title: Frequency of HIV-1 dual subtype infections, including intersubtype superinfections, among injection drug users in Bangkok, Thailand.
abstract: OBJECTIVE
  To estimate the frequency and incidence of dual HIV-1 subtype infections, including superinfections, among recent seroconvertors from a cohort of injection drug users (IDUs).
  
  
  METHODS
  A total of 1209 HIV-negative IDUs were followed in a prospective cohort study at 15 methadone clinics in Bangkok, Thailand. After 2308 person-years (PY) of follow-up, 133 seroconverted to HIV-1, of which approximately 20% were subtype B and 80% were CRF01_AE (formerly called subtype E). Specimens from 126 individuals were available at time of first seropositive test and specimens from 80 of these 126 individuals were also available more than 12 months later. For each infected participant, we calculated the amount of time to superinfection, loss to follow-up, or to the closest visit more than 12 months after the time of initial seropositivity.
  
  
  RESULTS
  Of all 126 seroconverters seen at the time of the first seropositive test result, there was no apparent case of concurrent dual subtype infection detected despite 2301 PY of observation. Overall, the incidence of superinfection was 2.2 per 100 PY [95% confidence interval (CI), 0.3-7.8]. The 1-year incidence of CRF01_AE superinfection following subtype B primary infection was 3.9 per 100 PY (95% CI, 0.1-21.9) and the incidence of subtype B superinfection following CRF01_AE primary infection was 1.5 per 100 PY (95% CI, 0.04-8.3).
  
  
  CONCLUSIONS
  Determination of the frequency and incidence of dual HIV-1 subtype infection demonstrates that HIV-1 superinfection is not uncommon in a population with high HIV-1 incidence with more than one circulating strain.
authors.affiliation: Mailstop A-12, National Center for HIV, STD, and TB Prevention (NCHSTP), CDC, 1600 Clifton Road, NE, Atlanta, GA 30330, USA. djh9@cdc.gov
authors.forename: Dale J
authors.initials: DJ
authors.lastname: Hu
authors.forename: Shambavi
authors.initials: S
authors.lastname: Subbarao
authors.forename: Suphak
authors.initials: S
authors.lastname: Vanichseni
authors.forename: Philip A
authors.initials: PA
authors.lastname: Mock
authors.forename: Artur
authors.initials: A
authors.lastname: Ramos
authors.forename: Lily
authors.initials: L
authors.lastname: Nguyen
authors.forename: Thanyanan
authors.initials: T
authors.lastname: Chaowanachan
authors.forename: Frits van
authors.initials: Fv
authors.lastname: Griensven
authors.forename: Kachit
authors.initials: K
authors.lastname: Choopanya
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Mastro
authors.forename: Jordan W
authors.initials: JW
authors.lastname: Tappero
mesh_terms: D005500:Follow-Up Studies; D015658:HIV Infections / Q000453:epidemiology / Q000635:transmission / Q000821:virology*; D006679:HIV Seropositivity / Q000821:virology; D015497:HIV-1 / Q000145:classification* / Q000276:immunology / Q000302:isolation & purification; D006801:Humans; D015994:Incidence; D011446:Prospective Studies; D015819:Substance Abuse, Intravenous / Q000150:complications*; D015163:Superinfection / Q000453:epidemiology / Q000821:virology*; D013785:Thailand / Q000453:epidemiology