A substance or reactant intended to be used together with a parent IVD to perform a specific function in an assay that is used for the qualitative and/or quantitative detection of total antibodies to one or multiple species of the rickettsial bacteria associated with spotted fever in a clinical specimen. Rickettsia species intended to be detected may include Rickettsia rickettsii, R. akari, R. conorii, R. sibirica, R. australis, R. japonica, R. africae, R. honei and/or R. felis.