Molecular analysis of dermatophytes suggests spread of infection among household members.

Dermatophyte infection from the same strains may be an important route for transmission of dermatophytoses within a household. In this study, we used molecular methods to identify dermatophytes in members of dermatophyte-infected households and evaluated variables associated with the spread of infection. Fungal species were identified by polymerase chain reaction (PCR) using primers targeting the internal transcribed spacer (ITS) regions (ITS1 and ITS4). For strain differentiation, fungal DNA was probed with a ribosomal DNA-specific probe (containing ITS1, 5.8S ribosomal DNA, and ITS2) to detect restriction fragment length polymorphisms (RFLPs). Associations between the spread of a dermatophyte infection and fungal/host variables were determined using χ² and logistic regression analyses. Among the 50 households enrolled in this study, 18 included multiple infected members (MIMs). Trichophyton rubrum was the most commonly isolated dermatophyte species, followed by Trichophyton mentagrophyts and Epidermophyton floccosum. Sixteen T rubrum strains (TR-A to TR-P) were identified, with spread of infection detected in 8 MIM households. Factors that were significantly (P<.05) associated with the spread of infection included the presence of strains TR-B or TR-D, a history of concomitant tinea pedis and onychomycosis, and plantar scaling and/or nail discoloration. This study is unique in that it used molecular evidence to demonstrate the association of certain strains with the spread of dermatophyte infection among members of the same household.