NEW ORLEANS - The annual incidence of tinea capitis dropped dramatically during 1998-2007, at least in Northern California.
The incidence among children enrolled in Kaiser Permanente of Northern California was 1.3% in 1998 and again in 1999 before it began a steady decline, culminating in an incidence of 0.3% in 2007, Dr. Paradi Mirmirani reported at the annual meeting of the American Academy of Dermatology.
Her retrospective, population-based study included all Kaiser members younger than 15 years, with an average of 672,373 children per year. Some 70% of all cases of tinea capitis were diagnosed after age 5 years, noted Dr. Mirmirani of the Permanente Medical Group in Vallejo, Calif.
As in numerous other studies, the highest rates of tinea capitis in the Kaiser study occurred in black children. They were also the group with the sharpest decline during the 10-year study period. The incidence of tinea capitis in black children was 450 cases per 10,000 in 1998, plunging to about 200 per 10,000 by 2007.
The incidence declined significantly in all other ethnic groups as well, but those declines started from far lower baseline rates of 75-130 cases per 10,000 in 1998.
"That's quite a dramatic decrease. Maybe we're doing something right," commented session chair Dr. Richard L. Gallo, professor of medicine and pediatrics and chief of the division of dermatology at the University of California, San Diego.
Dr. Mirmirani said that girls had a significantly lower incidence than did boys (1.1% vs. 1.6%). Trichophyton tonsurans remained the predominant causative organism, as has been the case across the United States for decades. T. tonsurans accounted for 89% of all positive cultures at Kaiser in 1998, and 92% in 2007, Dr. Mirmirani continued.
The incidence of tinea capitis in Northern California showed no clear correlation with population density. Although the highest rate was seen in San Francisco County (the most population-dense county), the second-highest rate was in Solano County, which ranked only seventh in terms of population density.
Rates of coexisting atopic diseases in kids with tinea capitis were similar to those reported in the general population. In all, 16% of Kaiser patients with tinea capitis had a coexisting diagnosis of atopic dermatitis, 20% had asthma, and 15% had allergic rhinitis.
The big question, Dr. Mirmirani noted, is why the incidence of tinea capitis in 2007 was less than one-quarter the rate 10 years earlier. There are several possible explanations. For example, the number of new prescriptions for fluconazole and terbinafine rose significantly in the Kaiser system during the study years, while prescriptions for griseofulvin correspondingly declined. It's possible that the increased use of newer antifungal agents contributed to the fall in tinea capitis during 1998-2007.
It's also possible that since the late 1990s, dermatologists have done a better job of educating pediatricians and family physicians (the first-line physicians in dealing with dermatophyte infections) regarding recognition and treatment of cases of tinea capitis and carriers, she added.
Dr. Mirmirani observed that although T. tonsurans is the predominant pathogen today, it wasn't always so. In the 1940s and 1950s, it was Microsporum audouinii, an easier-to-diagnose organism that causes a more inflammatory infection and is visible by Wood's lamp.
"It seems like there's a constant tug of war between host and fungus, a bit of a cat-and-mouse game that causes the causative organism to evolve," the dermatologist said.
Her study was funded by the Kaiser Permanente division of research. Dr. Mirmirani declared having no relevant financial relationships with industry.