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Modes of HIV Transmission UNAIDS by mikeholy


									Modelling the expected distribution
       of new HIV infections
        by exposure group

          • To understand the sources of new HIV
            infections and the importance of each

          • To use this information for program

2007 en                                             2

          The spreadsheet uses
             • the current prevalence of HIV infection
             • numbers of individuals with particular exposures, and
             • the rates of these exposures

          to calculate the expected incidence of HIV
          infection over the coming year

2007 en                                                                3
  Major modes of transmission of HIV in adults

          • Sexual contact
            – Commercial sex
            – Casual sex
            – Marital sex
            – Men who have sex with men

          • Injecting drug use
          • Blood transfusions
          • Medical injections

2007 en                                          4
     New infections from sexual transmission

          • New infections = f (HIV prevalence in
                                partners, number of
                                partners, acts per partner,
                                transmission probability
                                per act, STI co-factors,
                                condom use)

          • Protection    =     condom use

2007 en                                                       5
     Probability of HIV Transmission (sexual)

          I = S [ 1- { pB[1-β´ ]α(1-ν) + p(1-B)[1-β]α(1-ν) + (1-p) }n ]
             S = Number susceptible
             p = HIV prevalence in partners
             B = prevalence of STIs in partners
             β   =   probability of transmission (with STI (β´), without STI (β) )
             α   =   contacts per partner
             ν   =   proportion acts protected by condom use
             n   =   number of partners

2007 en                                                                              6
          Probability of HIV Transmission (IDU)

            I = S [ 1- { p [1-β ]α(1-ν) + (1-p) }n ]

           p = HIV prevalence in needle sharing partners
           β = probability of transmission
           α = contacts per partner
           ν = use of sterile needles
           n = number of partners

2007 en                                                    7
 New infections from unsafe medical injections

• New infections = Population * [1 – (1 – Ps * Pt * Pc)n]
               Ps   =   Prevalence (total population)
               Pt   =   Transmission probability
               Pc   =   prevalence * % unsafe needles
               n    =   number of injections per year

• Protection        = % unused or sterile needles

2007 en                                                 8
          New infections from blood transfusions

          • New infections = number of unscreened
                             units transfused
                            * HIV prevalence
                            * (1 – HIV prevalence)

          • Protection    = percent of units screened

2007 en                                                 9
                             Data needs
          Population sizes
          HIV prevalence
          STI prevalence
          Number of acts
          Number of partners
          Percent protection
          Transmission probability

2007 en                                   10
                             Data needs
          Population sizes           Surveillance, MOH statistics

          HIV prevalence             Surveillance

          STI prevalence             Special studies

          Number of acts             BSS

          Number of partners         DHS, BSS

          Percent protection         DHS, BSS, service statistics

          Transmission probability   Literature

2007 en                                                             11
          Distribution of infections
                           Injecting Drug Use (IDU)
                           Partners IDU
                           Sex workers
                           Partners of Clients
                           Female partners of MSM
                           Casual heterosexual sex
                           Partners CHS
                           Low-risk heterosexual sex
                           No risk
                           Medical injections
                           Blood transfusions

2007 en                                                14
                   Blood transfusions
                   Medical injections
                              No risk
            Low-risk heterosexual sex
                       Partners CHS
             Casual heterosexual sex
Risk group Female partners of MSM
                   Partners of Clients
                         Sex workers
                        Partners IDU
             Injecting Drug Use (IDU)

                                         0   5   10   15             20   25   30   35

  2007 en                                                                            15
            Priority populations and programs
Route             Population                        Intervention
Sex work          SW and clients                    Out-reach, condoms, STI Treatment

Casual sex        Youth, military, truckers, etc.   Out-reach, condoms, STI

Low risk          Married couples                   Promote testing
IDU               IDU                               Risk elimination, harm reduction

MSM               MSM                               Out-reach, condoms, STI Treatment
Injection         Patients                          Sterile needles

Blood             Transfusion recipients            Screening

Mother-to-child   Pregnant women                    PMTCT

2007 en                                                                                 16

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