Detection of antibodies to Afipia species by the microagglutination test

A microagglutination test with heat-killed, safranin-stained whole-cell antigen for detecting antibodies to Afipia species has been developed. An upper limit of the normal titer of antibodies to Afipia species was found to be > 10 by testing 430 sera. Therefore, a titer of 20 can be considered the lowest titer suggestive of infection. Overall, 5-7% of the sera were positive for Afipia felis, 3% were positive for Afipia broomeae and 11% were positive for Afipia clevelandensis. The frequency of sera positive for unnamed Afipia genospecies 1-3 was < 1%. The agglutinating antibodies belonged mainly to the IgM class.