[Present status of studies on epidemiology and molecular epidemiology of Mycobacterium kansasii, in special reference to its epidemiology].

Mycobacterium kansasii, a slow-growing photochromogen, causes serious pulmonary diseases in humans. Since the 1980s the isolation rate of M. kansasii has been surpassed by that of Mycobacterium avium complex (MAC). Pulmonary disease caused by M. kansasii is known to be more common in urban areas than in rural areas, and its changing epidemiologic features and geographical distribution have been known for several decades. The disease had been found almost only in and around Tokyo areas until the 1970s, but after the 1990s, the disease spread to the rest of Japan. The incidence rate of the disease due to M. kansasii remained at the same level, while non-tuberculous mycobacterioses as a whole are rapidly increasing, especially because of the increase in Mycobacteriu avium complex diseases, and because of the improvement of identification techniques in recent years. This change in the epidemiologic picture of M. kansasii in Japan seems to be influenced by the international trends of this disease. The complicated environmental and other factors related to M. kansasii infection are discussed in this review.