Until 1990, Asian Americans represented an ethnic minority group that was perceived to be at lower risk than African Americans or Hispanics/Latinos for HIV infection, the presumed causal agent for AIDS. Reasons cited for this perception include behavioral differences in intravenous drug use, sexual behavioral habits, and underidentification of AIDS cases. However, in urban areas such as San Francisco, Toronto, New York, Boston, Los Angeles, and Seattle, where Asians have immigrated and settled in large numbers, cases of HIV infection and AIDS have begun to increase dramatically, perhaps reflecting the rise in the number of AIDS cases in Asia. In 1994 the World Health Organization estimated the number of adult HIV infections in East, Southeast, and South Asia at 3 million, compared to 1 million in North America.