Laboratory Studies
Unfortunately, results from the routine laboratory studies are often nonspecific and not very helpful. Clinicians are required to act definitively and early based on a high index of suspicion. In the past, many patients with life-threatening candidiasis died without receiving antifungal therapy. Systemic candidiasis should be suspected in patients with persistent leukocytosis and either persistent neutropenia or other risk factors and who remain febrile despite broad-spectrum antibiotic therapy. To be effective, antifungal therapy should be provided early and empirically in such high-risk patients. Cultures of nonsterile sites, although not useful for establishing a diagnosis, may demonstrate high degrees of candidal colonization. Always consider positive culture results from sterile sites to be significant and evidence of infection.
In September 2014, the FDA gave marketing approval for the T2Candida Panel and T2Dx Instrument (T2Candida), the first direct blood test for detecting five Candida species that cause bloodstream infections (C albicans and/or C tropicalis, C parapsilosis, C glabrata and/or C krusei). [21, 22] T2Candida can use single blood sample to identify these five yeasts within 3-5 hours, whereas traditional testing methods can take up to 6 days to detect, and even longer to identify, Candida species. Therefore, this test potentially allows earlier administration of appropriate antifungal therapy and may reduce disease severity and/or the mortality risk from sepsis. [21, 22] However, blood cultures should be used to confirm T2Candida results owing to the potential for false-positive results.
Approval was based on a study of 1500 patients, in which T2Candida correctly categorized almost 100% of negative specimens as negative for the presence of Candida, and another study of 300 blood samples with specific concentrations of yeast, in which the test correctly identified the organism in 84%-96% of positive samples. [21, 22]
Mucocutaneous candidiasis
For a wet mount, scrapings or smears obtained from skin, nails, or oral or vaginal mucosa are examined under the microscope for hyphae, pseudohyphae, or budding yeast cells.
A potassium hydroxide smear, Gram stain, or methylene blue is useful for direct demonstration of fungal cells.
Cultures from affected nails may help identify the etiologic agent responsible for onychomycosis versus other noninfectious causes.
Candidemia and disseminated candidiasis [23]
Blood cultures are helpful but yield positive results in only 50%-60% of cases of disseminated infection.
Urinalysis may be helpful and may show either colonization or renal candidiasis.
The serum (1,3)β-D-glucan detection assay (Glucatell, Fungitell) is a nonculture assay that was approved for use in the United States in May 2004. This assay measures the level of β-glucan (a fungal cell wall component). In a large multicenter study, the assay yielded a high specificity and positive predictive value with highly reproducible results. [24]
Cultures of nonsterile sites, although not useful for establishing a diagnosis, may be useful for initiating antifungal therapy in patients with fever that is unresponsive to broad-spectrum antimicrobials. Therefore, appropriate interpretation is required. Positive results from blood cultures and cultures from other sterile sites always imply the presence of invasive disease. Positive results from sterile sites should always be taken as significant and should always prompt treatment.
Gastrointestinal, respiratory, and urinary tract cultures that are positive for Candida may not always represent invasive disease. However, these should be considered sites of colonization.
Cutaneous candidiasis: Using a wet mount, scrapings or smears obtained from skin or nails can be examined under microscopy for hyphae, pseudohyphae, or budding yeast cells. Potassium hydroxide smears are also useful.
Genitourinary candidiasis: A urinalysis should be performed. Evidence of WBCs, RBCs, protein, and yeast cells is common. Additionally, urine fungal cultures are useful.
Respiratory tract candidiasis
Sputum Gram stain may demonstrate WBCs and yeast cells.
Sputum cultures may demonstrate Candida species.
Lung biopsy is mandatory to definitively establish the diagnosis of respiratory tract candidiasis because of the high frequency of yeast colonization of the respiratory tract.
Gastrointestinal candidiasis
Endoscopy with or without biopsy is necessary to establish the diagnosis.
Focal hepatosplenic candidiasis
Serum alkaline phosphatase levels are commonly elevated.
Species identification
C albicans, C dubliniensis, and Candida stellatoidea can be identified morphologically via germ-tube formation (hyphae are produced from yeast cells after 2-3 h of incubation) or biochemical assays.
CHROMagar Candida allows for the presumptive identification of several Candida species by using color reactions in specialized media that demonstrate different colony colors depending on the species of Candida.
API20C and API32C are biochemical assays that allow for the identification of the different Candida species with more precision. These assays evaluate the assimilation of numerous carbon substrates and generate profiles used in the identification of different fungal species.
The C albicans peptide nucleic acid (PNA) fluorescence in situ hybridization (FISH) test can be used to identify C albicans in 24-48 hours when the probe is added to smears that are made directly from the blood culture bottle and followed by hybridization. A newer version of this test now allows for the simultaneous identification of either C albicans or C glabrata. [25]
Antifungal susceptibility testing
In vitro susceptibility testing for Candida species is now standardized using the Clinical Laboratory Standards Institute (CLSI) microbroth dilution (CLSI M27-A2, 2002) or the disk diffusion (CLSI M44-P, 2003) methodology. This was formerly known as the National Committee for Clinical Laboratory Standards (NCCLS) microbroth dilution.
These methods may be helpful in guiding difficult therapeutic decisions. Most of the difficult decisions involve antifungal-refractory oral or esophageal candidiasis in patients with advanced HIV disease.
Nonculture Candida detection assays
The Candida mannan assay yields a sensitivity of 31%-90% (less for non-albicans Candida species).
The Candida heat labile antigen assay yields a sensitivity of 10%-71%.
The D-arabinitol assay yields a sensitivity of 50% but is not useful for infection with C krusei or C glabrata.
The enolase assay yields a sensitivity of 55%-75%, which improves with serial testing.
The (1,3)β-D-glucan assay is an amebocyte lysis assay with a sensitivity of 75-100% and a specificity of 88%-100%. It is a broad-spectrum assay that detects Aspergillus, Candida, Fusarium, Acremonium, and Saccharomyces species. β-D-glucan is a cell wall component in a wide variety of fungi and can be detected based on its ability to activate factor G of the horseshoe crab coagulation cascade. The Fungitell assay may be used in the evaluation of invasive fungal infections caused by the fungi mentioned above. The assay does not detect infections caused by Cryptococcus neoformans or Zygomycetes.
Molecular assays such as the polymerase chain reaction (PCR) assay and DNA probes are still under development and in the early investigational phases, but they appear promising.
A new, rapid test for Candida infections of the bloodstream may cut patient mortality from 40% to 11% by diagnosing candidemia 25 times faster than blood culture can and quickly identifying the Candida species that is causing the infection. The new test, T2Candida, uses polymerase chain reaction (PCR) assay to amplify Candida DNA in blood, with the genetic material hybridizing to superparamagnetic nanoparticles coated with complementary DNA. The nanoparticles aggregate into "microclusters," which greatly alter a T2 magnetic resonance (T2MR) signal. [26, 27]
Imaging Studies
Imaging studies are not required or useful in the diagnosis of cutaneous candidiasis, oropharyngeal candidiasis (OPC), or vulvovaginal candidiasis (VVC).
Chest radiography may be useful in differentiating a bacterial pneumonia as the cause of fever in patients who are hospitalized. Patients with bronchopneumonia due to hematogenous candidiasis usually have multilobar involvement.
Esophagography/upper gastrointestinal studies may be useful for detecting abnormalities in the esophagus and stomach. Unfortunately, these studies are not helpful in determining the microbiologic etiology of the infection.
Ultrasonography may be useful for diagnosing hepatosplenic abscess. The classic bull's eye or target lesions are observed in the liver and spleen.
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Echogenic foci with degrees of shadowing
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Intra-abdominal abscess formation
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Cholelithiasis
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Renal abscess
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Renal fungus balls
CT scanning with contrast enhancement may be useful for diagnosing the following:
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Hepatosplenic candidiasis
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Intra-abdominal abscess or peritonitis
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Renal abscess
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Pyelonephritis
Echocardiography may be useful for excluding or including Candida endocarditis as a possible diagnosis. It is extremely useful because fungal endocarditis is frequently associated with large vegetations that are easily observed on standard echocardiograms.
Procedures
In patients with candidemia or disseminated candidiasis, obtaining a tissue biopsy of the involved areas is frequently helpful in establishing the presence of Candida infection and invasion.
Bronchoscopy with bronchoalveolar lavage and transbronchial biopsy provide adequate tissue for diagnosis of pulmonary candidiasis.
Endoscopy provides direct examination of the esophagus and stomach, one of the organ systems most commonly infected with Candida species. It is also necessary for excluding other causes of esophagitis.
Echocardiography may be useful for excluding or including Candida species as a cause of endocarditis. It is extremely useful because fungal endocarditis is frequently associated with large vegetations that are easily observed using standard echocardiography.
Histologic Findings
Fixed tissues can be stained with hematoxylin and eosin. In addition, fungal hyphae may be demonstrated with Grocott silver-methenamine, methylene blue, or periodic acid-Schiff staining. The classic appearance demonstrates the Candida species as either round or ovoid yeast cells, hyphae, or pseudohyphae.
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A moist, erosive, pruritic patch of perianal skin and perineum (with satellite pustule formation) is demonstrated in this woman with extensive candidiasis. Courtesy of Matthew C. Lambiase, DO.
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Discrete superficial pustules developed within hours of birth on the hand of an otherwise healthy newborn. A potassium hydroxide preparation revealed spores and pseudomycelium, and culture demonstrated the presence of Candida albicans. Courtesy of Matthew C. Lambiase, DO.
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Dry, red, superficially scaly, pruritic macules and patches on the penis represent candidal balanitis. Courtesy of Matthew C. Lambiase, DO.
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White plaques are present on the buccal mucosa and the undersurface of the tongue and represent thrush. When wiped off, the plaques leave red erosive areas. Courtesy of Matthew C. Lambiase, DO.
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Erythema, maceration, and satellite pustules in the axilla, accompanied by soreness and pruritus, result in a form of intertrigo. Courtesy of Matthew C. Lambiase, DO.
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A nailfold with candidal infection becomes erythematous, swollen, and tender with occasional discharge. Courtesy of Matthew C. Lambiase, DO.
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Soreness and cracks at the lateral angles of the mouth (angular cheilitis) are a frequent expression of candidiasis in elderly individuals. Courtesy of Matthew C. Lambiase, DO.
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Fine, superficial pustules on an erythematous patchy base are suggestive of candidiasis. Courtesy of Matthew C. Lambiase, DO.
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Candidal infection should be in the differential diagnosis when one or more nails become discolored, have subungual discoloration, have nailplate separation from the nailbed, and lack evidence of a dermatophyte. Courtesy of Matthew C. Lambiase, DO.
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Candida dermatitis in the diaper area. Courtesy of Hon Pak, MD.
