Fungal Infections in the Patient With Compromised Defenses

CE U P D A T E M Y C O L O G Y II Peter C. F u c h s, M D, P h D Fungal Infections in the Patient With Compromised Defenses of these infections has increased during the past ABSTRACT Saprobic fungi, traditionally viewed as con- three decades and is in large part an indirect contaminants when recovered from specimens, are increasingly sequence of medical progress. considered to be causes of serious infections, particularly in Factors That Predispose an patients with impaired defenses. This increase is due in Individual to Fungal Infections large part to two facts: These patients are surviving longer, Major factors that predispose an individual to and clinicians are using therapies for these patients that fungal opportunistic infections are listed in the also impair host defenses. The clinical microbiology labora- Table. Patients who are treated with broadtory plays an important role in the diagnosis of these infec- spectrum antibacterial chemotherapy may develop secondary fungal infections. Admintions through study and interpretation of results in the istration of such agents often markedly alters the context of the clinical setting. This is the second article in a continuing education series on mycology. Other articles focus on poisonous mushrooms and indoor air quality. Following this series, readers should be able to identify the eight general types of poisonous mushrooms, identify c o m m o n mycotic opportunists, and understand the investigation and control of fungal contamination in indoor environments. From the Clinical Microbiology Institute, Tualatin, Ore. Reprint requests to Dr Fuchs, the Clinical Microbiology Institute, PO Box 947, Tualatin, OR 97062. Just as bacteria are widespread in nature, so too, are fungi. Fungi are part of the normal human microflora, in which their numbers usually are considerably lower than those of bacteria. Most fungi that colonize the body surfaces (skin, alimentary canal, genital tract, and upper respiratory tract) are yeasts, the most common of which are members of the genus Candida. In their usual numbers, these organisms have a commensal relationship with their hosts (see "A Guide to Terminology)" and thus are of little concern to the healthy individual whose intact skin and mucosae are adequate barriers to infection. In the unhealthy person, however, or in one for whom the normal defensive barriers no longer are intact (eg, a patient with ulcerative lesions of the skin or mucous membranes), these commensal fungi may find conditions conducive to tissue invasion and infection. Such infections are referred to as opportunistic. The prevalence LABORATORY MEDICINE VOLUME 27, NUMBER 6 microbial flora throughout the body by eliminating susceptible bacteria; this permits the overgrowth of resistant microbes, which include any fungi present. Administration of broad-spectrum antibiotics in itself does not increase the risk of infection. If other conditions predisposing a patient to infection are present, however, the likelihood that the etiologic agent will be a fungus is enhanced. An important factor leading to infections is disruption of the integrity of the mechanical barriers presented by normal skin and mucous membranes. Traumatic injuries and third-degree burns are classic examples of skin disruption. Intravenous drug abusers not only sacrifice their skin integrity, but with the common use of unsterile needles and syringes, provide a source of entry for organisms directly into the bloodstream. Medical and surgical procedures also provide unnatural portals of entry for infection. The use of nearly all invasive medical devices is associated with an increased risk of infection, including fungal infection. Such devices include intravascular catheters and devices, urinary catheters, endotracheal tubes, endoscopes, and implanted prostheses. Not only do they provide portals of entry for opportunists, they also act as foreign bodies, which decrease resistance to local infection.

Many diseases are associated with humoral or cellular immunosuppression, or both. In many cases, such as with most malignant tumors, immunosuppression occurs late in the course of the disease. In the past, opportunistic fungal infections were relatively uncommon in patients who had malignant neoplasms, because these patients often died before immunosuppression became a significant factor. Today, patients with advanced disease live much longer owing to better therapies. These patients are more likely to reach a stage of serious immunosuppression, which may be augmented by the immunosuppressive effects of the therapeutic regimen. Many of today's pharmacologic advances have come at the price of increasing susceptibility to opportunistic infections. These drugs include the corticosteroids, which have been in use for 50 years. Many antineoplastic agents destroy rapidly growing and dividing cells, such as cancer cells, but they do not discriminate between cancer cells and normal, rapidly proliferating cells, such as those of the immune system (leading to immunosuppression) or epithelial cells of the alimentary tract (leading to erosive breaches of mucosal barrier). In the current era of organ transplantation, potent drugs designed to suppress the immune system are used to prevent the host from rejecting the implanted foreign organ. C o m m o n M y c o t i c Opportunists The frequency with which some fungi produce opportunistic infections correlates with the prevalence of these agents in the human microflora and immediate environment, particularly at the portals of entry. Candida albicans Candida albicans is the most prevalent of all fungi in the microflora of humans and is also the most common opportunistic fungal pathogen. C albicans can produce a diverse group of infections including dermatoses, thrush, pneumonia, prosthetic valve endocarditis, intravascular line infection, endophthalmitis, and disseminated infection. C albicans grows well not only on mycologic media, but also on most bacteriologic media, including eosin methylene blue agar on which it forms characteristic spider-like colonies (Fig 1). More than 90% produce diagnostic germ tubes in 2 to 3 hours in the germ tube test. Other rapid tests for identification of C albicans, such as Albicans ID (Merioux, Marcy L'Etoile, France), are becoming available commercially. In addition, differential primary culture media such as CHROMagar (CHROMagar, Paris, France) and Fluoroplate (Merck, Damstadt, Germany) agar are reported to yield good recovery and presumptive identification of C albicans. Fig 1. A scanning microscopic view of Candida albicans growing on eosin methylene blue agar at 24 hours. Other Candida Species C tropicalis is the second most common yeast isolated from clinical material. It, along with other species of Candida, commonly is encountered as part of the normal microflora of humans. Although the frequency is less, the spectrum of disease produced by these other species is similar A Guide to Terminology Use this glossary of terms common to the field of mycology to help you in your study of fungal opportunistic infections. Commensal a type of relationship between two organisms that may be beneficial to one, but is not harmful to either. Dermatophycosis fungal infection of the skin. Dimorphic fungi fungi with two distinct morphologic forms; usually a yeast phase at 37 and a mycelial phase at room temperature. Hypha fungal multicelled filamentous structure; cells in a hypha may be separated from each other by septae (septate hyphae) or septae may be rare to absent (nonseptate hyphae). Humoral pertaining to circulating antibodies. Lipophilic fungi fungi requiring fat nutriment for growth. Meninges the membranes that envelop the brain and spinal cord. Microflora the entire population of microorganisms present in or characteristic of a special anatomic site. Opportunistic taking advantage of decreased host defenses. Pathogenicity ability to produce disease. Pseudohyphae hyphal-like structures produced by some yeasts that exhibit constrictions among cells rather than cross septa. Recrudescent reactivated following a dormant or inactive period. Saprobic saprophytic; deriving nourishment from dead or decaying organic material. Zygomycetes fungi that produce zygospores (sexual spores) and sporangiospores (asexual spores). VOLUME 27, NUMBER 6 LABORATORY MEDICINE 385 o 0 u 6

Test Your Knowledge Look for the CE Update exam on Mycology (604) in the July issue of Laboratory Medicine. Participants will earn 3 CMLE credit hours. to that of C albicans. The more common of these Cryptococcus species include C tropicalis, C parapsilosis, C guil- Cryptococcus neoformans is the only true liermondii, C krusei, C lusitaniae, and C kefyr, but pathogen of this genus. It is present in the envimany others have been implicated as well. These ronment, particularly in association with the species usually are identified by assimilation and excretions of pigeons and other birds. It is not part other biochemical tests. Experienced mycologists of the normal human microflora. The infected can identify many species of Candida by micro- person usually has inhaled the organism; it then scopic examination of morphologic features invades the lungs. In healthy individuals, the when they are grown on special media, such as infection usually is contained at this point with cornmeal agar. Depending on the clinical circum- mild or even no symptoms. In immunostances and source of the culture, it may be impor- suppressed individuals, however, the fungus is tant to identify these to species level. Certain more likely to migrate through the bloodstream species have been reported to be associated with to the meninges and central nervous system. This specific clinical settings, and resistance to specific is particularly common in up to 45% of patients antifungal antibiotics is characteristic, or at least with acquired immunodeficiency syndrome common, in some species. For example, C lusita- (AIDS), and is one of the defining infections for niae often is resistant to amphotericin B, and C the clinical diagnosis of AIDS. Severely immunokrusei may be resistant to fluconazole. suppressed individuals may experience true opportunistic infections with "nonpathogenic" cryptococci such as C albidus and C laurentii. Torulopsis glabrata This organism is in taxonomic limbo, because Cryptococci are distinguished readily from most many mycologists believe it belongs in the genus other yeasts by the presence of a capsule (Fig 2). Candida despite its inability to produce pseudo- Rhodotorula also has a capsule, but produces a hyphae. The organism is similar to Candida in its caretenoid pigment. Because nonpathogenic ecology and its potential as an opportunistic cryptococci are common contaminants, it is pathogen. Its prevalence in clinical material is important to distinguish C neoformans from comparable with C tropicalis, although its patho- these. This is done easily by demonstrating the genicity is probably less. production of phenol oxidase, which makes the colonies appear brown on birdseed agar. FACTORS THAT PREDISPOSE A PATIENT TO OPPORTUNISTIC INFECTIONS A. Antibacterial Therapy B. Abnormal Portals of Entry Injury to skin or mucous membranes.surgery Invasive medical procedures and devices Intravenous drug abuse Foreign bodies C. Underlying Disease Associated With Immunosuppression Malignancies Acquired immunodeficiency syndrome (AIDS) Primary immunodeficiency syndromes Diabetes mellitus D. Immunosuppressive Drugs Corticosteroids Anticancer drugs Antirejection drugs for organ transplants LABORATORY MEDICINE VOLUME 27, NUMBER 6 Malassezia The major species of this genus is Malassezia furfur, the etiologic agent of tinea versicolor, a superficial skin mycosis. This obligate lipophilic fungus will not grow on routine fungal culture media unless it is supplemented with long-chain fatty acids. Olive oil typically is used. In light of its lipophilic nature, it is not surprising to see reports of M furfur infections with sepsis involving intravascular lines delivering lipid hyperalimentation. Such infections may be more common than is recognized because most laboratories do not routinely inoculate lipid-rich media. Other Yeasts A variety of other yeasts have been reported to produce infections in immunocompromised patients. Examples include Blastoschizomyces capitis infections, especially in patients with leukemia; Hansenula anomala intravascular line infections; Rhodotorula rubra intravascular line infections with sepsis; peritonitis in ambulatory peritoneal dialysis patients; Saccharomyces cerevisiae fungemia; and systemic infections with Trichosporon beigelii, which may be resistant to amphotericin B.

Aspergillus The genus Aspergillus is the most common mold that produces opportunistic infections. In the compromised host, pulmonary aspergillosis is most common, but disseminated aspergillosis as well as other localized infections involving the sinoorbital region, brain, and so on may occur. Hundreds of species exist within the genus, but the most common opportunist is A fumigatus, followed by A flavus, A niger, and A glaucus. The identity of aspergilli is based primarily on both the macroscopic and microscopic morphology of the organism. For some species, this requires considerable experience. Fortunately, the most important species, A fumigatus, is relatively easy to identify. Most clinical laboratories working with fungi should be able to at least report that an Aspergillus isolate is or is not A fumigatus, because this distinction may have clinical significance. Aspergilli are common laboratory contaminants, and assigning significance to such isolates can be difficult. and Fusarium (keratitis, pulmonary, disseminated). Fig 2. India ink preparation of But many other genera {Paecilomyces, Penicillium, cerebrospinal fluid Acremonium) have been implicated, most often as demonstrating individual case reports. encapsulated Dimorphic Fungi Although dimorphic fungi (eg, Coccidioides immizygomycetes tis, Histoplasma capsulatum) are true pathogens in This group of fungi contains a number of clini- normal hosts, these organisms produce more serically important genera such as Rhizopus, Mucor, ous infections in the immunocompromised host, Rhizomucor, and Absidia. Zygomycetes are molds particularly patients with AIDS. In addition, they normally found in soil and decaying vegetable frequently become reactivated to produce matter. They generally have nonseptate hyphae. recrudescent disease in such patients. To differentiate genera and species within genera, the investigator must use microscopic morpho- Role of the Laboratory logic criteria with specific attention to the spo- Timeliness rangia. The classic zygomycotic infection is Clinicians prefer to obtain instant results. For rhinocerebral mucormycosis, which typically most situations, they have learned to live with the occurs in patients who have uncontrolled dia- inherent slowness of mycologic diagnostic studbetes mellitus. It also may occur in acidosis of ies. The time required to culture samples for other etiologies as well as other immunocompro- acute and systemic fungal infections, however, mised conditions, most notably hematologic often makes the results of historic value only, malignancies. Pulmonary and systemic forms of because patient outcome will already have been zygomycosis also occur in immunocompromised determined by the time the identification is patients, are almost always fatal, and usually are made. Rapid diagnostic tests are appearing diagnosed at autopsy. Timely laboratory diagno- slowly, and these should be used when approprisis of zygomycoses requires direct microscopic ate. The first of these, the latex cryptococcal antiexamination of the specimen (necrotic tissue or gen test, has proven its value during the past two scrapings) and demonstration of the typical decades in the rapid diagnosis of cryptococcal broad-branching nonseptate hyphae (Fig 3). meningitis. Direct microscopic examination of clinical specimens is an old and underused but often valuable rapid test. Depending on the type Other Molds Virtually any of the common "contaminant" sapro- of specimen, direct examinations can be aided bic fungi that can grow at or near body temperature can be potential pathogens under the right conditions. Some of the more common genera implicated in opportunistic infections include Scedosporium (pulmonary, cerebral, disseminated) VOLUME 27, NUMBER 6 budding yeasts typical of Cryptococcus neoformans. LABORATORY MEDICINE! I

depending on the clientele served. Some criteria are fairly universal. For example, yeasts isolated from cerebrospinal fluid should be identified to the fullest extent possible. On the other hand, the extent of identification of yeasts isolated from stool or vaginal specimens will vary considerably among practices. When identifications are made, it is important that they are accurate and consistent. In an immunocompromised patient with suspected disseminated candidiasis, for example, the significance of multiple-site cultures yielding the same species of Candida may be quite different than if each site yielded a different species. Meaningfulness Fig 3. Minced tissue examination (palate) stained with lactophenol cotton blue demonstrating large irregular nonseptate hyphae consistent with Rhizopus species. Meaningfulness of information depends heavily with 20% potassium hydroxide digestion, India on communication between the clinician and ink for demonstrating capsules, or a variety of laboratorian. If no clinical information is providfungal stains, such as calcoflur white. For exam- ed to the laboratory, reported results are generic. ple, the technique is useful in the examination of When appropriate clinical information is providnecrotic tissue from a rhinoorbital lesion in ed to the laboratory, testing can be more specifiwhich zygomycosis is a consideration (see Fig 3). cally directed to the situation and questions at Treatment choice and success depend heavily on hand. For example, an intravascular catheter is early, accurate diagnosis and immediate initiation sent to the laboratory with no clinical informaof appropriate therapy. Waiting for culture results tion and with the request for fungus culture. The (the zygomycetes grow rapidly) usually means microbiologist sets up the routine fungus culture therapy is started too late. Furthermore, in our media. Subsequent preliminary reports and the experience, specimens containing typical final report indicate "no growth." If the clinician zygomycotic hyphae may yield no growth on cul- had notified the laboratory or indicated on the ture. Reducing turnaround time for mycology requisition that this was a hyperalimentation results is becoming increasingly possible and catheter and that he or she was considering M furfur infection, the culture setup would have important. included a lipid-supplemented medium that would support the growth of M furfur. The final Accuracy report, therefore, would have indicated the presalthough inaccurate information can be harmful, ence or absence of M furfur. every fungal isolate does not always need to be identified to species or subspecies level. The extent of identification for usefulness depends on the clinical situation and the source of the specimen. Because the clinical diagnoses seldom are provided routinely to the laboratory, many laboratorians have developed algorithms for extent of identification based on specimen sources. These may vary among laboratories 3 8 8 LABORATORY MEDICINE VOLUME 27, NUMBER 6 Because fungal opportunists are prevalent in the environment and often are components of normal human microflora, their recovery from clinical specimens does not automatically implicate them as infective agents. Many factors must be considered when determining the significance of culture results, and it often requires close communication between the clinician and microbiologist to arrive at a meaningful interpretation. Such communication serves not only the patient. In the era of managed care, the high cost of delays in diagnosis should be strong incentives for health care professionals to communicate better with one another.

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