Setting: Department of Infectious Diseases, Rigshospitalet, Copenhagen, Denmark.
Objective: To study the occurrence of tuberculosis (TB) in a cohort of immigrants from a high incidence country during the years following arrival in a low incidence country.
Design: Follow-up analysis in a cohort of 1983 Vietnamese refugees who arrived in Denmark during the period 1979-1982. The civil registration number could be identified for 1936 (98%) individuals from the original cohort. Date of possible death, emigration and the development of tuberculosis were determined by checking the refugees' civil registration number in the National Civil Register and the National Infectious Disease Registry for Tuberculosis.
Results: Tuberculosis notification for the 1936 individuals fell from 1.14% for the first 12 months to a mean of 0.08% per year during the following 5-year period. During the 16 years of follow up, 36 of the refugees developed tuberculosis, of whom 14 (39%) had had abnormal chest X-ray on arrival and 14 (39%) (including one with normal chest X-ray) had been identified as having active tuberculosis through screening on arrival.
Conclusion: Decline in tuberculosis incidence for immigrants is very rapid if the tuberculosis infection rate is low following arrival. With a very limited TB screening programme (chest X-ray on arrival) and a passive diagnosis policy without preventive chemotherapy, it is possible to control tuberculosis among high prevalence immigrants in a low incidence country.