In1969, Tsukamura (9) divided the species Nocardia asteroides into two species, N. asteroides sensu stricto and N. farcinica. The N. asteroides strains reported in clinical observations are considered to belong to either N. asteroides sensu stricto or N. farcinica. The studies of Berd (10), Holm (11) and Tsukamura (12) showed that the percentage of the real N. asteroides strains is about 50% (Table1). Reported cases of human nocardiosis are summarized in Tables 2, 3, 4 and 5. In contrast to nontuberculous mycobacteriosis, the nocardiosis contains much more patients who have had an immunodeficiency state, and it is suggested that there are more such cases in Japan. The nocardiae are found commonly in the soil and therefore the source of infection to humans is considered to be environment. Both the mycobacteria and nocardiae are found very commonly in our environment. However, the mycobacteria infect humans more frequently than the nocardiae do. This fact suggests that the nocardiae are less virulent to humans than the mycobacteria.
Thus, the nocardiae infect humans more frequently on the basis of immunodeficiency which resulted in the nocardial infection often fatal. Trimethoprim/sulf amethoxazole and minocycline seem to be effective in the treatment of nocardiosis in non-immunodefiency patients.
