Invasive Fungal Infections

Learning Objectives

Upon completion of this chapter, learners will be able to:

Describe the epidemiology and risk factors for invasive candidiasis, cryptococcosis, aspergillosis, and mucormycosis
Identify key clinical presentations and diagnostic approaches for each major invasive fungal infection
Select appropriate antifungal therapy based on patient factors, fungal species, and infection site
Recognize antifungal drug toxicities and their management
Apply evidence-based treatment guidelines to clinical scenarios

1 Introduction to Invasive Fungal Infections

1.1 The Global Burden of Fungal Disease

Invasive fungal infections (IFIs) represent a significant and growing threat to global health. While often overlooked compared to bacterial and viral pathogens, fungi cause substantial morbidity and mortality, particularly among immunocompromised populations [1].

Key Statistics

Over 1 million deaths annually from invasive fungal infections worldwide
Fungal infections kill more people than malaria and are equivalent to tuberculosis deaths
The burden is likely underestimated due to diagnostic challenges

Global distribution of invasive fungal disease mortality. Deaths from major fungal pathogens are dramatically underreported, particularly in resource-limited settings where diagnostic capacity is limited.

1.2 Spectrum of Fungal Diseases

Fungal infections can be categorized by their anatomical involvement and host immune status:

Table 1: Classification of Mycoses

Type	Location	Examples	Primary Hosts
Superficial mycoses	Epidermis, hair, nails	Dermatophytosis, pityriasis	Immunocompetent
Subcutaneous mycoses	Dermis, subcutaneous tissue	Sporotrichosis, chromoblastomycosis	Immunocompetent (trauma)
Systemic mycoses from primary pathogens	Deep organs	Histoplasmosis, coccidioidomycosis	Immunocompetent & compromised
Systemic mycoses from opportunistic pathogens	Deep organs	Candidiasis, aspergillosis, cryptococcosis	Immunocompromised

Spectrum of fungal diseases, ranging from superficial infections (skin and nails) to life-threatening systemic mycoses in immunocompromised hosts.

1.3 WHO Fungal Priority Pathogens List (2022)

The World Health Organization released its first fungal priority pathogens list in 2022, categorizing fungi by public health importance [2]:

WHO Priority Groups

Critical Priority:

Cryptococcus neoformans
Candida auris
Aspergillus fumigatus
Candida albicans

High Priority:

Nakaseomyces glabrata (formerly Candida glabrata)
Histoplasma spp.
Eumycetoma causative agents
Mucorales
Fusarium spp.
Candida tropicalis
Candida parapsilosis

Medium Priority:

Scedosporium spp.
Lomentospora prolificans
Coccidioides spp.
Pichia kudriavzevii (formerly Candida krusei)
Cryptococcus gattii
Talaromyces marneffei
Pneumocystis jirovecii
Paracoccidioides spp.

2 Antifungal Therapies

2.1 Evolution of Antifungal Development

The development of systemic antifungal agents has progressed significantly since the introduction of amphotericin B in 1958:

Table 2: Timeline of Antifungal Development

Era	Year(s)	Agents	Target
Early	1958	Amphotericin B deoxycholate	Ergosterol binding
Azole development	1981-1992	Ketoconazole, fluconazole, itraconazole	Lanosterol 14-α-demethylase
Lipid formulations	1990s	L-AMB, ABLC, ABCD	Ergosterol (reduced toxicity)
Expanded-spectrum azoles	2002-2015	Voriconazole, posaconazole, isavuconazole	Lanosterol 14-α-demethylase
Echinocandins	2001-2006	Caspofungin, micafungin, anidulafungin	β-1,3-glucan synthase
Novel agents	2023+	Ibrexafungerp, rezafungin, olorofim	Various new targets

Timeline of systemic antifungal drug development from amphotericin B (1958) through contemporary novel agents.

2.2 Mechanisms of Action

Antifungal agents target distinct components of the fungal cell:

Cell Membrane Targets:

Polyenes (amphotericin B): Bind ergosterol, creating pores that lead to cell death
Azoles: Inhibit lanosterol 14-α-demethylase (CYP51), disrupting ergosterol synthesis

Cell Wall Targets:

Echinocandins: Inhibit β-1,3-glucan synthase, disrupting cell wall integrity

Antifungal mechanisms of action, showing primary targets on the fungal cell membrane (ergosterol) and cell wall (β-1,3-glucan).

2.3 Antifungal Spectrum of Activity

The spectrum of activity varies significantly across drug classes. Selecting the appropriate agent requires matching the likely or confirmed pathogen against coverage gaps:

Table 3: Antifungal Spectrum of Activity

Agent	Candida	Aspergillus	Cryptococcus	Mucorales
Fluconazole	++	−	++	−
Voriconazole	+++	+++	+	−
Posaconazole	+++	+++	+	++
Isavuconazole	+++	+++	+	++
Echinocandins	+++	++	−	−
Amphotericin B	+++	++	+++	+++

Clinical Pearl

The spectrum of antifungal activity varies significantly between drug classes:

Fluconazole: Most Candida spp. (not C. krusei, reduced activity vs C. glabrata); no mold activity
Voriconazole/Isavuconazole/Posaconazole: Broad Candida coverage + Aspergillus; posaconazole and isavuconazole have Mucorales activity
Echinocandins: Candida spp. (including C. glabrata) + Aspergillus; no Cryptococcus or Mucorales activity
Amphotericin B: Broadest spectrum - most yeasts and molds including Mucorales

2.4 Antifungal Tissue Distribution

Understanding antifungal tissue penetration is critical for selecting appropriate therapy [3]:

Table 4: Antifungal Tissue Penetration

Drug	CSF	Eye/Vitreous	Urine	Lung ELF
Fluconazole	+++	+++	+++	++
Voriconazole	++	++	+	+++
Posaconazole	+	+	-	+++
Isavuconazole	+	+	-	+++
Amphotericin B	+/-	+/-	+	++
Echinocandins	-	-	-	+

Important Consideration

Echinocandins have poor CNS, eye, and urine penetration. They should not be used as monotherapy for infections at these sites.

3 Invasive Candidiasis

3.1 Epidemiology

Invasive candidiasis is the most common invasive fungal infection in hospitalized patients. The epidemiology has evolved significantly over recent decades [4]:

Species Distribution:

Candida albicans: 40-60% (decreasing)
Candida glabrata: 15-25% (increasing, especially with azole exposure)
Candida parapsilosis: 10-20% (associated with central lines, TPN)
Candida tropicalis: 5-10% (more common in neutropenic patients)
Candida krusei: 2-5% (intrinsically fluconazole-resistant)
Candida auris: Emerging multidrug-resistant threat

3.2 Risk Factors

Major Risk Factors for Invasive Candidiasis

Host Factors:

Neutropenia
Diabetes mellitus
Extremes of age
Recent surgery (especially abdominal)
Burns

Healthcare Exposures:

Central venous catheters
Total parenteral nutrition
Broad-spectrum antibiotics
ICU admission >3 days
Prior colonization with Candida

Medications:

Corticosteroids
Immunosuppressive agents
Prior antifungal exposure

3.3 Pathogenesis

Candida species are commensal organisms of the human gastrointestinal tract, skin, and mucous membranes. Invasive disease occurs when host defenses are compromised or mucosal barriers are breached.

Key Pathogenic Steps:

Colonization of mucosal surfaces
Breach of mucosal barrier (surgery, mucositis, catheters)
Bloodstream invasion
Dissemination to deep organs
Biofilm formation (especially on devices)

Pathogenesis of invasive candidiasis. Disruption of mucosal barriers (e.g., by surgery, chemotherapy-induced mucositis, or catheters) allows *Candida* to translocate from commensal sites to the bloodstream and deep organs. Biofilm formation on intravascular devices further complicates treatment.

3.4 Clinical Presentations

Candidemia:

Fever unresponsive to antibiotics
Often no localizing signs
May have metastatic complications (endophthalmitis, osteomyelitis, endocarditis)

Deep-seated Candidiasis:

Hepatosplenic candidiasis (chronic disseminated): Fever, elevated alkaline phosphatase, target lesions on imaging
Candida peritonitis: Abdominal surgery, peritoneal dialysis
Candida endocarditis: Prosthetic valves, IV drug use

Hepatosplenic (chronic disseminated) candidiasis. Characteristic “bull’s eye” target lesions visible on CT/MRI, typically appearing as neutrophil counts recover following chemotherapy-induced neutropenia.

3.5 Diagnosis

The “Missing 50%”

Blood cultures detect only approximately 50% of invasive candidiasis cases, highlighting the need for adjunctive diagnostic methods [5].

Culture-Based Methods:

Blood cultures: Gold standard but limited sensitivity
Tissue cultures: Higher yield but require invasive sampling

Non-Culture Diagnostics:

Table 5: Non-Culture Diagnostics for Invasive Candidiasis

Test	Sensitivity	Specificity	Comments
β-D-glucan	75-80%	80%	Pan-fungal; false positives with dialysis, gauze, some antibiotics
T2Candida Panel	91%	99%	Direct from blood; rapid results; detects 5 common species
Candida PCR	85-95%	90-95%	Not widely standardized

Histopathology:

Tissue diagnosis of invasive candidiasis relies on special stains to highlight fungal elements in tissue specimens:

Stain	Appearance
PAS (Periodic Acid–Schiff)	Magenta yeast and pseudohyphae
GMS (Gomori Methenamine Silver)	Black yeast and hyphae against green background

Histopathology of invasive candidiasis. Left: PAS stain showing magenta-staining yeast and pseudohyphae in tissue. Right: GMS stain highlighting black fungal elements against a green counterstain.

3.6 Treatment

3.6.1 Initial Therapy

Treatment selection depends on patient stability, prior azole exposure, and suspected species [6]:

flowchart TD
    A[Candidemia Suspected/Confirmed] --> B{Patient Status}
    B -->|Hemodynamically Stable| C{Prior Azole Exposure?}
    B -->|Unstable/Severe| D[Echinocandin]
    C -->|No| E[Fluconazole 800mg load, then 400mg daily]
    C -->|Yes| D
    D --> F{Species Identification}
    F -->|C. glabrata| G[Continue Echinocandin]
    F -->|C. krusei| G
    F -->|C. parapsilosis| H[Consider Fluconazole]
    F -->|Other susceptible| I[Step-down to Fluconazole if stable]

Figure 1: Treatment Algorithm for Candidemia

3.6.2 Source Control

Critical Intervention

Central venous catheter removal is associated with improved outcomes and should be performed whenever feasible in patients with candidemia.

3.6.3 Duration of Therapy

Uncomplicated candidemia: 14 days after first negative blood culture and resolution of symptoms
Deep-seated infection: Extended duration based on site (e.g., endocarditis: 6 weeks post-valve surgery)

3.6.4 Ophthalmologic Examination

All patients with candidemia should receive a dilated funduscopic examination to evaluate for endophthalmitis:

Timing: Within 1 week of diagnosis (after neutrophil recovery in neutropenic patients)
Finding: Chorioretinal lesions with or without vitritis
Management: Extended antifungal therapy; ophthalmology consultation

Funduscopic appearance of *Candida* chorioretinitis/endophthalmitis. Cotton-wool exudates and “string of pearls” lesions in the vitreous indicate ocular involvement, which occurs in 10–15% of candidemia cases and requires prompt ophthalmology consultation. Note that echinocandins do not penetrate the vitreous — fluconazole or voriconazole is required for ocular disease.

3.7 Antifungal Susceptibility Testing

Susceptibility testing is recommended for all bloodstream isolates. CLSI and EUCAST breakpoints guide interpretation:

Table 6: CLSI Breakpoints for Candida Species (mg/L)

Species	Fluconazole	Echinocandins	Comments
C. albicans	S ≤2	S ≤0.25	Usually susceptible
C. glabrata	SDD ≤32	S ≤0.12	Dose-dependent; check echinocandin susceptibility
C. krusei	R (intrinsic)	S ≤0.25	Use echinocandin or amphotericin B
C. parapsilosis	S ≤2	Higher MICs (S ≤2)	Fluconazole often preferred
C. auris	Often R	Variable	Requires individualized testing

4 Cryptococcosis

4.1 Epidemiology

Cryptococcosis is caused by encapsulated yeasts of the Cryptococcus species complex. It remains a leading cause of mortality in HIV-infected individuals, particularly in resource-limited settings [7,8].

Global Burden:

Approximately 220,000 cases of cryptococcal meningitis annually
180,000 deaths per year
Most cases occur in sub-Saharan Africa
Leading cause of meningitis in adults with HIV in Africa

Global distribution of cryptococcal meningitis. Sub-Saharan Africa bears the greatest burden, where *Cryptococcus neoformans* is a leading cause of meningitis-related mortality in HIV-infected individuals. The incidence has declined substantially in settings with widespread antiretroviral therapy access.

4.2 Species and Ecology

Table 7: Cryptococcus Species Characteristics

Species	Primary Host	Geographic Distribution	Clinical Association
C. neoformans	Immunocompromised (HIV, transplant)	Worldwide	Soil, bird droppings
C. gattii	Immunocompetent & immunocompromised	Pacific Northwest, Australia, tropics	Eucalyptus trees

4.3 Pathogenesis

Cryptococcus has several virulence factors that enable evasion of host defenses:

Polysaccharide capsule: Antiphagocytic; immunomodulatory
Melanin production: Antioxidant protection
Ability to survive within macrophages: Trojan horse mechanism for CNS penetration
Titan cells: Large cells resistant to phagocytosis

India ink preparation of cerebrospinal fluid showing encapsulated *Cryptococcus* yeast. The prominent polysaccharide capsule (visible as a clear halo surrounding the yeast cell) prevents phagocytosis and is the organism’s primary virulence factor.

4.4 Clinical Manifestations

Cryptococcal Meningitis:

Subacute presentation over 1-2 weeks
Headache (most common)
Fever
Altered mental status
Neck stiffness (less common than bacterial meningitis)
Cranial nerve palsies
Visual disturbances

Elevated Intracranial Pressure

Elevated intracranial pressure (ICP) is a major cause of morbidity and mortality in cryptococcal meningitis. Opening pressure >25 cm H₂O is associated with poor outcomes.

Pulmonary Cryptococcosis:

May be asymptomatic (incidental finding)
Cough, dyspnea, chest pain
Nodules or infiltrates on imaging

Disseminated Disease:

Skin lesions (umbilicated papules resembling molluscum)
Bone involvement
Prostate (sanctuary site)

Cryptococcal skin lesions. Papulonodular umbilicated lesions on the neck and upper trunk can mimic molluscum contagiosum. Skin involvement indicates disseminated cryptococcosis and should prompt full evaluation including lumbar puncture.

4.5 Diagnosis

Lumbar Puncture Findings:

Table 8: CSF Findings in Cryptococcal Meningitis

Parameter	Typical Finding
Opening pressure	Elevated (often >25 cm H₂O)
WBC	Elevated (lymphocyte predominant); may be low in severe immunosuppression
Glucose	Low
Protein	Elevated
CrAg (LFA)	Positive
India ink	Positive in ~75–85% of cases

Elevated Opening Pressure

Opening pressure must always be measured and documented. Severely immunosuppressed patients may have a paradoxically low WBC despite high fungal burden — this portends a worse prognosis. ICP management is often more critical than antifungal drug choice in the first days of treatment.

Diagnostic Tests:

Table 9: Diagnostic Tests for Cryptococcosis

Test	Sensitivity	Specificity	Comments
CSF CrAg (lateral flow)	99%	99%	Rapid, point-of-care
Serum CrAg	99%	99%	Can be positive before symptoms
CSF India ink	75-85%	>95%	Visualizes capsule; less sensitive
CSF culture	95%	100%	Gold standard; takes 3-7 days

Screening Recommendation

Serum cryptococcal antigen (CrAg) screening is recommended for HIV-infected individuals with CD4 <100 cells/μL to identify subclinical disease before symptom onset.

Point-of-care lateral flow assay (LFA) for cryptococcal antigen (CrAg). This rapid, inexpensive, highly accurate test (sensitivity and specificity ~99%) has transformed early diagnosis, particularly in resource-limited settings. A positive serum CrAg can precede clinical symptoms and should prompt lumbar puncture to evaluate for CNS involvement.

4.6 Treatment

4.6.1 The AMBITION Trial

The AMBITION trial established single high-dose liposomal amphotericin B as the preferred induction regimen [9]:

Key Findings:

Single dose L-AMB (10 mg/kg) + 14 days flucytosine + fluconazole was non-inferior to 7-day amphotericin B deoxycholate regimens
10-week mortality: 24.8% vs 28.7% (difference -3.9%, 95% CI -10.4 to 2.6)
Fewer adverse events with single-dose regimen
Simplified administration

4.6.2 Treatment Regimens

Table 10: Cryptococcal Meningitis Treatment Phases

	Induction (2 weeks)	Consolidation (8 weeks)	Maintenance
Preferred	L-AMB 10 mg/kg × 1 dose + flucytosine 100 mg/kg/day × 14 days + fluconazole 1200 mg/day × 14 days	Fluconazole 800 mg/day	Fluconazole 200 mg/day
Alternative	AmB deoxycholate 1 mg/kg/day × 7 days + flucytosine × 7 days	—	—
Discontinue	—	—	CD4 >100 cells/μL for ≥3 months on ART

Induction (2 weeks):

Preferred: Single dose liposomal amphotericin B (10 mg/kg) + flucytosine (100 mg/kg/day) + fluconazole (1200 mg/day)
Alternative: Amphotericin B deoxycholate (1 mg/kg/day) + flucytosine (100 mg/kg/day) × 7 days

Consolidation (8 weeks):

Fluconazole 800 mg/day

Maintenance:

Fluconazole 200 mg/day until immune reconstitution (CD4 >100 for 3 months on ART)

4.6.3 Management of Elevated ICP

Critical Intervention

Aggressive management of elevated intracranial pressure is essential for survival. Therapeutic lumbar punctures should be performed to reduce opening pressure by 50% or to <20 cm H₂O.

Approach:

Daily lumbar punctures initially if opening pressure >25 cm H₂O
Remove sufficient CSF to reduce pressure by 50% or to normal
Consider lumbar drain or VP shunt for refractory cases
Avoid corticosteroids (associated with worse outcomes)
Acetazolamide and mannitol are not effective

4.7 Prognosis

Factors associated with poor outcome [10]:

High CSF fungal burden
Altered mental status at presentation
Elevated opening pressure
Low CSF white cell count
Underlying malignancy
Inadequate ICP management

5 Invasive Aspergillosis

5.1 Spectrum of Aspergillus Diseases

The clinical manifestations of Aspergillus infection depend on host immune status:

Spectrum of *Aspergillus* disease, illustrating how host immune status determines clinical presentation. Immunocompromised patients develop invasive disease (left), patients with structural lung disease develop aspergillomas (center), and those with immune hyperreactivity develop allergic syndromes (right).

Immunocompromised Hosts (Immune Dysfunction):

Acute invasive aspergillosis
Subacute invasive aspergillosis

Normal Immune Function (Middle of Spectrum):

Tracheobronchitis
Aspergilloma
Chronic cavitary aspergillosis
Chronic fibrosing aspergillosis

Immune Hyperactivity:

Allergic bronchopulmonary aspergillosis (ABPA)
Allergic fungal sinusitis

5.2 Aspergillus Species

Table 11: Common Aspergillus Species

Species	Frequency	Clinical Significance
A. fumigatus	70-80%	Most common cause of IA
A. flavus	10-15%	More common in sinusitis; produces aflatoxins
A. niger	5-10%	Otomycosis; may produce aspergillomas
A. terreus	2-5%	Intrinsically amphotericin B resistant
A. nidulans	Rare	Associated with chronic granulomatous disease

5.3 Mode of Acquisition

Aspergillus conidia (2-3 μm) are ubiquitous in the environment and inhaled daily. In immunocompetent hosts, conidia are cleared by:

Mucociliary clearance
Alveolar macrophage phagocytosis
Neutrophil killing of germinating hyphae

5.4 Risk Factors

Major Risk Factors for Invasive Aspergillosis

Host Factors:

Severe and prolonged neutropenia (≥3 weeks)
Hematopoietic stem cell transplant (especially allogeneic)
Solid organ transplant (especially lung)
Chronic granulomatous disease
Advanced AIDS

Iatrogenic:

High-dose corticosteroids (≥0.5 mg/kg/day prednisone equivalent)
Ibrutinib and other BTK inhibitors
T-cell depleting therapies

Emerging Risk Groups:

COPD with corticosteroid therapy
ICU patients (especially with influenza or COVID-19)
Liver cirrhosis

5.5 Pathogenesis

5.5.1 Bronchial-Alveolar Phase

Initial invasion occurs through bronchial and alveolar walls:

Conidia germinate in airways
Hyphae invade bronchial/alveolar epithelium
Associated inflammation
CT findings: Centrilobular nodules, tree-in-bud pattern
Low fungal burden; serum galactomannan often negative
BAL galactomannan/culture may be positive

5.5.2 Angioinvasive Phase

In severely immunocompromised patients, disease progresses to angioinvasion:

Progression Timeline:

Table 12: Temporal Progression of Angioinvasive Aspergillosis

Day	Pathology	CT Finding	Biomarkers
0-3	Hyphal tissue invasion	Macronodule ± halo sign	GM may be negative
5-7	Hemorrhage, infarction	Dense consolidation	Serum GM positive
10-12	Extensive necrosis	Hypodense sign	High fungal burden
15-18	Neutrophil recovery, cavitation	Air-crescent sign	May persist

5.6 Clinical Presentation

Pulmonary Aspergillosis:

Fever unresponsive to antibiotics
Pleuritic chest pain
Cough, hemoptysis
Dyspnea

Sinus Aspergillosis:

Facial pain
Nasal congestion/discharge
Periorbital swelling
Black eschar on nasal examination

Disseminated Aspergillosis:

CNS involvement (ring-enhancing lesions, abscesses)
Cutaneous lesions
Multiple organ involvement

5.7 Diagnosis

5.7.1 Imaging

CT Findings Suggestive of IPA:

Nodules with halo sign (ground-glass surrounding dense core)
Air-crescent sign (late finding with neutrophil recovery)
Wedge-shaped infiltrates
Cavitation

Halo Sign

The halo sign (ground-glass attenuation surrounding a nodule) is relatively specific for angioinvasive mold infection in neutropenic patients, particularly in the first week of infection.

CT Pulmonary Angiography (Vessel Occlusion Sign):

Can help differentiate IPA from other pulmonary processes
Positive VOS shows vessel truncation within or adjacent to nodules

5.7.2 Laboratory Diagnosis

Culture and Histopathology:

BAL culture: Sensitivity 50-60%
Tissue biopsy: Septate hyphae with acute-angle (45°) branching
PAS and GMS stains highlight fungal elements

Histopathology of invasive aspergillosis. Left: GMS stain in tissue showing dichotomously branching septate hyphae with characteristic 45° (acute-angle) branching. Right: Calcofluor white stain on BAL specimen highlighting hyphal elements under fluorescence microscopy.

Galactomannan Testing:

Table 13: Galactomannan Testing Performance

Sample	Cutoff	Sensitivity	Specificity	Notes
Serum	≥0.5 ODI	70-80%	85-90%	Better in neutropenic patients
BAL	≥1.0 ODI	85-90%	90-95%	Higher sensitivity than serum

False Positives

Galactomannan false positives can occur with:

Piperacillin-tazobactam (older formulations)
Mucositis
Certain foods
Cross-reactivity with other fungi (Fusarium, Histoplasma)

Other Biomarkers:

β-D-glucan: Less specific (pan-fungal); may be useful in combination
Aspergillus PCR: High sensitivity; not yet standardized

5.8 Treatment

5.8.1 First-Line Therapy

Triazoles with mold activity are preferred for primary therapy [11]:

If NO Prior Mold-Active Prophylaxis:

Voriconazole (loading: 6 mg/kg IV q12h × 2 doses; maintenance: 4 mg/kg IV q12h or 200-300 mg PO q12h)
Isavuconazole (loading: 200 mg q8h × 6 doses; maintenance: 200 mg daily)
Posaconazole (300 mg IV/PO q12h × 2 doses, then 300 mg daily)

If Receiving Posaconazole Prophylaxis:

Liposomal amphotericin B (3-5 mg/kg/day) initially
Reassess triazole failure: drug levels, resistance, alternative diagnosis
Consider switching to alternative triazole if isolate is susceptible and patient stabilizes

5.8.2 Antifungal Resistance

Triazole resistance in Aspergillus fumigatus is an emerging concern:

Azole Resistance

Environmental azole resistance (TR34/L98H and TR46/Y121F/T289A mutations) is increasing globally due to agricultural fungicide use. Rates vary by region:

Netherlands: 5-15%
UK: 5-10%
Germany: 3-5%
United States: 1-3%
Some Asian regions: Up to 30%

Consider resistance testing in refractory cases or high-prevalence regions.

5.8.3 Duration

Minimum: 6-12 weeks
Continue until: Resolution of all lesions, reversal of immunosuppression
Secondary prophylaxis: Consider during subsequent immunosuppression

5.9 Prognosis

Key prognostic factors:

Early diagnosis and prompt antifungal therapy
Recovery from neutropenia/immune suppression
Underlying disease status
Site of infection (CNS involvement = worse prognosis)
Triazole resistance

6 Other Mold Infections

6.1 Fusariosis

Fusarium species are emerging pathogens causing severe infections in neutropenic patients.

Key Features:

Most common scenario: Persistent neutropenia
Common species: F. solani complex (50%), F. oxysporum (14%), F. verticillioides (10-11%)
Characteristic finding: Metastatic skin lesions
Positive blood cultures in 30-50% of cases (unlike other mold infections)
Macroconidia are classic (banana-shaped)

Breakthrough *Fusarium* infection during neutropenia. Unlike most invasive mold infections, *Fusarium* frequently produces positive blood cultures. Characteristic banana-shaped macroconidia are visible on microscopy. Metastatic necrotic skin lesions (ecthyma gangrenosum-like) and ocular involvement are distinctive features not typically seen with aspergillosis.

Metastatic skin, ocular, and CNS lesions of disseminated fusariosis. These necrotic cutaneous lesions can mimic ecthyma gangrenosum from *Pseudomonas* infection. CNS involvement carries a particularly poor prognosis, especially in the absence of neutrophil recovery.

Treatment:

High-dose liposomal amphotericin B ± voriconazole
Neutrophil recovery is critical
G-CSF may be beneficial

Fusarium Outbreak

A multinational outbreak (185 exposed, 9 cases) of nosocomial Fusarium solani meningitis occurred among immunocompetent patients who underwent surgery with epidural anesthesia in Mexico in 2023 [12]. The pathogen showed high predilection for the brainstem and vertebrobasilar arterial system, with high mortality from vessel injury.

Epidemiological map of the 2023 multinational nosocomial *Fusarium solani* meningitis outbreak, linked to contaminated surgical/anesthesia equipment. This outbreak highlights the risk of invasive fungal infections in immunocompetent patients following breaches in sterile technique. [12]

6.2 Mucormycosis

6.2.1 Epidemiology and Risk Factors

Mucormycosis is caused by fungi of the order Mucorales, including Rhizopus, Mucor, Lichtheimia, and others.

Ecology and morphology of Mucorales. These ubiquitous environmental saprophytes are found in soil and decaying organic matter. Characteristic features include large, ribbon-like, pauciseptate hyphae with right-angle branching — distinguishing them from the septate, acute-angle-branching hyphae of *Aspergillus*.

Risk Factors:

Uncontrolled diabetes mellitus (especially ketoacidosis)
Hematologic malignancy with neutropenia
Hematopoietic stem cell transplant
Solid organ transplant
Iron overload states
Deferoxamine therapy (acts as a siderophore)
Trauma, burns
COVID-19 (especially in India, 2021 outbreak)

6.2.2 Common Species

Table 14: Common Mucorales Species

Genus	Clinical Significance
Rhizopus spp.	Most common (especially R. arrhizus)
Mucor spp.	Less common but significant
Lichtheimia spp.	Common in immunocompromised
Rhizomucor spp.	More aggressive disease
Cunninghamella spp.	Disseminated disease; very poor prognosis
Apophysomyces spp.	Cutaneous/soft tissue (trauma)

6.2.3 Pathogenesis

Mucorales have a unique relationship with iron:

Spores inhaled, deposited in nasal turbinates or alveoli
Macrophages attempt phagocytosis (impaired by glucocorticoids)
Neutrophils damage hyphal forms; iron acquisition supports proliferation
Angioinvasion leads to thrombosis, hemorrhage, and tissue necrosis
Hyperglycemia, acidosis, and free iron facilitate growth

Pathogenesis of mucormycosis. The interplay of metabolic factors (hyperglycemia, acidosis, iron overload) and immune defects (impaired macrophage and neutrophil function) creates the conditions for spore germination, angioinvasion, and rapid tissue destruction.

Deferoxamine Risk

Iron chelation with deferoxamine increases mucormycosis risk (fungus uses it as a xenosiderophore). Newer chelating agents like deferasirox do not carry this risk.

6.2.4 Clinical Manifestations

Rhinocerebral Mucormycosis:

Most common form in diabetic patients
Begins with sinusitis, facial pain
Rapid progression with necrotic eschar (black eschar = late finding)
Orbital involvement: Proptosis, vision loss
Cavernous sinus thrombosis
CNS extension: High mortality

Pulmonary Mucormycosis:

More common in neutropenic patients
Nodular infiltrates
Reverse halo sign
Pleural effusions
Rapid progression

Cutaneous Mucormycosis:

Trauma, burns, surgical wounds
Natural disasters (e.g., Joplin tornado)
Combat injuries
Necrotizing soft tissue infection

6.2.5 Diagnosis

Diagnostic Limitations

Serum β-D-glucan and galactomannan do NOT detect Mucorales. These tests being negative does not exclude mucormycosis.

Diagnostic Approach:

Histopathology: Wide (6-16 μm), ribbon-like, pauciseptate hyphae with right-angle branching
Culture: Rapid growth (“lid lifter”); confirm species identification
PCR/sequencing: Available in some centers
MALDI-TOF: For isolate identification

Imaging:

MRI: “Black turbinate sign” (devitalized tissue in sinuses)
CT: Reverse halo sign in pulmonary disease

MRI “black turbinate sign” in rhinocerebral mucormycosis. Loss of contrast enhancement of the turbinates indicates devitalized, infarcted tissue — a highly specific finding in the appropriate clinical context. MRI is more sensitive than CT for early tissue invasion; a normal CT should not provide false reassurance in a high-risk patient.

Reverse halo sign on CT in pulmonary mucormycosis. In contrast to the aspergillosis halo sign (dense nodule surrounded by ground-glass), the reverse halo shows ground-glass opacity *surrounded* by a rim of consolidation. This finding is relatively specific for pulmonary mucormycosis in the appropriate clinical setting.

6.2.6 Treatment

Principles:

Surgical debridement: Essential; often requires multiple operations
Reversal of predisposing conditions: Glucose control, reduce immunosuppression
Antifungal therapy: Start immediately

Radical surgical debridement for rhinocerebral mucormycosis. While often disfiguring, aggressive surgery removing all necrotic tissue is associated with significantly improved survival. Facial prosthetics and reconstructive surgery can be pursued after the infection is cured. Do not delay surgery awaiting culture results in high-risk patients.

Antifungal Regimen:

Initial: Liposomal amphotericin B 5-10 mg/kg/day
Step-down: Posaconazole or isavuconazole (for patients responding or with toxicity)
Duration: Prolonged; minimum until clinical/radiographic resolution

Treatment Pearls

Higher doses of L-AMB (10 mg/kg/day) may be considered for CNS involvement
Combination therapy (L-AMB + posaconazole/isavuconazole) is sometimes used but not proven superior
Surgical debridement should not be delayed for imaging; early aggressive surgery improves outcomes

6.2.7 Prognosis

Mucormycosis carries significant morbidity and mortality:

Overall mortality: 40-80% depending on form and host
Rhinocerebral with CNS extension: >80% mortality
Disseminated disease: >90% mortality
Factors improving survival: Early diagnosis, surgical debridement, immune recovery

Healthcare Professional Survey

In a Twitter poll of 1,885 infectious disease specialists, 44% rated mucormycosis as the “scariest” infectious disease, more than Candida auris (18%), Staphylococcus aureus (24%), or SARS-CoV-2 (14%).

7 Antifungal Toxicities

7.1 Amphotericin B Toxicities

7.1.1 Nephrotoxicity

Amphotericin B deoxycholate causes significant nephrotoxicity through multiple mechanisms:

Afferent arteriole constriction: Reduced renal blood flow
Tubuloglomerular feedback: Further vasoconstriction
Direct tubular toxicity: LDL-bound AMB accumulates via LDL receptors
Electrolyte wasting: K⁺, Mg²⁺, Na⁺ loss

Mechanism of amphotericin B nephrotoxicity. Afferent arteriolar vasoconstriction reduces renal blood flow, while LDL-mediated drug accumulation in tubular cells causes direct damage and electrolyte wasting. Understanding this mechanism helps guide monitoring (creatinine, potassium, magnesium) and underscores the advantage of liposomal formulations.

Clinical Impact:

≥2-fold increase in serum creatinine in 26% of patients receiving AMB deoxycholate
Severe electrolyte abnormalities common

7.1.2 Liposomal Formulation Advantages

Liposomal amphotericin B reduces nephrotoxicity:

Liposomes do not undergo glomerular filtration
Reduced binding to LDL receptors
≥2-fold SCr increase in only 10% of patients
Allows higher dosing when needed

7.2 Triazole Toxicities

Table 15: Triazole-Specific Toxicities

Toxicity	Most Commonly Associated Agent(s)
Hepatotoxicity	All azoles (highest with voriconazole)
QTc prolongation	All azoles (less with isavuconazole)
Visual disturbances (photopsia)	Voriconazole
Phototoxicity/skin cancer	Voriconazole (long-term)
CNS effects (hallucinations)	Voriconazole
Peripheral neuropathy	Itraconazole > voriconazole > others
GI intolerance	Itraconazole, posaconazole
Cardiomyopathy	Itraconazole
Periostitis (bone pain)	Voriconazole (fluoride toxicity)
Adrenal suppression	Itraconazole, posaconazole

Monitoring Recommendations

Liver function tests at baseline and periodically during therapy
Trough drug levels for voriconazole (target 1-5 μg/mL), posaconazole (>1 μg/mL), and isavuconazole (if concerns about efficacy/toxicity)
ECG at baseline if risk factors for QTc prolongation
Visual symptoms inquiry for voriconazole patients

8 Summary and Key Points

Take-Home Messages

Invasive Candidiasis:

Blood cultures miss 50% of cases; use adjunctive diagnostics
Source control (catheter removal) improves outcomes
Echinocandins are first-line for unstable patients
Dilated eye exam for all patients with candidemia

Cryptococcosis:

CrAg screening for HIV patients with CD4 <100
Single high-dose L-AMB (AMBITION regimen) is preferred
Aggressive ICP management is critical
Avoid corticosteroids

Invasive Aspergillosis:

Early CT and galactomannan testing in high-risk patients
Voriconazole, isavuconazole, or posaconazole for primary therapy
Use L-AMB if breakthrough on azole prophylaxis
Monitor for azole resistance

Mucormycosis:

β-D-glucan and galactomannan do NOT detect Mucorales
Surgical debridement is essential
High-dose liposomal amphotericin B (5-10 mg/kg/day)
Control underlying conditions (diabetes, immunosuppression)

Appendix: Quick Reference Tables

Antifungal Dosing Reference

Table 16: Antifungal Dosing Quick Reference

Drug	Loading Dose	Maintenance Dose	Notes
Fluconazole	800 mg	400 mg daily	Dose-adjust for renal impairment
Voriconazole	6 mg/kg IV q12h × 2	4 mg/kg IV q12h or 200–300 mg PO q12h	TDM target: 1–5 μg/mL; avoid IV in renal impairment (cyclodextrin)
Posaconazole DR	300 mg q12h × 2	300 mg daily	Tablet preferred over suspension (better bioavailability)
Isavuconazole	200 mg q8h × 6 doses	200 mg daily	No dose adjustment for renal/hepatic impairment
Caspofungin	70 mg	50 mg daily	Dose-adjust for hepatic impairment
Micafungin	—	100 mg daily	—
Anidulafungin	200 mg	100 mg daily	—
Liposomal AMB	—	3–5 mg/kg daily (mucormycosis: 5–10 mg/kg)	Monitor renal function and electrolytes

Antifungal Drug Interactions

All triazoles are significant CYP450 inhibitors. Dose reductions and/or level monitoring are essential when co-administering with immunosuppressants and other narrow-therapeutic-index drugs.

Table 17: Key Azole Drug Interactions via CYP450

Azole	CYP Inhibition	Key Interactions
Voriconazole	3A4, 2C19, 2C9	Calcineurin inhibitors (↑↑), sirolimus (↑↑↑; often contraindicated), warfarin, phenytoin
Posaconazole	3A4	Calcineurin inhibitors (↑↑), sirolimus (↑↑↑), statins
Isavuconazole	3A4 (moderate)	Calcineurin inhibitors (↑); fewer interactions than voriconazole
Fluconazole	3A4, 2C9	Warfarin (↑↑), calcineurin inhibitors (↑), sulfonylureas

Sirolimus and Voriconazole

Voriconazole dramatically increases sirolimus levels (often 10-fold or more). This combination is generally avoided; if unavoidable, reduce sirolimus dose by ~90% and monitor levels closely.

References

1.

Brown GD, Denning DW, Gow NAR, Levitz SM, Netea MG, White TC. Hidden killers: Human fungal infections. Science Translational Medicine 2012; 4:165rv13. Available at: https://www.science.org/doi/10.1126/scitranslmed.3004404.

2.

World Health Organization. WHO fungal priority pathogens list to guide research, development and public health action. Geneva: World Health Organization, 2022. Available at: https://www.who.int/publications/i/item/9789240060241.

3.

Felton T, Troke PF, Hope WW. Tissue penetration of antifungal agents. Clinical Microbiology Reviews 2014; 27:68–88. Available at: https://journals.asm.org/doi/10.1128/cmr.00069-13.

4.

Pappas PG, Lionakis MS, Arendrup MC, Ostrosky-Zeichner L, Kullberg BJ. Invasive candidiasis. Nature reviews Disease primers 2018; 4:18026. Available at: http://dx.doi.org/10.1038/nrdp.2018.26.

5.

Clancy CJ, Nguyen MH. Finding the "missing 50%" of invasive candidiasis: How nonculture diagnostics will improve understanding of disease spectrum and transform patient care. Clinical Infectious Diseases 2013; 56:1284–1292. Available at: https://academic.oup.com/cid/article/56/9/1284/404221.

6.

Pappas PG, Kauffman CA, Andes DR, et al. Clinical practice guideline for the management of candidiasis: 2016 update by the infectious diseases society of america. Clinical Infectious Diseases 2016; 62:e1–e50. Available at: https://academic.oup.com/cid/article/62/4/e1/2462830.

7.

Park BJ, Wannemuehler KA, Marston BJ, Govender N, Pappas PG, Chiller TM. Estimation of the current global burden of cryptococcal meningitis among persons living with HIV/AIDS. AIDS 2009; 23:525–530. Available at: https://journals.lww.com/aidsonline/fulltext/2009/02200/estimation_of_the_current_global_burden_of.12.aspx.

8.

Tugume L, Ssebambulidde K, Kasibante J, et al. Cryptococcal meningitis. Nature Reviews Disease Primers 2023; 9:62. Available at: https://www.nature.com/articles/s41572-023-00472-z.

9.

Jarvis JN, Lawrence DS, Meya DB, et al. Single-Dose Liposomal Amphotericin B Treatment for Cryptococcal Meningitis. The New England Journal of Medicine 2022; 386:1109–1120.

10.

Williamson PR, Jarvis JN, Panackal AA, et al. Cryptococcal meningitis: Epidemiology, immunology, diagnosis and therapy. Nature Reviews Neurology 2017; 13:13–24. Available at: https://www.nature.com/articles/nrneurol.2016.167.

11.

Thompson GR, Young J-AH. Aspergillus infections. New England Journal of Medicine 2021; 385:1496–1509. Available at: https://www.nejm.org/doi/full/10.1056/NEJMra2027424.

12.

Strong N, Meeks G, Sheth SA, et al. Neurovascular complications of iatrogenic fusarium solani meningitis. New England Journal of Medicine 2024; 390:522–529. Available at: https://doi.org/10.1056/NEJMoa2308192.