Figure 2. Frequency of genotype clusters of tuberculosis, by cluster size (mean 5.68, median 3, range: 2–173), United States, 2005–2009. Frequency was determined by using SaTScan version 9.1.0 (26) on the basis of 3 consecutive, overlapping years: scan A, 2005–2007 (n = 970); scan B, 2006–2008 (n = 1,019); scan C, 2007–2009 (n = 1,128). Error bars indicate upper and lower limits of clusters identified between scan periods.
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