Mycology Test List

[Nico Sadiq]

WHO is developing a model list of \"essential bacteriology and mycology diagnostic tests\". This list aims to complement the WHO Essential Diagnostic List (EDL) and to assist countries on the rational placement of bacteriology and mycology diagnostic tests at the different levels of the health care system, from primary care to tertiary-level hospitals, with a particular focus in low- resource settings.

WHO has designed an online survey to gather inputs from microbiologists, infectious diseases clinicians, and laboratory health systems experts. The opinions, values and preferences of these stakeholders are sought on the clinical utility of the tests, their importance for antimicrobial resistance mitigation, technical complexity in performing the tests, and their affordability. A parallel survey addressed to Ministries of Health in all WHO member states is currently ongoing.

WHO is developing a model list of "essential bacteriology and mycology diagnostic tests". This list aims to complement the WHO Essential Diagnostic List (EDL) and to assist countries on the rational placement of bacteriology and mycology diagnostic tests at the different levels of the health care system, from primary care to tertiary-level hospitals, with a particular focus in low- resource settings.

Culture for fungi. Isolation and identification (additional charges/CPT code[s] may apply) if culture results warrant. CPT coding for microbiology and virology procedures often cannot be determined before the culture is performed.

Avoid contamination of the specimen with commensal organisms as much as possible. Specify the source of the specimen and include any pertinent clinical information. Cultures are incubated one to four weeks (depending on source) before a final negative report is issued.

Unlabeled specimen or name discrepancy between specimen and request label; specimen received after prolonged transport (usually more than 72 hours); lithium heparin tube; swab without evidence of specimen present; specimen received after leaking transport container into specimen bag; inappropriate transport device, including syringe with needle. (Trach-suction devices will often leak if the cap with tubing is not removed and replaced by a solid cap. This may need to be done by personnel collecting the specimen as the solid cap is usually in with the device. If there is not solid cap, the specimen should be transferred to a leakproof sterile cup with metal cap.)

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.

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 38.5C (101F) 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

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.

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

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