Changes in the prevalence of hepatitis C virus genotype among injection drug users: a highly dynamic process.

Correspondence Figure 1. Comparison of the genotype distribution among injection drug users, over a period of 6 years To the Editor—With great interest we have read the article by van Asten et al. in The Journal of Infectious Diseases [1]. An important aspect of their study is its detailing of the introduction and spread of " new " hepatitis C virus (HCV) genotypes among injection drug users (IDUs). Changes of subtype distributions in a given population were shown, for the first time, by our group several years ago [2]. In that study, it was demonstrated that subtype 1b was the prevailing subtype in the German population until subtype 1a started spreading in the early 1980s [2]. This led to a substantial change of the most prevalent HCV subtype, especially in younger people. To highlight the question of whether this change was a single effect, a multicenter study was performed 2 years ago [3]. In that study, we demonstrated that the epidemiology of HCV genotypes in IDUs is subjected to highly dynamic changes. Profound changes in the prevalence of different HCV genotypes were noted between 1994–1995 and 2000–2001, when large populations of IDUs (n p 144 and , respectively) were com-n p 172 pared. These changes are summarized in figure 1. The introduction of genotypes that were formerly unknown in this risk population (4 and 2a/b) and the ability of these genotypes to establish significant prevalence within a period of only 6 years are remarkable. The theory of 2 independently developing HCV epidemics had been proposed elsewhere [4], because the epidemiology of HCV subtype 3a and other subtypes seemed to be very different between IDUs and non-IDUs. However, there are indications that the dynamics observed among IDUs also influence the genotypic distribution among the entire population of patients. Although subtype 3a was detected nearly exclusively among IDUs in 1994– 1995, ∼45% of patients infected with sub-type 3a had never been IDUs. In the majority of these people, high-risk sexual behavior (HRSB) was the most probable risk factor for acquiring HCV infection [3]. It can be assumed from these data that the higher the prevalence of a certain genotype among the population of IDUs, the higher is the risk of this genotype spreading beyond the boundaries of the IDU scene. This is most probably due to HRSB, which, today, is one of the major risk factors for acquiring HCV [3, 5]. On …