defined by the World Health Organization in 1974 high-risk group WORLD HEALTH ORGANIZATION People who inject drugs World Health Organization major risk factor WHO, 2013 http://www.who.int/hiv/topics/idu/en/ http://www.who.int/hiv/topics/idu/en/ http://www.who.int/hiv/topics/idu/en/ http://www.who.int/hiv/topics/idu/en/ http://www.who.int/hiv/topics/idu/en/ WHO http://www.who.int/hiv/topics/idu/en/ WHO | People who inject drugs