Fungal diseases, also known as mycoses, are common in healthcare settings. According to the CDC, Candida is one of the most common causes of healthcare-associated bloodstream infections. Like some antibiotic medications, some antifungal medications are becoming resistant to first- and second-line medications (fluconazole and echinocandins). Some studies indicate that use of antibiotic medications contributes to antifungal resistance (Table 7.5). Fungi prefer the debilitated host, the person with chronic disease or impaired immunity, or a patient who has been receiving prolonged antibiotic therapy.
Of more than 200,000 species of fungi, approximately 200 species are generally recognized as being pathogenic for humans. Fungi live in soil enriched by decaying nitrogenous matter and are capable of maintaining a separate existence through a parasitic cycle in humans or animals. The systemic mycoses are not communicable in the usual sense of human-to-human or animal-to-animal transfer. Humans become accidental hosts through inhalation of spores or by introduction of spores into tissues through trauma. Altered susceptibility may result in fungal lesions; this frequently occurs in patients who have a debilitating disease, diabetes, or impaired immunologic responses due to steroid or antimetabolite therapy. Prolonged administration of antibiotic medications can result in a fungal superinfection.
Fungal diseases may be classified according to the type of tissues involved:
Dermatophytoses include superficial and cutaneous mycoses, such as athlete’s foot, ringworm, and jock itch. Species of Microsporum, Epidermophyton, and Trichophyton are the causative organisms.
Subcutaneous mycoses involve the subcutaneous tissues and muscles.
Systemic mycoses involve the deep tissues and organs and are the most serious of the three groups.
Amphotericin B, introduced into practice in 1958, was for many years the only drug available to treat invasive fungal infections. Now ketoconazole, fluconazole, itraconazole, and lipid formulations of amphotericin B provide alternative choices when treatment of fungal disease is warranted.
Clean the suspected area with 70% alcohol to remove bacteria. Use sterile techniques and standard precautions.
Scrape the peripheral erythematous margin of putative ringworm lesions with a sterile scalpel or wooden spatula and place the scrapings in a covered sterile container.
Clip samples of infected scalp or beard hair and place in a covered sterile container.
Pluck hair stubs out with tweezers because the fungus is usually found at the base of the hair shaft. Use of a Wood light in a darkened room helps identify the infected hairs.
Samples from infected nails should be procured from beneath the nail plate to obtain softened material from the nail bed. If this is not possible, collect shavings from the deeper portions of the nail and place them in a covered sterile container.
A Wood light is used to determine presence of a fungus directly on hair. A Wood light is a lamp that uses ultraviolet rays of 3660 A. In a darkened room, infected hairs fluoresce a bright yellow-green under the Wood light.
Direct microscopic examination of tissue samples placed on a slide is performed to determine whether a fungus is actually present. The potassium hydroxide (KOH) test or Calcofluor white stain test is used to detect the presence of mycelial fragments, arthrospores, spherules, or budding yeast cells and involves mixing the specimen with the reagent on a glass slide. The slide is then microscopically examined for fungal elements.
A fluorescent stain, Calcofluor white, fluoresces when exposed to ultraviolet light. This reagent stains the fungi, causing them to exhibit a fluorescence that can be detected microscopically. It can be used on tissue and has the same sensitivity as KOH. Moreover, it allows for easier and faster detection of fungal elements. Calcofluor white–stained specimens can also be examined under bright-field or phase-contrast microscopy.
Cultures are done to identify the specific type of fungus. Fungi are slow growing and are subject to overgrowth by contaminating and more rapidly growing organisms. Fungemia (fungus in the blood) is an opportunistic infection, and often, a blood culture reveals the earliest suggestion of the causative organism.
For fungal serology tests, single titers greater than 1:32 usually indicate the presence of disease. A fourfold or greater rise in titer of samples drawn 3 weeks apart is significant. However, serologic diagnosis of Candida and Aspergillus species can be disappointing. Complement fixation tests for histoplasmosis and coccidioidomycosis can aid in the diagnosis of these diseases. The immunodiffusion test is helpful for the diagnosis of blastomycosis.
Antigen tests performed on urine specimens are available for the detection of disseminated Histoplasma capsulatum and Blastomyces dermatitidis. The urinary antigen test has a 92% sensitivity.
Skin
Nails
Hair
Ulcer scrapings
Pus
CSF
Urine
Blood
Bone marrow
Stool
Bronchial washings
Tissue biopsy specimens
Prostatic secretions
Sputum