Fungus (Mycology) Culture

Biopsy, blood, body fluid, aspirates, bronchoalveolar lavage (BAL), swab of conjunctiva, skin, nails, hair, sputum, stool, throat, tissue, urine, or vaginal

2 mL or 1 cm³ tissue, 10 mL blood, whole nails, 50 mL body fluid (5 mL CSF), 5 mL aspirates or sputum; skin scrapings may be submitted on Mycosel® medium (not supplied by LabCorp)

Sterile container for fluid or tissue or green-top (sodium heparin) tube, blood culture bottle, Para-Pak White for stool

Usual sterile preparation (see Blood Culture, Routine [008300]).

Isolate and identify fungi. Blood: establish the diagnosis of fungal infections including fungemia, fungal endocarditis, and disseminated mycosis in patients at risk for fungal infections.

Blood: A single (or even multiple) negative fungal blood culture does not exclude disseminated fungal infection. If disseminated or deep fungal infection is strongly suspected despite repeatedly negative blood cultures, biopsy of the appropriate tissue and/or bone marrow aspiration for sections and fungus culture should be considered.

Stool: Use of this test is generally limited to detection of Candida. Stool cultures have a low yield and are not recommended for the isolation of systemic fungi; however, Histoplasma capsulatum is recovered from the stool of AIDS patients with disseminated infection.

Culture

Blood: Fungemia can be a complication of venous or arterial catheterization, hyperalimentation, the acquired immunodeficiency syndrome (AIDS), and therapy with steroids, antineoplastic drugs, radiation, or broad spectrum antimicrobial agents. Intravenous drug abusers are prone to Candida endocarditis. Although many fungal species, including Histoplasma capsulatum, Coccidioides immitis, and Cryptococcus neoformans are recoverable from blood cultures, the most common cause of fungemia is Candida albicans followed by other Candida sp, including Candida glabrata. Fungemia represents a failure of the host defense system. Fungemia may be precipitated by contamination of an indwelling catheter or, in the critically ill and immunocompromised patient, contamination of the gastrointestinal and less frequently the urinary tract.¹ In a review of 356 patients with neoplastic disease, Candida sp was recovered in 7% of neutropenic patients.

In the potentially immunocompromised host, a temperature of 38.5°C (101°F) for more than two hours, which is not associated with the administration of a pyrogenic drug (chemotherapy), indicates the presence of infection until proven otherwise. In these patients, characteristic signs and symptoms are frequently absent. A careful physical examination, including mouth, anus, and genitalia, may reveal the site of infection. Therapy must be instituted as soon as appropriate specimens are collected. Most infections in these patients are caused by gram-negative organisms (eg, E coli, Pseudomonas sp, Klebsiella sp) and by S aureus; however, fungi and other usually nonpathogenic organisms must be considered significant.²

Rarely, blastospores (budding yeast structures) and pseudohyphae can be seen by examination of Wright-stained venous peripheral blood smears. This technique may allow early diagnosis and therapy before culture results are available.³

Eye: The more common causes of keratomycosis include Fusarium solani, Candida albicans, Aspergillus fumigatus, Curvularia sp, Aspergillus flavus, other species of Aspergillus, Penicillium, Paecilomyces, Fusarium, and many other species.⁴ A keratomycosis-like clinical presentation may also be encountered caused by Nocardia asteroides and Mycobacterium fortuitum. Keratomycosis is a rare complication of contact lens use.⁵

Sinus: Fungal sinusitis has been increasingly recognized in otherwise healthy teenagers who often present with a history of recurrent sinusitis, asthma, and/or polyps. At surgery, material is consistently described as thick peanut butter-like or pistachio pudding-like. Dematiaceous fungi are the most common cause.

Skin: Candida sp may colonize skin. Clinical diagnosis of Candida infection involves consideration of predisposing factors such as occlusion, maceration altered cutaneous barrier function. Signs of Candida infection include bright erythema, fragile papulopustules, and satellite lesions.⁶ Patients with defects in T-lymphocyte responses, such as AIDS patients or individuals being treated with antineoplastic drugs, are especially susceptible to many fungal infections including superficial mycoses.^7,8 See tables.

Hair: The leading agent of tinea capitis in the United States is Trichophyton tonsurans. Other dermatophytes such as T violaceum, T mentagrophytes, and Microsporum canis are also recovered routinely. Unlike at the beginning of the 20th century, M audouinii is rarely seen.

Nails: Nail disease can be caused by dermatophytes and nondermatophytes. The leading cause of nail infection is Trichophyton rubrum, but it is not unusual to find T mentagrophytes and T tonsurans. Recovery of dermatophytes from nail can be difficult and careful cleansing, scraping of the diseased nail, and collecting debris under the nail is required. Attributing nail disease to nondermatophytes is more problematic. Fungi such as Fusarium, Scopulariopsis, and some aspergilli are routinely associated with disease, however, Chrysosporium, Paecilomyces, Trichoderma and others may likely represent environmental contamination unless repeatedly isolated in the absence of other pathogens.

Sputum: Deeply coughed sputum, transtracheal aspirate, bronchial washing or brushing, or deep tracheal aspirate are preferred specimens. Oncology patients, transplant patients, and patients with the acquired immunodeficiency syndrome (AIDS) are particularly prone to infection with fungi.⁸

Primary fungal pulmonary infections include Histoplasma capsulatum, Coccidioides immitis, Cryptococcus neoformans, and Blastomyces dermatitidis. The incidence is largely related to geographic exposure and cases can occur in seemingly normal hosts. Numbers of reports of opportunistic fungal pulmonary infections due to a variety of etiologic agents that are ubiquitous in the environment are being published. Definitive diagnosis depends upon the presence of clinical signs of pulmonary infection, a chest x-ray revealing abnormality such as granuloma; laboratory isolation of a potentially significant organism from a suitable specimen; histologic documentation of tissue invasion by the isolated organism. A list of etiologic agents of pulmonary fungal disease has been compiled.⁹ In practice a diagnosis sufficient for therapy can frequently be established by observation of hyphae, pseudohyphae, spherules, or yeast cells in tissue sections; recovery of the organism from a normally sterile site; repeated isolation of the same suspect organism from the same or different sites; seroconversion (ie, the development of an immune response to the suspected organism).¹⁰ Candida and Aspergillus sp are the most frequently isolated fungal organisms; however, they are frequently present as the result of contamination from the patient's normal flora or airborne sources. Their presence may represent colonization rather than invasion. Recovery of Candida from blood is a major adjunct to definitive diagnosis. Even without invasion Aspergillus may cause IgE mediated asthma, allergic alveolitis cell mediated hypersensitivity, mucoid impaction, and bronchocentric granulomatosis.¹¹ Fungal tracheobronchitis has recently been recognized as a pseudomembranous form involving the circumference of the bronchial wall or as multiple or discrete plaques. The plaques or pseudomembranes are composed of necrotic tissue exudate and fungal hyphae.¹²

Stool: Candida can be isolated in up to 30% of oropharyngeal cultures and 65% of stool cultures; thus, it is a common saprophyte.¹³ Neonates and adults may develop watery diarrhea due to intestinal overgrowth by yeast that readily responds to specific therapy. Candida may become disseminated in patients with leukopenia, immunosuppressive therapy, AIDS, corticosteroid therapy, phagocytic defects, hyperalimentation, use of broad spectrum antibiotics, and oral contraceptives. Travelers in endemic areas with poor sanitation have also experienced intestinal overgrowth with Candida, although the specific mechanism causing diarrhea is unknown.¹⁴

Candida-associated diarrhea is predominantly of the secretory type, characterized by frequent watery stools, usually without blood, mucus, tenesmus, or abdominal pain.¹⁵ Overgrowth of Candida sp should be considered when evaluating Clostridium difficile negative cases of antibiotic-associated colitis.¹⁶

Urine: Asymptomatic funguria often clears spontaneously; however, candiduria with >15,000 colony forming units/mL of urine and with such evidence of dissemination as elevated serum precipitin antibody titers, is associated with increased mortality.¹⁷ Patients with candiduria may or may not have candidemia; positive urine culture for fungi often may be followed by positive blood culture for fungi. Ascending infections occur in patients with diabetes, prolonged antimicrobial therapy, or following instrumentation. Urinary obstruction due to “fungus balls” may occur in diabetes and following renal transplantation. Candiduria associated with hematogenous infections is observed in patients with granulocytopenia, corticosteroid therapy, and with immunosuppression. The source is frequently the gastrointestinal tract or indwelling catheters particular with hyperalimentation.¹⁸ A blood fungus culture is useful to define invasive disease; however, proof of invasive Candida infection requires direct cystoscopic or operative visualization, fungus balls, pyelonephritis, or histological evidence of mucosa invasion. Urine is a useful specimen for culture in cryptococcosis, blastomycosis, and candidiasis. The incidence of genitourinary fungal infections is increasing. They are usually associated with broad spectrum antibiotic therapy, corticosteroid therapy, underlying general debility, and AIDS. In addition to Candida, opportunistic pathogens in the genitourinary tract include Aspergillus and Cryptococcus. Endemic pathogens such as Histoplasma, Blastomyces, and Coccidioides are also encountered.¹⁹

Mold spores are common in the environment and it is not uncommon for saprophytic environmental fungi to be recovered from respiratory and skin specimens.