title: Multiple HIV-1 introductions into the Swedish intravenous drug user population.
abstract: In 2001, an increase of HIV-1 diagnoses among intravenous drug users (IVDU) was reported in Sweden. In nearby countries, Finland, Russia and the Baltic states, recent outbreaks had been described. Since there was a concern that these outbreaks would carry over to Sweden a study was initiated to determine the factors leading to the Swedish increase of HIV-1 diagnosed IVDUs. HIV-1 env V3 sequences were obtained from 97 patients enrolled in ongoing epidemiological studies encompassing the years 1987--2004 with a focus on 2001--2002. The sequences were used for maximum likelihood and Bayesian inference of the molecular epidemiology. Among the virus spreading in 2001--2002, we found that four different subtypes/CRFs were present in the Swedish IVDU population (A, B, CRF01_AE and CRF06_cpx). Subtype B constituted 85% of the infections, established by 12 independent introductions into the IVDU population. The worrisome increase in 2001 was mainly not a result of import of the outbreaks in nearby countries, but rather a higher detection rate of secondary cases due to efficient epidemiological tracing of the generally slow spread of established forms of subtype B in the IVDU community. However, a few of the non-subtype B cases were linked to the outbreaks in Finland, Estonia and Latvia. Because HIV-1 outbreaks can easily be exported from one country to another amongst IVDUs, this prompts continued surveillance in the Baltic Sea Region.
authors.affiliation: Department of Virology, Swedish Institute for Infectious Disease Control, SE-17182 Solna, Sweden.
authors.forename: Helena
authors.initials: H
authors.lastname: Skar
authors.forename: Staffan
authors.initials: S
authors.lastname: Sylvan
authors.forename: Hans-Bertil
authors.initials: HB
authors.lastname: Hansson
authors.forename: Olle
authors.initials: O
authors.lastname: Gustavsson
authors.forename: Hans
authors.initials: H
authors.lastname: Boman
authors.forename: Jan
authors.initials: J
authors.lastname: Albert
authors.forename: Thomas
authors.initials: T
authors.lastname: Leitner
mesh_terms: D005060:Europe / Q000453:epidemiology; D005260:Female; D015658:HIV Infections / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D015497:HIV-1 / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D017720:Molecular Epidemiology; D010802:Phylogeny; D015203:Reproducibility of Results; D015819:Substance Abuse, Intravenous / Q000453:epidemiology* / Q000821:virology*; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors