The mortality from tsutsugamushi disease (scrub typhus) in Niigata and Akita and Yamagata Prefectures in northern Japan, used to be high. Although it differed widely in the basins of the five rivers of the area, it was still much higher everywhere than in Formosa, the Philippines, the rest of South Asia and the South Sea Islands. This is probably due to differences in strain specificity and virulence. Since 1948, owing to the wide application of chemotherapy, the mortality from this disease in northern Japan has been reduced remarkably, and since 1952 no deaths have been reported.
The mortality is highest in children and old people. Males are attacked more frequently than females, but women have a higher case fatality rate than men. In northern Japan, cases are most frequent during July, August and September. Death occurs frequently between the tenth and fifteenth day, being most frequent on the thirteenth day.