[An evaluation of the terms used in studying the medical problems of population migration and its classification in foci of opisthorchiasis].

On the basis of some epidemiological criteria, the work gives grounds for distinguishing the category of "new settlers" among the whole number of "newcomers". The time necessary for the social adaptation of new settlers is estimated, which makes it possible to take them into account together with permanent residents. The scheme of the division of the population according to the duration of their residence in the endemic area is proposed.