Question
Opportunistic fungal infections
Answer
Opportunistic fungal infections occur in individuals with impaired host defences (advanced HIV/AIDS, neutropenia/haematological malignancy, transplant immunosuppression, uncontrolled diabetes, or broad-spectrum antibiotic/corticosteroid use), caused by fungi that are generally of low virulence in immunocompetent hosts.
Important examples:
- Candida species — mucocutaneous (oral/oesophageal thrush) and invasive/systemic candidiasis (candidaemia), particularly in neutropenic or catheterized patients.
- Aspergillus species — invasive pulmonary aspergillosis in severely neutropenic patients, an angioinvasive, often fatal infection.
- Cryptococcus neoformans — cryptococcal meningitis, a classical AIDS-defining infection, acquired by inhalation of yeast from soil contaminated with pigeon droppings.
- Mucorales (Rhizopus, Mucor) — mucormycosis, strongly associated with uncontrolled diabetic ketoacidosis, neutropenia, and (notably) recent COVID-19 with corticosteroid use/hyperglycaemia; markedly angioinvasive.
- Pneumocystis jirovecii — Pneumocystis pneumonia (PCP), a classical AIDS-defining infection.
- Talaromyces (Penicillium) marneffei — disseminated talaromycosis, endemic to Southeast Asia, an AIDS-defining infection there.
Clinical significance: the specific opportunistic fungal infection often correlates with the type of immune defect (cryptococcosis/PCP with defective cell-mediated immunity in AIDS; invasive aspergillosis/mucormycosis with severe neutropenia), guiding clinical suspicion.
Laboratory diagnosis: varies by organism — direct microscopy, culture, antigen detection (cryptococcal antigen, galactomannan for Aspergillus), and histopathology.
Treatment: amphotericin B, azoles (fluconazole, voriconazole, itraconazole), or echinocandins depending on the specific organism and severity, alongside correction of the underlying predisposing immune defect where possible.