99 percent of microbes in your body are completely unknown to science

From the abstract: &quot;Analyzing cumulative sequence data from 1,351 blood samples collected from 188 patients enabled us to assemble <i>7,190</i> contiguous regions (contigs) larger than 1 kbp, of which <i>3,761</i> are novel with little or no sequence homology in any existing databases. &quot;<p>I don&#x27;t understand where the &quot;99%&quot; figure in the article comes from.