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INTRODUCTION

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The genus Malassezia (formerly known as Pityrosporum) includes 14 species, of which 11 are associated with significant human disease (Table 296-1). Skin diseases are the most common manifestation of Malassezia infection. Malassezia species, however, can cause invasive infections, especially in neonates and immunocompromised individuals. Confirmed dermatoses caused by Malassezia species include tinea versicolor, seborrheic dermatitis, and folliculitis.

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TABLE 296-1MALASSEZIA SPECIES ASSOCIATED WITH HUMAN DISEASE
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EPIDEMIOLOGY

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Malassezia species are common inhabitants of human skin, usually found in sebum-rich areas such as the trunk, face, and scalp. Studies on skin colonization have shown that the skin of healthy newborn infants becomes colonized with Malassezia species within the first several months of life. Over 50% of prematurely born infants requiring prolonged hospitalization become colonized with Malassezia species within 2 weeks of life. Ninety to 100% of adolescents and adults have saprophytic skin colonization with Malassezia species. Hospital outbreaks of Malassezia infection have been reported.

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CLINICAL MANIFESTATIONS

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Tinea versicolor is the prototypic skin disease associated with Malassezia. Tinea versicolor lesions are most commonly seen on the chest, back, and upper arms and occur most often in adolescents and young adults. In those who develop tinea versicolor, Malassezia transforms from the yeast phase to the mycelial phase. This results in the characteristic “spaghetti and meatballs” appearance of skin scrapings. Heat, moisture, and skin occlusion favor this transformation. M globosa, M restricta, M sympodialis, and M furfur are the most common causes of tinea versicolor.

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Seborrheic dermatitis due to Malassezia occurs in 2% to 5% of normal hosts. Seborrheic dermatitis is more common among human immunodeficiency virus (HIV)-infected persons, and its prevalence increases to 70% to 80% in individuals with acquired immunodeficiency syndrome (AIDS). This condition varies from thick greasy scales covering the scalp of infants in the first 3 months of life (cradle cap) to an itchy, papular, erythematous, greasy, scaling rash most commonly found in the nasolabial folds, postauricular scalp, eyebrows, or chest. Dandruff, a mildly pruritic scaling of the scalp without associated inflammation, is felt to represent a milder variant of seborrheic dermatitis.

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Folliculitis resulting from Malassezia causes acneiform, pruritic lesions most commonly seen over the shoulders, back, and chest. Lesions present as follicle-limited inflammatory papules or papulopustules that may resemble the lesions of disseminated candidiasis. Malassezia folliculitis is more common in immunocompromised individuals or those receiving broad-spectrum antibiotics or steroids. Discontinuation of steroids or antibiotics is helpful to aid treatment. M furfur is reported to cause eosinophilic pustular folliculitis with pruritus in patients with AIDS, and in its papular form, this lesion is pathologically a ...

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