The urban-to-rural ratio of the prevalence of tuberculous infection summarizes the differences between Korea and Zanzibar.

In Zanzibar, the urban population has a much higher prevalence of tuberculous infection than the rural population.

In Korea, the excess prevalence of infection in the urban population is clearly present, but not as pronounced as in Zanzibar.

These examples suggest that a variation in the prevalence of tuberculous infection might be expected in different countries, depending on the degree of isolation of rural areas.

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