What is the most common cause of tinea capitis in the United States?

Until the mid-1950s, Microsporum audouinii was the most common cause of endemic tinea capitis in the U.S., but it has since been replaced by Trichophyton tonsurans. Several theories have been proposed to explain the almost total disappearance of M. audouinii from the U.S., but the most plausible theory is that it was eradicated by the widespread use of griseofulvin. At the same time that M. audouinii disappeared, T. tonsurans, formerly an uncommon cause of tinea capitis, quickly spread. This species was probably introduced into the U.S. from Central or South America.

Foster KW, Ghannoum MA, Elewski BE: Epidemiologic surveillance of cutaneous fungal infections in the United States from 1999 to 2002, J Am Acad Dermatol 50:748–752, 2004.