Opportunistic Mycoses - Microbiology

Snapshot

A 40-year-old woman presents to the emergency room with a week of fever, cough, and hemoptysis. She has a history of HIV and has been noncompliant with her medications and has a history of tuberculosis that was adequately treated. She reports feeling increasing fatigue. A chest CT shows nodules with a halo sign. A bronchoalveolar lavage with biopsy eventually reveals fungus with septate hyphae branching at acute angles invading into lung tissue. (Invasive aspergillosis)

Candida albicans

Classification
- yeast with budding and pseudohyphae
- germ tube formation at 37°C (diagnostic)
- can be part of normal flora
Risk factors
- immunocompromised status
- hospital admission, especially in the ICU
Clinical syndrome
- immunocompetent hosts present with skin and mucous membrane infections
  - oral thrush
    - white plaque on the tongue that can be scraped off
    - associated with use of inhaled corticosteroids
  - candidal intertrigo
    - well-demarcated, erythematous, and itchy plaques in the skin folds
  - vulvovaginitis
    - thick "cottage cheese" white discharge
    - itchiness
- immunocompromised hosts usually present with systemic disease
  - local infection is due to T-cell deficiency while systemic infection is due to neutropenia
  - esophagitis
    - dysphagia and throat pain
    - endoscopy shows white plaques along the esophagus
  - endocarditis
    - associated with IV drug users
    - fevers and a new murmur
  - disseminated/invasive candidiasis
    - fever and septic shock
Studies
- definitive diagnosis requires blood or other tissue culture
- wet mount with potassium hydroxide prep of vaginal fluid shows yeast with pseudohyphae
- germ tube formation at 37°C
Treatment
- nystatin
  - local infections
- azoles
  - local and systemic infections
  - first-line if the fungus is not resistant
- echinocandins
  - systemic infections
  - first-line due to increased resistance to azoles
- amphotericin B
  - systemic infections
  - second-line or for pregnant women

Cryptococcus neoformans

Classification
- urease-positive monomorphic encapsulated yeast with 5-10 μm narrow budding
- transmitted via inhalation and found in soil and pigeon droppings
Risk factors
- immunocompromised status
- HIV/AIDS patients
Clinical syndrome
- pulmonary cryptococcosis
  - most common site of infection
- cryptococcal meningitis
- cryptococcal encephalitis
- presents with fevers, headaches, and generalized malaise
Studies and imaging
- head imaging with computed tomography (CT) or magnetic resonance imaging (MRI)
  - soap bubble lesions
  - variable enhancing lesions
  - hydrocephalus
- detection of capsular antigen in serum or cerebrospinal fluid (CSF)
  - latex agglutination test
- CSF studies
  - culture on Sabouraud agar
  - India ink stain shows yeast with clear halos
  - mucicarmine shows yeast with red inner capsules
Treatment
- amphotericin B + flucytosine
  - for 10-14 days
- fluconazole
  - after treatment with amphotericin B and flucytosine
  - maintenance and suppressive therapy

Aspergillus spp.

Classification
- most commonly Aspergillus fumigatus
- monomorphic fungus with septate hyphae branching at acute angles (45 degrees)
- found in soil and decomposed material
- transmission via inhalation of spores called conidia
Risk factors
- immunocompromised status
- hematologic malignancy
- asthma
- pre-existing lung disease
Clinical syndrome
- invasive aspergillosis
  - invasive infection of the lung
  - causes persistent fever and cough with hemoptysis
- aspergilloma
  - mycetoma ("fungal ball") in pre-existing cavity (i.e., tuberculosis)
  - causes cough with hemoptysis or asymptomatic
- allergic bronchopulmonary aspergillosis (ABPA)
  - hypersensitivity reaction in patients with cystic fibrosis or asthma
  - causes bronchiectasis and eosinophilia
  - causes cough with hemoptysis, brownish black mucus plugs in expectorate, and wheezing
Studies and imaging
- invasive aspergillosis
  - nodules with halo sign and cavitary lesions on computed tomography (CT)
  - pathologic examination showing invasive hyphae into tissue
  - positive cultures or serology
- aspergilloma
  - mobile round or ovoid mass on chest CT
  - positive cultures or serology
- ABPA
  - bronchiectasis on CT
  - elevated eosinophils or IgE in ABPA
Treatment
- invasive aspergilloma
  - voriconazole + amphotericin B
    - first-line
  - caspofungin
    - second-line
- aspergilloma
  - surgical resection
- ABPA
  - steroids
    - first-line

Mucormycosis

Classification
- Mucor and Rhizopus spp.
  - fungi with irregular, broad, and nonseptate hyphae branching at wide or right angles
  - found in soil and decomposed material
  - transmission via inhalation of spores or direct inoculation through trauma
Risk factors
- diabetic ketoacidosis
- immunocompromised status
- trauma or burns
Clinical syndrome
- mucormycosis (rhinocerebral infection)
  - headache
  - congestion
  - sinus pressure and pain
  - black necrotic eschar on face, particular nares or palate
Studies and imaging
- computed tomography (CT) shows air-fluid levels in the sinuses and bony destruction
- biopsy of affected tissue shows nonseptate hyphae with wide-angle branching
Treatment
- amphotericin B
  - first-line
- isavuconazole
  - second-line
- surgical debridement
  - for patients who need it, in addition to antifungals

Pneumocystis jiroveci

Classification
- a yeast-like fungus
- transmission via airborne
Risk factors
- immunocompromised status (e.g., hyper IgM syndrome)
- HIV
- smoking
Clinical syndrome
- interstitial pneumonia
  - progressive exertional dyspnea
  - chest pain
  - nonproductive cough
  - fever and chills
  - hemoptysis is rare
Imaging
- chest radiograph will show bilateral infiltrates
- computed tomography will show patchy ground-glass opacities sand pneumatoceles
Studies
- histology with methenamine silver, Diff-Quik, or Wright stain of lung tissue
  - disc-shaped yeast
Treatment
- trimethoprim-sulfamethoxazole (TMP-SMX)
  - prophylaxis (CD4+ count < 200 cells/mm³) and first-line therapy
- corticosteroids
  - severe cases
- pentamidine, atovaquone, or dapsone
  - second-line therapy if resistant to TMP-SMX or allergic