Published ahead of print on August 2, 2007, doi:10.1164/rccm.200702-187OC Am. J. Respir. Crit. Care Med., Volume 176, Number 9, November 2007, 930-935 A more recent version of this article appeared on November 1, 2007
Submitted on February 5, 2007 Impact of Immigration on the Molecular Epidemiology of M. tuberculosis in a Low-incidence CountryUlf R Dahle1*,1 Norwegian Institute of Public Health, Oslo, Norway * To whom correspondence should be addressed. E-mail: ulf.dahle{at}fhi.no.
Rationale: Programs to prevent the incidence rate of tuberculosis (TB) from increasing in many low-incidence countries are challenged by international travelling and immigration from high-burden countries. Objective: The current study aimed to determine the effect of such immigration on the genetic diversity of Mycobacterium tuberculosis isolates in an entire nation's population during 1994-2005. Methods: A total of 3131 patients were notified with TB during the 12 year period. Of these, 2284 (73%) were verified by culture and isolates from 2173 (96%) of these were analyzed by IS6110 restriction fragment length polymorphism. Results: Only 31% of the included strains were isolated from non-immigrants, the remaining 69% were isolated from immigrants. Although the incidence increased throughout the period, the genetic diversity remained high. A total of 135 clusters were identified, the percentage of recent disease was reducing among non-immigrants, and remained stable among the immigrants during the study period. Although 69% of the isolates originated from immigrants from high incidence countries, the established TB control program in the receiving country was dequate for the prevention of disease transmission. On average per year, only 2 nonimmigrants and 13 immigrants developed disease as a result of infection within the country by imported M. tuberculosis. Conclusion: Twelve years of M. tuberculosis importation as a result of immigration from high-incidence countries had little influence on the transmission of this pathogen in the receiving low-incidence country. To prevent future increase of transmission of TB, the current control strategies of low-incidence countries are adequate but must be maintained. Key words: Tuberculosis, epidemiology, fingerprinting, immigrants
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