[Passive hemagglutination test for individual or epidemiologic diagnosis of human brucellosis].

Coupling of an extract from B. abortus strain 99 to sheep red blood cells by chromium chloride allowed to develop a highly specific and reliable passive hemagglutination test (H). Indeed, H was positive in 99.8 per cent sera from 968 known Brucella-infected heifers, while tube agglutination revealed only 59 per cent and complement fixation 90.9 per cent positive cases. H was positive in 153 sera from 778 proven or suspected human brucellosis where agglutination and/or complement fixation tests were positive, and in 21 sera negative to conventional tests. H demonstreated remote or undiagnosed human B. abortus infections in 28.6 per cent of 18 367 human sera randomly examined in a rural area. Therefore, a simple easy-to-perform passive hemagglutination test could replace a battery of conventional tests for the diagnosis of individual brucellosis, and epidemiologic surveys. The present study points to a high prevalence of undiagnosed brucellosis in man, specially in those area where cattle are raised.