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Candida species are yeast forms that are ubiquitous in nature and frequent colonizers of the skin and mucous membranes in humans, although they rarely cause invasive disease in immunocompetent individuals. Only a small number of the more than 150 species of Candida that have been described are considered to be pathogenic. Candida albicans remains the most frequent cause of human candidiasis, but infections owing to other species of Candida are increasingly recognized.1-4 In addition, the incidence of infections owing to C albicans isolates that are resistant to azole antifungals is increasing. This changing epidemiology has implications for appropriate treatment of antifungal-resistant Candida infections.

Non-albicans species known to cause human disease include C glabrata, C guilliermondii, C keyfr (formerly C pseudotropicalis), C krusei, C lusitaniae, C parapsilosis, and C tropicalis. Candida parapsilosis is the non-albicans species isolated most commonly in children, and in some neonatal units has surpassed C albicans as the most commonly isolated Candida species.1,4-8 Clinicians should be aware of echinocandin resistance with C parapsilosis. Candida glabrata is the second most commonly isolated species in adults, which also has important implications for treatment, as C glabrata exhibits variable resistance to azole antifungals. Candida tropicalis may be an emerging pathogen in immunocompromised hosts, in whom it is associated with significant morbidity and mortality.9

The incidence of colonization with Candida spp depends upon host characteristics such as age and overall health. Neonates are frequently colonized with Candida spp, and localized oropharyngeal candidiasis (thrush) is not uncommon in this population. Hospitalized and ill children are more frequently colonized than are healthy children. Candida spp have relatively low virulence factors compared to other organisms, and therefore rarely cause disease in the normal host. For candidiasis to occur, the host must have impaired resistance to disease, the number of yeast organisms must be high, or both.

Neonates and pregnant women have impaired host resistance to Candida species, as do patients with immunodeficiencies (congenital or acquired), induced immunosuppression (eg, owing to chemotherapy or corticosteroids), or debilitation (owing to trauma or surgery). Advances in health care that have decreased mortality for many conditions (eg, prematurity and malignancy) have been associated also with changes in host defense and normal flora, which have in turn led to a larger population at risk for invasive Candida infection. Preterm newborns and oncology patients frequently receive multiple and long-term courses of medications, particularly antimicrobials (altering the normal flora), and have defects in mucosal or skin barriers (eg, owing to intravascular catheters), which puts them at high risk for development of candidiasis.

In recent years, Candida species have become increasingly important causes of health-care-associated infections. Most health-care-associated pediatric fungal infections are candidemias, and these are most frequently diagnosed in children in neonatal and surgical intensive care units. The source of transmission in these cases is frequently unclear, although recent studies using molecular diagnostics have ...

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