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Table 3 Estimates of the amount of disease attributable to recent transmission calculated using the “n-1” method and retrospective clustering with cases up to two years beforehand, using all cases notified within different time periods during 2007–11

From: Mycobacterium tuberculosis transmission in an ethnically-diverse high incidence region in England, 2007–11

Time period Number of cases clustered, excluding the first case Number of cases notified during the study period Number retrospectively clustered with cases up to 2 years previously Number of cases with onset more than two years after the start of the study period % due to recent transmission based on:
“n-1” formula Retrospective clustering
2007–11 734 2159 452 1329 34% (32,36) 34% (31,37)
2007–10 554 1721 302 891 32% (30,34) 34% (31,37)
2007–9 393 1291 156 461 30% (28,33) 34% (30,38)
  1. Numbers in parentheses denote (exact binomial) 95% confidence intervals
  2. Only the cases who had onset two or more years after the start of the study period were used in the denominator for the retrospective clustering percentage