Complement-fixation tests employing an egg-yolk sac antigen of R. burneti (American Nine Mile strain) were performed on sera from 1,433 packinghouse workers at Fort Worth, Texas. Evidences of previous infection with R. burneti were obtained. Antibody titers of 8 or more were found in 8.0%, 16 or more in 5.6%, 32 or more in 2.2%, and 64 or more in 1.2%.
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Strauss et al. (1948) studied this question.