Your SlideShare is downloading. ×
  • Like
Mathematical Models to investigate HIV trends in Australia
Upcoming SlideShare
Loading in...5

Thanks for flagging this SlideShare!

Oops! An error has occurred.


Now you can save presentations on your phone or tablet

Available for both IPhone and Android

Text the download link to your phone

Standard text messaging rates apply

Mathematical Models to investigate HIV trends in Australia


This presentation was given at the 2008 AFAO HIV Educators conference.

This presentation was given at the 2008 AFAO HIV Educators conference.

Published in Health & Medicine
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads


Total Views
On SlideShare
From Embeds
Number of Embeds



Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

    No notes for slide


  • 1. Mathematical models to investigate recent HIV trends in Australia David Wilson , Alex Hoare, David Regan, John Kaldor, Matthew Law National Centre in HIV Epidemiology and Clinical Research, University of New South Wales David Wilson , Andrew Grulich, Matthew Law, David Cooper, John Kaldor Implications of the Swiss Consensus Statement [email_address] Reference group: Frank Bowden, Sharon Flanagan, John Imrie, Phillip Keen, Rosemary Lester, Kelly Shaw, Bill Whittaker
  • 2. The Australian HIV Epidemic
    • HIV notifications have been on the rise, particularly in MSM in Victoria and Queensland
  • 3. Objective
    • Attempt to explain
      • causes of the rise in HIV notifications
      • reasons for differences between States
      • focus on men who have sex with men
    • Approach: use a mechanistic mathematical model to represent transmission dynamics
      • combine biological, behavioural, epidemiological and clinical data
  • 4. Data sources
    • Testing rates (Gay Periodic Surveys)
    • Condom usage in penile-anal intercourse (Gay Periodic Surveys)
  • 5. Data sources
    • Number of sexual partners (National Centre in HIV Social Research Reports)
      • Behaviour change
        • Post diagnosis
        • AIDS stage disease
    • Disclosure of serostatus in casual partners (Gay Periodic Surveys)
      • 80-90% in regular partners
  • 6.
    • Treatment if detected in primary infection
    Data sources
    • Treated cases that achieve viral suppression (AHOD; AIDS 2005, 19:179-84 )
  • 7. Structure of mathematical model
  • 8. Other data and assumptions
    • Disease progression between each stage
    • Mortality rates
    • Efficacy of condoms and condom usage with serostatus
    • Average viral load in primary, chronic, AIDS stages, successfully treated; treatment failure
    • Proportion of MSM who have other STIs (5-15%)
      • Increases transmission probability by 2-5 fold
  • 9. Model output
    • Without an increase in other STIs the other changes in behavioural and clinical properties cannot directly account for the increase in National HIV notifications
  • 10. Other STIs
  • 11. Other STIs required
    • Change in other STIs required to describe data
      • ~5-fold nationally
      • ~2-fold NSW
      • ~11-fold VIC
      • ~9-fold QLD
  • 12. Infectious syphilis notifications
  • 13.
    • Unprotected anal intercourse by itself cannot directly account for all of the increased transmission
    • Other STIs as cofactors have played a large role
    • Decreased condom usage may be indirectly responsible for the majority of transmission
    • Promoting condom usage, increasing testing rates, treatment in primary infection, and targeting STIs could be effective interventions
    Conclusions from modelling study
  • 14. Response to the Swiss Consensus Statement: Does undetectable HIV viral load mean non-infectiousness?
  • 15.
    • HIV-positive people on effective antiretroviral therapy are sexually not infectious
      • Completely suppressed viraemia, <40 copies/ml
      • Without other STIs
      • Must adhere to therapy
      • Effects to be evaluated regularly by physician
    The Swiss Statement
  • 16.
    • Potentially unwarranted fear of transmission can be displaced, when the risk is actually small
      • E.g. heterosexual couples attempting conception
      • Another risk reduction strategy for MSM?
  • 17.
    • Potentially large reductions in condom use
      • Leading to increased risk of transmission
      • Further magnified by non-adherence, viral ‘blips’, virological failure, other STIs, missing regular appointment with physician
  • 18.
    • Various prospective and retrospective cohort studies provide evidence to support the statement
      • Serodiscordant heterosexual couples
      • HIV-infected pregnant women
    • There is no doubt that effective treatment lowers the risk of HIV transmission
    Support for the Swiss Statement
  • 19.
    • Study by Quinn et al. (2000) NEJM 342 (13) pp.921.
  • 20.
    • Study by Quinn et al. (2000) NEJM 342 (13) pp.921.
      • Calculated a rate ratio of 2.45 (95% CI, 1.85-3.26) Increase in HIV transmission for every log 10 increase in viral load
      • Mathematically, this translates to
        • chance of HIV transmission per act in chronic infection
          • ~0.0005 for female-to-male
          • ~0.001 for male-to-female
          • ~0.01 for male-to-male
  • 21.  
  • 22.
    • Assuming each sexual act between serodiscordant people is independent of other acts in terms of the chances of HIV transmission, we can estimate the probability of transmission over a partnership of numerous acts for given viral load
    • Consider an ‘effectively treated’ HIV-infected person
      • A viral load of 10 copies/ml
      • In discordant sexual relationship (~100 acts per year)
      • Probability of transmission per year is approx.
        • 0.0021 for female-to-male
        • 0.0043 for male-to-female
        • 0.0425 for male-to-male
  • 23.
    • In a cohort of 100 serodiscordant couples followed for one year, the expected number of seroconversions would be
      • 0.22, 0.43, and 4.3 for F-to-M, M-to-F, and M-to-M
    • The Quinn study observed no seroconversions out of 51 couples followed for less than 2 years
      • This is not surprising from a probabilistic sense
    • However, in a large population and over a long period of time significant numbers of seroconversions would be expected
  • 24.  
  • 25.  
  • 26.  
  • 27.
    • In a population of 10,000 serodiscordant couples, in which the HIV-infected person is ‘effectively treated’, over 10 years (~1000 acts)
    • The expected number of seroconversions would be
      • ~215 for female-to-male transmission
      • ~425 for male-to-female transmission
      • ~3524 for male-to-male transmission
    • HIV transmission in heterosexual partnerships is rare, but non-zero
    • HIV transmission in male homosexual partnerships could be surprisingly high
  • 28.
    • For Australian MSM, on antiretroviral therapy, viral suppression is achieved in ~85% of cases
    • If ~15% of treated cases had an inflated viral load of 1000 copies/ml the expected number of seroconversions would be
      • ~706 after 1 year
      • ~4385 after 10 years
    • Compare: ~104 and ~990 after 1 and 10 years under current conditions
    • Although the individual risk per act is relatively small, the rate of transmission over large numbers of acts is predicted to be substantial
  • 29.
    • Although there is little risk of HIV transmission if ‘effective treatment’ alone is used for prevention, it does not make the Swiss consensus statement a sensible public health message
    • Population-level effects can be harmful, particularly among MSM