents both direct CMV syndrome and indirect immunomodulatory sequelae; prevents other herpesviruses (HHV-6, EBV, HSV, VZV); straightforward operational delivery.
• Disadvantages: High drug costs; significant myelosuppression (leukopenia and neutropenia in up to 30-40% of patients, frequently prompting inappropriate dose reductions); development of late-onset CMV disease (occurring 1 to 4 months following prophylaxis completion due to delayed reconstitution of CMV-specific CD4+ and CD8+ T-cell responses).

2. Preemptive Antiviral Therapy

• Protocol: Serial screening of peripheral blood or plasma using a standardized quantitative CMV DNA real-time PCR assay (reported in IU/mL) every week for the first 12 to 16 weeks post-transplantation.
• Intervention: Antiviral treatment is initiated at a predefined institutional viral load threshold (e.g., >1,000 to 2,000 IU/mL, or lower if a rapidly rising viral doubling time is observed) before clinical symptoms manifest.
• Regimen: Full therapeutic-dose valganciclovir (900 mg PO BID, renal-adjusted) until two consecutive weekly PCR tests are undetectable or below the lower limit of quantification.
• Advantages: Eliminates unnecessary drug exposure and drug toxicity in patients who never reactivate; lower drug acquisition cost; subclinical viral replication promotes endogenous host CMV-specific T-cell immune priming, resulting in significantly lower rates of late-onset CMV disease.
• Disadvantages: Demands rigorous outpatient adherence to weekly blood draws; requires rapid, dependable laboratory turnaround times (<24–48 hours); does not protect against early indirect immunomodulatory allograft injury.

Treatment of Established CMV Infection and Disease

Once active CMV infection (viremia with systemic symptoms) or tissue-invasive CMV disease (end-organ damage) is documented, therapy must be initiated promptly:

• Mild-to-Moderate Disease or Asymptomatic High-Level Viremia: Oral valganciclovir 900 mg PO twice daily (renal-adjusted). The VICTOR trial demonstrated clinical and virologic non-inferiority of oral valganciclovir 900 mg BID compared to intravenous ganciclovir for non-severe CMV disease.
• Severe, Life-Threatening, or High-Viral-Load Disease: (e.g., hypoxemic CMV pneumonitis, severe gastrointestinal ulceration with bleeding/vomiting/malabsorption, meningoencephalitis, or baseline viral load >1,000,000 IU/mL): Intravenous ganciclovir 5 mg/kg IV every 12 hours (adjusted for renal function).
• Monitoring and Duration:
  • Quantitative plasma CMV DNA PCR should be monitored weekly during treatment.
  • Therapy is continued for a minimum of 14 to 21 days, and should never be stopped based on a fixed calendar duration.
  • Treatment must continue until complete resolution of clinical signs and symptoms AND viral clearance documented by undetectable viral load (or < lower limit of quantification) on at least one, and preferably two, consecutive weekly PCR measurements.
  • Secondary Prophylaxis: Following clearance, maintenance prophylaxis (valganciclovir 900 mg PO daily) is routinely continued for 1 to 3 months to prevent immediate recurrence, particularly in D+/R- patients or those requiring continued high-level immunosuppression.

Refractory and Resistant CMV

• Refractory CMV: Characterized by persistent viremia (< 1-log10 decline) or worsening clinical symptoms after ≥ 2 weeks of therapeutic-dose ganciclovir or valganciclovir.
• Resistant CMV: Confirmed presence of viral genetic mutations that confer reduced phenotypic susceptibility to one or more antiviral agents. Prolonged antiviral exposure and sub-therapeutic drug concentrations are the primary drivers.

                      CMV Antiviral Targets and Resistance Mutations

            [Maribavir]
                 │ (competitive ATP-binding inhibition)
                 ▼
            UL97 Kinase ───► Monophosphorylates Ganciclovir
                 │               │
     Mutations:  │               ▼ Host Kinases
     M460V/I     │           Ganciclovir-Triphosphate
     H520Q       │               │
     C594G       │               ▼
     C603W       └───────► UL54 DNA Polymerase ◄─────── [Foscarnet]
     (Ganciclovir-resistant;           │                  (Pyrophosphate-site blocker)
      Maribavir active)                ▼
                              Viral DNA Synthesis
                                       ▲
                                       │
                                  [Cidofovir]
                     (Mutations in UL54 confer cross-resistance
                      between GCV and Cidofovir; some cross to FOS)

Molecular Mechanisms of Resistance

1. UL97 Phosphotransferase Mutations (Common, ~90% of resistant cases):
   • Mechanism: The viral UL97 open reading frame encodes a protein kinase responsible for the essential initial monophosphorylation of ganciclovir (and valganciclovir) into ganciclovir monophosphate. Host cellular kinases subsequently add two additional phosphates to generate active ganciclovir triphosphate.
   • Canonical Mutations: Codon substitutions at M460V/I, H520Q, C594G, L595S, C603W.
   • Resistance Pattern: Confers moderate to high-level resistance to ganciclovir and valganciclovir. UL97 mutants retain full susceptibility to foscarnet and cidofovir because neither drug requires UL97 phosphorylation.
2. UL54 DNA Polymerase Mutations (Less common, but severe):
   • Mechanism: UL54 encodes the catalytic subunit of viral DNA polymerase. Mutations in conserved catalytic domains directly impair drug binding.
   • Resistance Pattern: Emerges almost exclusively in patients with pre-existing UL97 mutations subjected to prolonged, ineffective ganciclovir therapy. Confers high-level resistance to ganciclovir AND high-level cross-resistance to cidofovir. Specific mutations within conserved exonuclease or polymerase domains can also confer cross-resistance to foscarnet.

Pharmacotherapeutic Options for Refractory / Resistant CMV

• Maribavir:
  • Mechanism: An orally bioavailable benzimidazole riboside that inhibits UL97 protein kinase activity through competitive inhibition of ATP binding, blocking viral DNA maturation, capsid nuclear egress, and virion assembly.
  • Indication: FDA-approved for the treatment of refractory CMV infection/disease (with or without genotypic resistance) in adult and pediatric SOT and HCT recipients. (Not indicated for CMV retinitis or encephalitis due to lack of adequate tissue penetration data).
  • Dosing: 400 mg orally twice daily (taken with or without food). No renal dose adjustment is required, making it exceptionally valuable in renal allograft recipients with allograft dysfunction.
  • Critical Interaction: Co-administration with ganciclovir or valganciclovir is strictly contraindicated. Maribavir competitively inhibits UL97 kinase, preventing UL97-mediated monophosphorylation of ganciclovir, resulting in profound antagonistic loss of ganciclovir activity!
  • Adverse Effects: Dysgeusia / taste disturbance (metallic or bitter taste reported in >35% of patients), nausea, diarrhea. Lacks the myelosuppressive toxicity of ganciclovir and the severe nephrotoxicity of foscarnet.
• Foscarnet:
  • Mechanism: An inorganic pyrophosphate organic analogue that non-competitively and directly blocks the pyrophosphate exchange site of viral DNA polymerase without requiring metabolic activation by viral or host kinases. Active against all UL97 mutant strains.
  • Dosing: 90 mg/kg IV every 12 hours or 60 mg/kg IV every 8 hours (heavily renal-adjusted).
  • Toxicities: Severe nephrotoxicity (acute tubular necrosis, crystalline nephropathy); profound electrolyte derangements (hypocalcemia, hypomagnesemia, hypokalemia, hyperphosphatemia/hypophosphatemia); painful genital ulcerations due to high foscarnet concentrations excreted in urine.
  • Supportive Care: Mandatory vigorous intravenous pre-hydration with 500 to 1,000 mL normal saline prior to each infusion, alongside aggressive electrolyte repletion.
• Cidofovir:
  • A nucleotide analogue of cytidine. Highly nephrotoxic (proximal tubular injury leading to Fanconi syndrome and acute renal failure). Requires co-administration with high-dose oral probenecid (to block organic anion transporters in proximal renal tubule cells) and aggressive IV normal saline hydration. Cross-resistant with most UL54 mutations; generally reserved as a third-line salvage agent.
• Letermovir:
  • Inhibits the viral DNA terminase complex (composed of subunits pUL51, pUL56, and pUL89), preventing cleavage and packaging of viral genomic concatemers. Approved for CMV prophylaxis in allogeneic HCT recipients (Day 0 to 100) and high-risk kidney recipients (D+/R-, Day 0 to 200). Has no cross-resistance with UL97 or UL54 mutants. Used off-label in refractory CMV cases, though monotherapy carries a low genetic barrier to resistance via pUL56 substitutions (C325Y/R).
• Adjunctive Management: Reduction of baseline immunosuppressive medications (particularly antimetabolites such as MMF/azathioprine and calcineurin inhibitors) is paramount to allow host cellular immune recovery.

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Febrile Neutropenia in Hematologic Malignancy and HCT

Neutropenia resulting from cytotoxic antineoplastic chemotherapy or myeloablative conditioning for hematopoietic cell transplantation leaves patients vulnerable to invasive bacterial and fungal infections. Because neutrophils are the primary cellular mediators of inflammation, neutropenic patients often lack classic signs of localized infection (erythema, swelling, purulence, pulmonary consolidation). Fever is frequently the sole presenting sign of severe life-threatening sepsis.

Definitions and Clinical Criteria

According to the Infectious Diseases Society of America (IDSA) and National Comprehensive Cancer Network (NCCN) guidelines:

• Fever:
  • A single oral temperature measurement of ≥ 38.3°C (101.0°F), OR
  • A sustained temperature of ≥ 38.0°C (100.4°F) over a duration of > 1 hour.
  • Rule: Rectal temperature measurements, rectal exams, and suppositories are strictly prohibited to prevent micro-trauma to fragile mucosal membranes, which can precipitate bacteremia from enteric organisms.
• Neutropenia:
  • An Absolute Neutrophil Count (ANC) < 500 cells/mm³, OR
  • An ANC expected to fall below 500 cells/mm³ within the subsequent 48 hours.
  • Calculation: ANC = WBC (cells/mm³) × (% Segmented Neutrophils + % Bands) / 100
• Profound Neutropenia: ANC < 100 cells/mm³.
• Prolonged Neutropenia: Duration of neutropenia exceeding 7 consecutive days (characteristic of acute myeloid leukemia induction and allogeneic HCT conditioning).

Risk Stratification: MASCC Risk Index

Patients presenting with febrile neutropenia must be stratified immediately to distinguish candidates for outpatient oral therapy from those requiring urgent hospital admission and parenteral broad-spectrum treatment.

                  Multinational Association for Supportive Care in Cancer (MASCC) Index

  Clinical Characteristic                                                            Points
 ─────────────────────────────────────────────────────────────────────────────────── ──────
  Burden of febrile neutropenia (symptom severity):
    - No symptoms or mild symptoms ..................................................   5
    - Moderate symptoms .............................................................   3
    - Severe symptoms / moribund ....................................................   0
  No hypotension (Systolic Blood Pressure > 90 mmHg) ................................   5
  No Chronic Obstructive Pulmonary Disease (COPD) ...................................   4
  Solid tumor OR Hematologic malignancy with NO previous invasive fungal infection ..   4
  No dehydration requiring parenteral fluid therapy .................................   3
  Outpatient status at onset of fever ...............................................   3
  Age < 60 years ....................................................................   2
 ─────────────────────────────────────────────────────────────────────────────────── ──────
  Maximum Possible Score: 26

• MASCC Score ≥ 21 (Low-Risk Patients):
  • Associated with a < 5% risk of serious medical complications and < 1% mortality.
  • Candidates for oral empiric outpatient therapy if clinical stability criteria are met: hemodynamically stable, no acute organ dysfunction, no pneumonia or catheter-site infection, able to tolerate oral intake, has a dedicated caregiver, and resides within a 1-hour travel radius of an emergency facility with 24/7 access.
  • Oral Regimen: Ciprofloxacin 750 mg PO q12h PLUS Amoxicillin-clavulanate 875/125 mg PO q12h (or 500 mg PO q8h).
  • If penicillin-allergic: Ciprofloxacin (750 mg PO q12h) PLUS Clindamycin (300-450 mg PO q8h).
  • Fluoroquinolone exclusion: If the patient was already receiving prophylactic fluoroquinolone therapy (e.g., levofloxacin prophylaxis during neutropenia), oral fluoroquinolone therapy is contraindicated; the patient must be admitted for IV non-fluoroquinolone antipseudomonal therapy.
• MASCC Score < 21 (High-Risk Patients):
  • High complication risk (up to 40%) and significant mortality.
  • Mandatory inpatient admission and immediate intravenous antipseudomonal monotherapy.
  • Inpatient criteria also include: anticipated neutropenia > 7 days, profound neutropenia (ANC < 100 cells/mm³), hepatic or renal insufficiency, altered mental status, or hemodynamic instability.

Inpatient Empiric Antibacterial Therapy

Empiric antibacterial therapy must be administered within 1 hour of triage ("the golden hour") after obtaining two sets of blood cultures (one peripheral and one from each lumen of every central venous catheter), urine cultures, and chest imaging if respiratory symptoms are present.

1. First-Line Intravenous Monotherapy

Monotherapy with an antipseudomonal beta-lactam that provides bactericidal activity against Pseudomonas aeruginosa, other enteric Gram-negative bacilli, and methicillin-susceptible Staphylococcus aureus (MSSA) is the gold standard:

• Cefepime: 2 g IV every 8 hours (administered as an extended infusion over 3 to 4 hours to maximize time above MIC). Preferred agent; retains excellent Gram-negative potency and activity against viridans streptococci.
• Piperacillin-Tazobactam: 4.5 g IV every 6 hours (or 3.375 g IV every 8 hours via 4-hour extended infusion). Provides anaerobic coverage, making it favorable if intra-abdominal, perianal, or mucosal infection is suspected.
• Meropenem: 1 g IV every 8 hours (or Doripenem 500 mg IV q8h). Reserved for patients with known colonization or previous infection with ESBL-producing organisms, clinical instability/septic shock, or severe immediate-type beta-lactam allergies (using aztreonam if carbapenems are contraindicated).

2. Indications for Empiric Gram-Positive / Anti-MRSA Coverage

The routine addition of vancomycin, daptomycin, or linezolid to initial empiric therapy is not recommended. Clinical trials have shown that empiric vancomycin does not improve survival or time to defervescence, while increasing nephrotoxicity and VRE emergence.

• Empiric Vancomycin (15–20 mg/kg IV q8–12h) is indicated ONLY if one of the following criteria is met:
  1. Hemodynamic instability or signs of septic shock.
  2. Suspected catheter-related bloodstream infection (purulence, erythema, or tenderness along the subcutaneous tunnel or exit site).
  3. Clinically evident skin or soft tissue infection.
  4. Radiographically documented pneumonia.
  5. Severe oral mucositis (which predisposes to bacteremia caused by viridans group streptococci, such as Streptococcus mitis, capable of causing life-threatening toxic shock-like syndrome).
  6. Known colonization with MRSA or penicillin-resistant S. pneumoniae.
• De-escalation Rule: If blood cultures show no growth of Gram-positive organisms at 48 to 72 hours, vancomycin should be promptly discontinued, even if the patient remains febrile.

Persistent Fever and Empiric Antifungal Therapy

Most patients defervesce within 3 to 5 days of starting appropriate broad-spectrum antibacterial therapy. If fever persists or recrudesces after 4 to 7 days of broad-spectrum antibacterials and the patient is anticipated to have prolonged neutropenia (> 7 days):

• Etiology: Invasive fungal infections (IFIs), particularly mold infections (Aspergillus fumigatus, Aspergillus flavus, Mucorales, Fusarium) or candidiasis.
• Diagnostic Workup: Serum galactomannan assay, 1,3-beta-D-glucan assay, high-resolution chest CT (evaluating for macronodules with halo sign, wedge-shaped consolidations, or cavitary air-crescent signs), and sinuses CT.
• Empiric / Preemptive Antifungal Selection:
  • Liposomal Amphotericin B: 3 to 5 mg/kg IV once daily. Broadest fungicidal spectrum; covers Candida, Aspergillus, Mucorales, and endemic fungi.
  • Voriconazole: Loading dose 6 mg/kg IV q12h for 2 doses, then 4 mg/kg IV q12h (or 200 mg PO BID). Preferred agent for proven/suspected invasive aspergillosis; inactive against Mucorales. Requires therapeutic drug monitoring (target trough 1.5–5.0 mcg/mL).
  • Isavuconazonium Sulfate (Isavuconazole): 372 mg IV/PO q8h for 6 doses (loading), then 372 mg IV/PO once daily. Active against both Aspergillus and Mucorales; does not prolong the QTc interval (causes QTc shortening); excellent tolerability.
  • Caspofungin: Loading dose 70 mg IV Day 1, then 50 mg IV daily. Effective for Candida and Aspergillus; lacks activity against Mucorales and Cryptococcus.
  • Note on Prior Prophylaxis: If a patient develops persistent febrile neutropenia while already receiving mold-active prophylaxis (e.g., posaconazole oral suspension or delayed-release tablets), switching to a different antifungal class (e.g., liposomal amphotericin B) is indicated pending diagnostic bronchoscopy and galactomannan testing.