in two phases were measured using an indirectimmunoperoxidaseassay at two reference centers for rickettsiosis in Japan. Cross-reaction was defined as a higher titer against R. typhi in convalescent sera than in acute sera among patients fulfilling the criteria for JSF diagnosis. The frequencies of IgM and IgG were also evaluated. Approximately 20% of cases showed positive cross-reactions
titers against multiple serotypes of and were revealed by indirectimmunoperoxidaseassays. These clinical and serological data, even in the absence of molecular or isolation evidence, provided grade II evidence that this was a concurrent infection of sympatric scrub typhus and Japanese spotted fever.
, the serological cross-reactivity among serotypes is still unclear. We analyzed 1406 cases tested by indirectimmunoperoxidaseassay using seven rickettsial antigens-one and six serotypes-between 2003 and 2016 at two reference centers in Japan. Of these, 167 JSF and 190 ST cases were serologically diagnosed. None of the ST cases had a significant increase in IgM titers against . Six JSF cases showed IgG