B. henselae is the principal etiologic agent of CSD, although other Bartonella species may rarely be involved. Consistent with the disease's name, contact (being scratched, bitten, or licked) with apparently healthy cats, and especially with kittens, is the primary source of infection. Adults are affected nearly as frequently as children. In the United States, the estimated incidence is ~10 cases per 100,000 population.