Several explanations may account for the absence of an initial steep decline in incidence rates. First, the proportion of immigrants who were recently infected or reinfected may already have been low at the time of immigration. Next, the risk of reactivation of latent tuberculosis infection in these immigrants may have been higher than previously modeled in white nonimmigrant populations (8,9). Finally, immigrants residing in the Netherlands may have acquired new infections or reinfections, either through transmission within the Netherlands or through frequent visits to their country of origin. DNA fingerprinting data suggest that transmission within the Netherlands may indeed have occurred, although it is not the key factor; in a recent study, infections.
