Candidiasis

Definition

Candidiasis encompasses a wide variety of clinical syndromes caused by yeasts of the genus Candida . Of the species that cause infection in humans, Candida albicans is the most common; Candida glabrata, Candida parapsilosis , and Candida tropicalis are responsible for most of the remaining infections, but Candida auris has emerged as a major pathogen in some parts of the world. Organisms such as Candida krusei, Candida lusitaniae , and Candida guilliermondii are less common causes of infection.

Epidemiology

C. albicans is the species most commonly found colonizing humans; C. glabrata is the second most common species, and C. tropicalis, C. parapsilosis , and others are found less often. C. glabrata , a species that is increasingly resistant to fluconazole, has become a prominent pathogen in many hospitals. In many parts of the world, C. auris , a previously uncommon multidrug-resistant Candida species, has caused outbreaks and created new challenges in understanding the epidemiology, treatment, and prevention of this organism.

Though uncommon, acquisition of Candida from environmental sources has been noted. The Candida species most often associated with transmission from contaminated fluids or devices, especially central intravenous catheters, is C. parapsilosis .

Candidiasis is the most common opportunistic fungal infection as a result of both the organisms’ ubiquity and the increasing number of patients who have risk factors for infection with these organisms. The classic immunosuppressed host at risk for serious Candida infections is a neutropenic patient who has a hematologic malignancy and who has received cytotoxic agents and corticosteroids. Candidiasis is increasingly being seen in patients who are in intensive care units (ICUs). Risk factors for the development of serious Candida infections in ICU patients include diabetes, the use of broad-spectrum antimicrobial agents, indwelling central venous catheters, intravenous drug use ( Chapter 365 ), previous surgical procedures, renal failure, parenteral nutrition, pancreatitis, dialysis, and a high Acute Physiology and Chronic Health Evaluation (APACHE) score. Certain ICU populations, especially burn victims ( Chapter 97 ), are at even higher risk for Candida infection than is the typical ICU patient.

The primary manifestation of Candida infection in patients with HIV/AIDS ( Chapter 358 ) is mucocutaneous infection, primarily oropharyngeal candidiasis. The development of mucosal Candida infection is related to deficient T-cell immunity as reflected by a low CD4 lymphocyte count. With current antiretroviral therapy, oropharyngeal and esophageal candidiasis are much less common.

Pathobiology

The usual mode of infection with Candida is egress from its normal niche into the bloodstream or other tissues; the source is usually the gastrointestinal tract, but the skin and genitourinary tract are other sources. The primary host defense in response to this event is phagocytosis and killing by neutrophils, monocytes, and macrophages. C-C chemokine receptor 2 (CCR2)-expressing inflammatory monocytes and their tissue-resident derivatives play an essential antifungal role, particularly in the first 48 hours after Candida infection. Phagocytosis is enhanced in the presence of specific anti- Candida antibody and complement. Several different mechanisms are operative within neutrophils and macrophages that allow the killing of yeasts. Thus, patients who are leukopenic ( Chapter 153 ), especially those with chemotherapy-induced disruption of the gut mucosa, are at great risk for invasion with Candida species. Once Candida gains access to the bloodstream, widespread hematogenous dissemination is the rule. Biopsy of involved organs shows multiple microabscesses composed of neutrophils (in a host who has these cells), budding yeasts, and often pseudohyphae or hyphae. Over time, the lesions show a mixed neutrophilic and granulomatous response.

T-cell immunity is an important host defense against infection with Candida at mucosal surfaces. In contrast to patients with neutropenia, patients with deficient T-cell immunity are at risk for persistent and recurrent mucocutaneous candidiasis, but invasive infection rarely develops.

Clinical Manifestations

Mucocutaneous Candidiasis

Oropharyngeal Candidiasis

Local mucous membrane and cutaneous lesions are the most common forms of Candida infection. Oropharyngeal candidiasis, or thrush ( Chapter 393 ), can be due to either local factors or T-cell dysfunction. Local factors include the use of broad-spectrum antimicrobial agents, inhaled corticosteroids, xerostomia ( Chapter 393 ), and radiation treatment of the head and neck. Denture stomatitis occurs frequently in persons who wear full upper dentures, especially individuals who do not remove their dentures at night.

Thrush secondary to T-cell dysfunction is most commonly seen in patients with HIV infection ( Chapter 358 ) and is the most frequent opportunistic infection noted in patients with AIDS. The appearance of thrush in a previously healthy individual with no known risk factors should immediately raise suspicion of HIV infection.

Thrush manifests with white plaques on the buccal mucosa, palate, oropharynx, or tongue ( Fig. 310-1 ). Scraping the lesions with a tongue depressor reveals an erythematous, nonulcerated mucosa under the plaques. Denture stomatitis almost always manifests as a painful erythematous palate without plaques. Angular cheilitis, or perlàche, which is the presence of painful cracks at the corners of the mouth, can occur with or without thrush.

Esophagitis

Esophagitis may accompany oropharyngeal candidiasis or may occur independently of lesions in the oropharynx ( Chapter 124 ). The development of Candida esophagitis is almost always related to immune dysfunction and not simply to local factors. Candida esophagitis occurs in patients with AIDS and low CD4 counts, patients with leukemia, and patients who are taking immunosuppressive agents. Candida esophagitis occurs rarely in otherwise normal hosts. The classic symptom of Candida esophagitis is odynophagia localized to a discrete substernal area. The differential diagnosis includes ulcerations due to herpes simplex or cytomegalovirus and, in patients with AIDS, idiopathic ulcers.

Vulvovaginitis

Candida vulvovaginitis is a common infection in women of childbearing age and is the most frequent mucocutaneous manifestation of Candida infection. Risk factors include conditions associated with increased estrogen levels, such as the use of oral contraceptives and pregnancy, diabetes mellitus, therapy with corticosteroids or broad-spectrum antimicrobials, and HIV infection. Symptoms include vaginal discomfort, discharge, and vulvar pruritus. The discharge is usually curdlike, but it can also be thin and watery. The labia are erythematous and swollen, and the vaginal walls show erythema and white plaques. Although most women have only a few episodes throughout their lives, a minority have frequent recurrences; in most of these patients, no discrete risk factor can be identified, and the cause is presumed to be local immune dysregulation.

Cutaneous Candidiasis

Candida infection of the skin ( Chapter 405 ) occurs mostly in the intertriginous areas or under a large pannus or pendulous breasts. The lesions, which are erythematous, pruritic, and frequently pustular, have a distinct border and are almost always associated with smaller satellite lesions, which help distinguish candidiasis from tinea cruris or corporis. Candida onychomycosis results in thickened, opaque, and onycholytic nails ( Chapter 409 ). Candida can also cause paronychia, especially in patients whose occupation involves frequent immersion of the hands in water.

Chronic Mucocutaneous Candidiasis

Chronic mucocutaneous candidiasis is an uncommon syndrome that usually begins in childhood and is characterized by recalcitrant and relapsing thrush, esophagitis, vaginitis, onychomycosis, and hyperkeratotic skin lesions on the face, scalp, and hands. Autosomal dominant chronic mucocutaneous candidiasis is associated with mutations in the CC domain of STAT1 , thereby leading to defective T _H 1 and T _H 17 responses. Some patients have associated autoimmune endocrinopathies, including hypoparathyroidism, hypothyroidism, and hypoadrenalism (autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy [APECED]), which is caused by a loss-of-function mutation of the autoimmune regulator gene, AIRE ; in these patients autoantibodies against interleukin-17 (IL-17) and IL-22 are found ( Chapter 212 ).