Tracking Trichophyton tonsurans through a large urban child care center: defining infection prevalence and transmission patterns by molecular strain typing.

OBJECTIVES: Trichophyton tonsurans is the single most common cause of pediatric dermatophytoses in North America and is observed with increasing frequency in other countries. This investigation was designed to gain insight into the natural course of T. tonsurans infection. PATIENTS AND METHODS: This 2-year prospective, longitudinal study evaluated all preschool-aged children attending a single child care center. Scalp cultures were collected monthly from each child in attendance, and the presence of disease symptoms recorded at each visit. Dermatophyte genotype was assigned based on the combination of stable sequence variations (2 length variants, 8 single-nucleotide polymorphisms, a 10-base pair insertion, a 14-base pair deletion) present in 2 gene loci.
RESULTS: A total of 3541 scalp cultures were collected from 446 children during 24 months. Twenty-two percent to 51% of scalp cultures per month were positive, contributing 1390 fungal cultures of which 1048 were typeable. Among children with multiple typeable isolates, 51% exclusively carried the same strain, 37% demonstrated a single predominant strain with secondary strains transiently acquired, and 12% harbored a different strain of T. tonsurans with each typeable culture. The probability that the same strain persisted in subsequent months was 0.898 and unlikely to have arisen by chance. Rates of symptomatic disease were significantly different between exclusive, predominant, and transient carriers of T. tonsurans.
CONCLUSIONS: In contrast to dermatophyte infections in older individuals, where symptomatic disease seems to be a consequence of pathogen acquisition and carriers can be traced to an index case, in this preschool-aged population infection was endemic, and symptomatic disease seemed to represent activation of a single strain that persisted on the scalp.