Annual Mycobacterium tuberculosis infection risk and interpretation of clustering statistics. Emerg. Infect. Dis

Several recent studies have used proportions of tuberculo-sis cases sharing identical DNA fingerprint patterns (i.e., isolate clustering) to estimate the extent of disease attributable to recent transmission. Using a model of introduction and trans-mission of strains with different DNA fingerprint patterns, we show that the properties and interpretation of clustering statis-tics may differ substantially between settings. For some unin-dustrialized countries, where the annual risk for infection has changed little over time, 70 % to 80 % of all age groups may be clustered during a 3-year period, which underestimates the pro-portion of disease attributable to recent transmission. In con-trast, for a typical industrialized setting (the Netherlands), clustering declines with increasing age (from 75 % to 15% among young and old patients, respectively) and underesti-mates the extent of recent transmission only for young patients