2561
The differences of percentages for HIV - 1 infection in intravenous drug users ( IVDU ) were 67 . 7 % and in non IVDU were 3 . 8 % with a significant statistical difference ( chi 2 = 557 . 5 ; p < 0 . 0001 ) .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
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