title: Impact of viral load and the duration of primary infection on HIV transmission: systematic review and meta-analysis.
abstract: OBJECTIVE
  HIV 'treatment as prevention' (TasP) describes early treatment of HIV-infected patients intended to reduce viral load and transmission. Crucial assumptions for estimating TasP's effectiveness are the underlying estimates of transmission risk. We aimed to determine transmission risk during primary infection, and describe the relation of HIV transmission risk to viral load.
  
  
  METHODS
  A systematic review and meta-analysis.
  
  
  METHODS
  We searched PubMed and Embase databases for studies that established a relationship between viral load and transmission risk, or primary infection and transmission risk, in serodiscordant couples. We analysed assumptions about the relationship between viral load and transmission risk, and between duration of primary infection and transmission risk.
  
  
  RESULTS
  We found 36 eligible articles, based on six different study populations. Studies consistently found that higher viral loads lead to higher HIV transmission rates, but assumptions about the shape of this increase varied from exponential increase to saturation. The assumed duration of primary infection ranged from 1.5 to 12 months; for each additional month, the log10 transmission rate ratio between primary and asymptomatic infection decreased by 0.40.
  
  
  CONCLUSIONS
  Assumptions and estimates of the relationship between viral load and transmission risk, and the relationship between primary infection and transmission risk, vary substantially and predictions of TasP's effectiveness should take this uncertainty into account.
authors.affiliation: aInstitute of Social and Preventive Medicine (ISPM), University of Bern bDepartment of Infectious Diseases, University Hospital Bern, Bern, Switzerland cDepartment of Infectious Diseases, University of Dakar, Dakar, Senegal dSchool of Public Health and Family Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Nello
authors.initials: N
authors.lastname: Blaser
authors.forename: Celina
authors.initials: C
authors.lastname: Wettstein
authors.forename: Janne
authors.initials: J
authors.lastname: Estill
authors.forename: Luisa Salazar
authors.initials: LS
authors.lastname: Vizcaya
authors.forename: Gilles
authors.initials: G
authors.lastname: Wandeler
authors.forename: Matthias
authors.initials: M
authors.lastname: Egger
authors.forename: Olivia
authors.initials: O
authors.lastname: Keiser
mesh_terms: D018562:Disease Transmission, Infectious / Q000706:statistics & numerical data*; D005191:Family Characteristics; D015658:HIV Infections / Q000635:transmission* / Q000821:virology*; D006801:Humans; D018570:Risk Assessment; D013997:Time Factors; D019562:Viral Load