Page 41 - Epidemiological studies on tuberculosis control and respiratory viruses

Main conclusions and implications
By using genotyping data of all cases diagnosed with culture-confirmed TB between October 2003 and December 2008 in the Netherlands, we found that there was a phylogeographical association between patient’s origin and strain lineage. Euro- American lineages were most frequently found among non-clustered native Dutch TB cases and non-Euro-American lineages among recently arrived foreign-born cases with non-clustered M. tuberculosis isolates (most likely to represent importation of foreign genotypes), of whom the majority originated from Asia and Africa. Furthermore, clonal homogeneity, and reduced association of risk factors with clustering was most pronounced among non-Euro-American lineages as compared to Euro-American lineages. Together, these findings suggest a lineage-dependent degree of reliability of the inference on transmission; transmission based on clustering by VNTR typing among recently migrated foreign-born should be interpreted with caution. 24-locus VNTR typing can thus successfully be used as a public health tool to exclude transmission between individuals infected with different genotypes. However, epidemiological data are required to confirm outbreaks or transmission events when genotypes of recently immigrated foreign-born match. Collection of epidemiological data can be difficult and might be hampered by recall bias as TB patients might have been infected by a contact many years earlier, and patients of certain high risk groups, such as drug users, might be less willing to cooperate.
Further research
The clonal and phylogeographical population structure of M. tuberculosis emphasises
the need to continuously monitor the importation of specific strain types in
the Netherlands. With the growing globalization, immigration patterns in the
Netherlands are subject to change, as are the strain lineages predominating in
countries of origin. Characterization of predominant and emerging M. tuberculosis
clones as part of routine surveillance will provide information on the degree of 7 reliability of the inference on transmission for specific strain types.
Whole genome sequencing (WGS) studies will probably improve the discrimination of strains apparently identical by VNTR typing, as WGS has a greater resolution than does VNTR genotyping (6) (7). The combination of field and molecular epidemiology cannot identify who infected whom. In contrast, WGS allows inference about direction of transmission between cases, and could thus identify super-spreaders and predict the existence of undiagnosed cases, potentially leading to early treatment
General Discussion
121