Changing trends in the epidemiology of human brucellosis in California from 1973 to 1992: a shift toward foodborne transmission.

From 1973 through 1992, 426 cases of human brucellosis were reported in California, of which 98% were laboratory confirmed. Brucella melitensis was identified in 185 cases (78.7% of the bacteriologically typed cases). Hispanics accounted for 81% of the cases from 1983 to 1992 compared with 65% during the previous decade (P < .01). The population-adjusted average annual incidence was higher in Hispanics, especially in children and teenagers, compared with non-Hispanic whites and African Americans. Slaughterhouse cases decreased from 25% during 1973-1982 to < 3% during the following decade. Changes in case distribution were characterized by a decreasing incidence in the Central Valley and an increasing incidence in the San Francisco Bay area and the southern Coast Range. Hispanics were more likely to report being infected by consumption of milk and cheese in Mexico during 1983-1992 than during the previous 10 years (relative risk, 1.45). Between 1973 and 1992, human brucellosis in California evolved from an occupational to a foodborne illness.