Occurrence of rickettsiosis of spotted fever group in Chiba Prefecture of Japan.

Acute- and convalescent-phase sera were obtained from a patient with suspected tsutsugamushi disease in July 1987, in Amatsukominato located in the southeastern area of Chiba Prefecture, and showed negative serologic reactions with Rickettsia tsutsugamushi, while the convalescent-phase serum reacted positively with R. montana and a Japanese isolate of spotted fever group rickettsia at IgM and IgG titers of 1:320 and 1:640, respectively, in the indirect immunofluorescence test. These findings showed that a rickettsiosis of the spotted fever group occurred also in Chiba Prefecture like in the southeastern areas of Shikoku and Kyushu islands of Japan.