The demographic character of the study participants.

<p>IDUs, intravenous drug users; NS, not significant.</p>a<p>data available for 400 subjects.</p>b<p>data available for 289 subjects.</p>c<p>data available for 391 subjects.</p>d<p>data available for 240 subjects.</p>e<p>data available for 385 subjects.</p>f<p>data available for 242 subjects.</p>g<p>Total number of subjects with known gender.</p>h<p>Total number of subjects with known ethnicity.