Fungal Infections

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98 Fungal Infections

Fungi are one of the four major groups of infectious organisms, along with viruses, bacteria, and parasites. They are divided into two morphologic forms, yeasts and molds. Yeasts are unicellular organisms, usually round or oval in shape, that reproduce by budding. In contrast, molds are multicellular organisms composed of hyphae, or tubular structures that grow by extension or branching. Fungi that grow as yeast and mold forms are termed dimorphic fungi. Molds also grow by spore formation. In addition to morphologic characteristics, biochemical and molecular assays of fungi are used in laboratory diagnosis to help identify genus and species.

The extent of disease caused by fungal exposure is related to a number of factors, including fungal virulence, inoculum size, and most importantly, the host immune system. The majority of clinically significant fungal infections occur in patients whose defense against infection is either compromised or immature. Dermatophytic infections are an exception and occur in healthy children. Examples of host defense compromise include breaches to the normal skin defenses, such as burns or central catheters, children with decreased neutrophil number (chemotherapy) or function (chronic granulomatous disease), and defects in T-cell functioning (severe combined immunodeficiency or HIV/AIDS). Premature infants comprise another group with increased risk of fungal infections, especially those weighing less than 1000 g because of immature immune function and the complexity of their care, often requiring medical devices.

This chapter discusses the three most clinically significant fungi in childhood—Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. Each section contains a brief description of the pathogen, clinical manifestations in the immune competent and immune compromised host, diagnosis, and treatment. Finally, there is a discussion of common dermatophytic infections.

Candida Albicans

Candida spp. are yeasts that are ubiquitous in the environment. C. albicans, the most common species causing disease in children, is a dimorphic fungus that can be grown in both yeast and hyphal forms, which aids its ability to survive in varied environments, including host tissues. Other species isolated from children include Candida tropicalis, Candida parapsilosis, Candida glabrata, Candida krusei, and Candida guilliermondii. Nearly 60% of individuals can be colonized with C. albicans without symptoms, most commonly in the vaginal and gastrointestinal (GI) tracts. Pregnancy, a state of relative immune compromise, increases the vaginal colonization rate from less than 20% to greater than 30%. Approximately 10% of full-term infants become colonized in the GI and respiratory tracts in the first 5 days of life. The incidence of colonization of infants weighing less than 1500 g can be as high as 30%. Newborn infants can acquire the organism during passage through the birth canal or postnatally. Some forms of locally invasive candidiasis can be found in immune competent children, including vulvovaginitis, laryngeal candidiasis, and chronic draining otitis externa, but usually in the presence of systemic antibiotics. Systemic candidiasis is limited to immune compromised children, including those who are premature.

Clinical Manifestations and Management

Oral candidiasis, also known as oral thrush, is a candidal infection of the oral-pharyngeal mucosa (Figure 98-1). It can affect up to 2% to 5% of otherwise healthy newborn infants and present as early as 7 to 10 days of life. In immunocompetent children, it is most common in infants and presents as adherent white plaques on the buccal or gingival mucosa. Removal of these plaques can result in localized bleeding. It can present with no symptoms or with increased fussiness and decreased feeding. Oral thrush is uncommon in children older than 12 months except after antibiotic use. Without recent antibiotic use, one may consider a primary immunodeficiency, diabetes mellitus, or HIV infection. Pseudomembranous candidiasis can be diagnosed clinically or by the identification of yeast cells and pseudohyphae by Gram stain or potassium hydroxide prep. Thrush can be treated with nystatin applied directly to the oral mucosa for 7 to 10 days. Thrush caused by antibiotic use generally resolves as the offending agent is discontinued. Bottle nipples and pacifiers should be sterilized as well to prevent reinfection.