Overview of fungal infections

Last updated: July 20, 2023

Summarytoggle arrow icon

Fungal infections are categorized by the anatomical location of the infection (i.e., as superficial or systemic) and the epidemiological class of the infecting organism (i.e., endemic fungal infection or opportunistic fungal infection). Infections in immunocompetent individuals are generally superficial or limited to the respiratory system. Immunocompromised individuals are susceptible to systemic fungal infections, which are associated with a high risk of mortality. Diagnosing a systemic fungal infection is often difficult because the symptoms are nonspecific and definitive test results may take days to weeks. Suspected systemic fungal infections are usually treated empirically until confirmatory testing is obtained.

See also “General mycology,” “Candidiasis,” “Aspergillosis,” and “Dermatophyte infections.”

Superficial fungal infectionstoggle arrow icon

Overview of the most common cutaneous fungal infections
Pathogen Risk factors Clinical features Diagnostics Treatment
Tinea versicolor (pityriasis versicolor)
  • Hot or humid weather conditions
  • Best initial: KOH showing short hyphae and spores that have a “spaghetti and meatballs” appearance

Superficial mucocutaneous candidiasis

(See also “Opportunistic fungal infections.”)

Systemic fungal infectionstoggle arrow icon

Opportunistic fungal infectionstoggle arrow icon

Overview of the most common opportunistic fungal infections
Pathogen Risk factors Clinical features Diagnostics Treatment
Invasive candidiasis
  • Cryptococcus neoformans
  • AIDS
  • Exposure to pigeon droppings/soil
  • Transmission via inhalation
Pneumocystis pneumonia


  • Imaging
    • Assess the extent of tissue damage and organ involvement
    • Head CT: sinusitis with orbital and intracranial involvement
  • Tissue biopsy (confirmatory): wide-angled branching of irregularly shaped, broad, nonseptate hyphae

Candida, Aspergillus, and Cryptococcus are opportunistic fungal pathogens with low inherent virulence. They commonly cause systemic mycoses in immunocompromised hosts but do not normally affect healthy hosts.

Endemic fungal infectionstoggle arrow icon

Overview of the most common endemic fungal infections
Pathogen Risk factors Clinical features Diagnostics Treatment
  • Histoplasma capsulatum
  • Endemic areas: Mississippi and the Ohio river valley
  • Exposure to bird or bat droppings in endemic areas through activities such as spelunking (cave exploration)
  • Immunosuppression (e.g., AIDS)
Coccidioidomycosis (valley fever)
  • Coccidioides immitis
  • Coccidioides posadasii
  • Travel to Southwestern United States, California
  • Soil/dust exposure in endemic areas (e.g., during windstorms, earthquakes, archeological explorations) [4]
  • Paracoccidioides species
    • Paracoccidioides brasiliensis
    • Paracoccidioides lutzii
  • Travel to South and Central America
  • > [6]
  • KOH/calcofluor staining on smears or silver/PAS-staining on tissue biopsy
    • Budding yeast with “captain's wheel” formation
    • Fungi are identified by comparing their size to that of an RBC (fungal size > RBC)
  • Cultures have low sensitivity.


  • Blastomyces dermatitidis
  • Travel to Southeastern, Central, Eastern, and the Great Lakes region of the United States
  • KOH or culture (confirmatory) of sputum, urine, or body fluids showing:
    • Yeast form (at body temperature or > 37°C): broad-based buds
    • Fungi are identified by comparing their size to that of an RBC (fungal size ≈ RBC)
    • Mold form (at room temperature): circular fungal cells with filamentous hyphae

History of the hidden Ohio and Mississippi river valleys:” Histoplasma is hidden within macrophages and Ohio and Mississippi river valleys are the endemic regions of histoplasma.

Paracoccidiomycosis steers the ship to South and Central America at the captain's wheel: ”Paracoccidiomycosis is endemic in South and Central America and its budding yeast has a captain's wheel appearance.

The yeast form of Blastomycosis forms broad-based buds.

Unlike most other dimorphic fungi, Blastomyces can cause disseminated disease even in immunocompetent hosts.

Other fungal infectionstoggle arrow icon

See also “Mycetoma.”

Sporotrichosis (rose gardener disease)

“A rose gardener plants roses in a pot while smoking a cigar:” sporotrichosis is associated with traumatic gardening injuries, treatment includes potassium iodide, and Sporothrix appears as a cigar-shaped yeast in culture.

Diagnosticstoggle arrow icon

Direct microscopy [9]

  • Evaluation of fungal morphology
  • Usually with KOH
  • Used for preliminary identification

Wood lamp examination [9]

Fungal culture [9]

Histological stains [9]

Others [9]

Management of superficial fungal infectionstoggle arrow icon

Superficial fungal infections refer to those limited to hair, nails, epidermis, and/or mucosa.

Clinical evaluation [10]

Visual inspection of the location, color, shape, and surface characteristics of the lesion may assist in the diagnosis.

Diagnostics [10]

Consider one of the following for diagnostic confirmation:

The diagnosis of a superficial fungal infection is frequently based on visual inspection, but confirmation with diagnostic testing is recommended, especially if systemic treatment is planned. [11][12][13]

Treatment of superficial fungal infections

  • Topical agent dosing rule of thumb: Estimate the required quantity (in grams) using finger-tip units (FTUs). [14]
    • Each FTU can cover an affected body surface area (BSA) equivalent to ∼ 2 closed handprints.
    • 1 g ≈ 2 FTUs, which can cover a BSA of ∼ 4 closed handprints.

Treatment of dermatophyte infections

Oral antifungals can cause hepatotoxicity; LFTs should be monitored. [12][13]

Tinea capitis requires oral treatment. [11]

Treatment of tinea versicolor

Any one of the following:

Mucocutaneous candidiasis

Management of systemic fungal infectionstoggle arrow icon

Clinical evaluation [15][16]

Estimate the probability of the fungal infection type based on history, physical examination, and individual risk factors.

Persistent fever in an immunocompromised patient despite broad-spectrum antibiotic therapy is a common manifestation of a systemic fungal infection. [18]

Risk factors for systemic fungal infection [17][18][19]

Diagnostics [17][20][21]

Obtain rapid antigen testing and imaging while awaiting definitive diagnosis with culture and/or histopathology.

Fungal rapid antigen test [20][21][22]

Rapid antigen tests quickly identify the presence of fungus, but confirmatory studies are typically required to diagnose infection.

Imaging [17][23][24]

Radiologists may be able to provide a preliminary diagnosis of invasive fungal infection based on distinguishing radiographic features if they are aware of the clinical suspicion at the time of imaging. [24]

Confirmatory studies

  • Histopathology (gold standard): evidence of both fungal elements and tissue damage or inflammation [25]
  • Fungal culture (e.g., from blood, respiratory secretions, tissue biopsy, CSF, abscess contents) [21]
    • Identifies species
    • Tests antifungal resistance
    • Limitations

Negative blood cultures do not exclude systemic fungal infection. [23]

Ancillary studies

Treatment with systemic antifungals [30]

Consult infectious diseases for all suspected systemic fungal infections (e.g., fungemia).

Empiric and preemptive [31][32]

Commonly started since culture results can take weeks to return. [21]

Empiric antifungal therapy is the standard of care in patients with neutropenia and persistent fever despite treatment with broad-spectrum antibiotics. [30][36]

Definitive [37]

Depends on the fungal pathogen identified

Aspergillus and Candida are the most common fungal pathogens in patients with febrile neutropenia due to malignancy. [35][36]

Prevention [20][39]

Antifungal prophylaxis (e.g., with posaconazole or micafungin) is indicated for immunocompromised patients with:

Referencestoggle arrow icon

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