Author(s): Van Anh Thi Nguyen 1 , * , Marc Choisy 2 , Duy Hung Nguyen 3 , Thanh Hoa Thi Tran 1 , Kim Lien Thi Pham 1 , Phuong Thao Thi Dinh 1 , Jules Philippe 1 , Thai Son Nguyen 4 , Minh Ly Ho 1 , Sang Van Tran 5 , Anne-Laure Bañuls 2 , Duc Anh Dang 1
According to the World Health Organization (WHO) report in 2010, Vietnam ranked 12th among the 22 highest tuberculosis (TB) burdened countries in the world and 3 rd after China and the Philippines in the western Pacific region , with 290,000 cases of all forms and 32,000 deaths reported in 2010 (WHO tuberculosis country profile). Although Vietnam was among the first few nations in Asia to achieve the WHO targets on case detection rate as well as direct observation treatment short-course (DOTS) coverage and cure rate (report from the National TB program in 1997 and WHO), there was no evidence of decrease in TB incidence during the following decade .
Extensive molecular studies on M. tuberculosis , the causative agent of TB, have revealed a high level of genetic diversity. Interestingly, the genotypes of the circulating strains vary greatly from population to population , , , , . Such geographical differences are likely the result of both the history of M. tuberculosis spread and differences in population-specific transmission capacity of the different strains . Molecular epidemiology studies and routine molecular typing are highly useful for TB control in a given area because they allow to identify recent transmission, populations at risk and risk factors for TB transmission .
In Vietnam, the estimated detection rate poorly reaches 54% (WHO tuberculosis country profile, 2009). The vast majority of the detected cases are hospital-registered patients. This indicates that a large proportion of patients would not be included in the samples of studies based only on hospital-registered patients. A bias is thus expected given that TB patients who come to hospitals generally do so because of severe symptoms. Since there are evidences for phenotypic differences (including virulence) in M. tuberculosis isolates of different genotypes , we can expect the genetic assemblage of the isolates from hospital patients to be different from those isolated from patients found by active case detection in the population.
In this study, we aimed at characterizing the genotypic composition and diversity of M. tuberculosis isolates in the northern plain of Vietnam and at investigating how they are affected by sampling. To this purpose, we used two sample sets collected from the northern plain of Red river delta, one of the most densely populated regions in Vietnam. The first one includes isolates passively collected from hospitals in Ha Noi and Ha Tay provinces, whereas the second one includes isolates from an active screening for TB patients in the general population in Hung Yen province. These provinces are proximate and defined according to the pre-2009 administrative divisions. In the analysis we corrected for a possible confounding location effect by...