Clinical relevance for Fungal identification
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p725-726
2025-11-15
59
The question of when and how far to go with the identification of fungi recovered from clinical specimens presents an interesting challenge. The current emphasis on cost containment and the ever-increasing number of opportunistic fungi causing infection in compromised patients prompts consideration of whether all fungi recovered from clinical specimens should be thoroughly identified and reported. A study by Murray et al.8 focused on the time and expense involved in identifying yeasts from respiratory tract specimens. Because these are the specimens most commonly submitted for fungal culture, the researchers questioned whether identifying every organism recovered was important. After evaluating the clinical usefulness of information provided through the identification of yeast recovered from respiratory tract specimens, they suggested the following:
• Routine identification of yeasts recovered in culture from respiratory secretions is not warranted, but all yeasts should be screened for Cryptococcus neoformans complex.
• All respiratory secretions submitted for fungal culture, regardless of the presence or absence of oropharyngeal contamination, should be cultured, because common pathogens, such as H. capsulatum, B. dermatitidis, C. immitis, and S. schenckii, may be recovered.
• Routine identification of yeast in respiratory secretions has little or no value for the clinician and probably represents “normal flora,” except for C. neoformans.
The extent of identification of yeasts from other specimen sources is discussed in Chapter 63. The usefulness of identification and susceptibility testing of non-Cryptococcus yeast isolates was studied by Barenfenger. She found that, compared with only superficial characterization (i.e., “Yeast present, not C. neoformans), identification and susceptibility testing of Candida isolates from respiratory secretions led to unnecessary treatment and increased costs. No statistical difference was seen in the mortality of these groups.
When and how far to proceed in the identification of a mold is a difficult question to answer. Except for obvious plate contaminants, all commonly encountered molds should be identified and reported if recovered from patients at risk for invasive fungal disease. Immunocompromised patients may have serious or even fatal disease caused by fungi that were once thought to be clinically insignificant. Organisms that fail to sporulate after a rea sonable time should be reported as present, but identification is not required if the dimorphic fungi have been ruled out or if the clinician believes the organism is not clinically significant. Ideally, all laboratories should identify all fungi recovered from clinical specimens; however, the limits of practicality and economic considerations play a definite role in the decision-making process. The laboratory director, in consultation with the clinicians being served, must make this decision after considering the patient population, laboratory practice, and eco nomic impact.
As shown in Table 1, an increasing number of fungi may be isolated in the clinical microbiology laboratory. They are considered environmental flora, but in reality must be regarded as potential pathogens because infections with a number of these organisms have been reported. Less commonly encountered fungal pathogens that have been shown to cause human infections include but are not limited to P. boydii; Scedosporium prolificans; Bipolaris, Exserohilum, Trichosporon, and Aureobasidium spp., and others. The laboratory must identify and report all organisms recovered from clinical specimens so that their clinical significance can be determined. In many instances, the presence of environmental fungi is unimportant; however, that is not always the case. Tables 2 and 3 present the molds and yeasts implicated in causing human infection, the time required for their identification, the most likely site for their recovery, and the clinical implications of each.
Table1. Fungi Most Commonly Recovered from Clinical Specimens
Table2. Common Filamentous Fungi Implicated in Human Mycotic Infections
Table2. Common Filamentous Fungi Implicated in Human Mycotic Infections—cont’d
Table3. Common Yeastlike Organisms Implicated in Human Infection*
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