Bug Bytes Volume 4 Number 2 - September 22, 1997
Candidiasis is the term used to refer to the constellation of clinical manifestations associated with infection by any of the more than 150 species of the genus Candida. Candidiasis is now the most common opportunistic fungal infection, and presents in two major forms: mucocutaneous and deeply invasive. Candida are spherical to oblong yeast which reproduce by budding and form chains of elongated forms called pseudohyphae. The ability of C. albicans to form germ tubes when incubated in serum is a useful test allowing for rapid, presumptive identification of this commonly encountered pathogen. Candida glabrata (formerly Torulopsis glabrata) produces neither germ tubes nor pseudohyphae.
C. albicans, the most common cause of candidiasis, is part of the normal flora of the human oral cavity, lower gastrointestinal tract, and vagina. When the complex interrelationships between the normal bacterial flora and Candida are altered on either skin or mucous membranes, Candida may supplant the normal commensal or saprophytic bacterial flora and either colonize or invade tissues. Risk factors for both superficially invasive and deeply invasive candidiasis include diabetes mellitus, immuno-compromised states (human immunodeficiency virus infection or Acquired Immune Deficiency Syndrome [AIDS], granulocytopenia, etc.), prolonged (> 14 days) therapeutic or prophylactic use of broad-spectrum antimicrobials, intravenous hyperalimentation, vascular catheters, and implanted prosthetic devices. Certain risk factors are associated with infection with specific species. Although C. albicans is the most common species recovered from blood, fungemia ! due to C. parapsilosis and C. glabrata is associated with solid tumors and non-malignant diseases. C. tropicalis has a propensity to produce fungemia in granulocytopenic patients. C. parapsilosis is also associated with the use of parenteral alimentation.
Candidiasis most often presents in one of two ways: the Mucocutaneous Syndrome (MS) or the Invasive (deep tissue) Syndrome. The MS includes oropharyngeal (thrush), esophageal, and gastrointestinal (stomach to colon) [GI] candidiasis, intertrigo, vulvovaginitis (the most common form of MS), balanitis, and Chronic Mucocutaneous Candidiasis (possibly the rarest form of MS). While invasive candidiasis of the oropharynx and esophagus occurring in the absence of a predisposing condition should raise the specter of AIDS, invasive candidiasis of the stomach, small bowel, or colon should prompt an investigation for a GI malignancy. Although rare, Chronic Mucocutaneous Candidiasis is of special interest because the often severe involvement of skin and mucous membranes is frequently associated with T-cell dysfunction or endocrinopathies, (ie. hypoparathyroidism or hypoadrenalism). Invasive candidiasis includes candidemia, which may occur with or without solid organ involv! ement, and disseminated candidiasis (including ocular, hepatosplenic, renal, cardiac, and other organ involvement).
Therapy for candidiasis must be tailored to the offending species as well as to the extent and location of the infection. Whereas C. krusei is intrinsically resistant to fluconazole, C. glabrata, C. lusitaniae, and C. guilliermondii display variable resistance to fluconazole. Even relative resistance to Amphotericin B can be seen in C. lusitaniae. MC candidiasis is often treated topically, but may require systemic therapy as in AIDS or Chronic MC candidiasis. However, most cases of visceral candidiasis are due to fluconazole- and Amphotericin B-susceptible C. albicans. Since fluconazole is associated with less toxicity and can be given orally, it is often used first in non-life threatening infections. Because of the ability of C. albicans to bind to a variety of materials used in prosthetic devises and intravascular catheters, a trait held in common with C. tropicalis, candidemia poses an increasingly frequent challenge! to clinicians. The mortality in candidemia is as high as 40% to 60%. In the past it was held that candidemia occurring in an immunocompetent patient with an intravascular catheter could be treated by simply removing the catheter or if catheter removal was undesirable an attempt at catheter sterilization could be tried. Although candidemia therapy remains controversial, a recent consensus statement opines that all patients with candidemia receive some systemic anti-Candida therapy along with, in most cases, removal of intravascular catheters.* There remains some disagreement regarding attempted sterilization of surgically implanted catheters (ie. Hickman and Broviac lines), but if candidemia persists, all catheters, including surgically placed catheters, should be removed.
*International Conference for the Development of a Consensus on the Management and Prevention of Severe Candidal Infections. Clin. Infect. Dis. 1997;25:43-59.