30711 - The Most Probable Past, Present, and Future of the...

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The Most Probable Past, Present, and Future of the AIDS Pandemic JAMES (Jim) CHIN MD, MPH Clinical Professor of Epidemiology School of Public Health University of California at
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? ? ? ? Probable Routes of Initial Global Spread of HIV-1 in the 1960s and 1970s
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AIDS
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Who is at Risk of Acquiring or Transmitting HIV Infection?
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Facilitating factors* Protective factors Other STD, especially ulcerative STD Male circumcision – lack of penile foreskin Traumatic sex, “dry” sex Condom use Acute phase of HIV infection (high viral load) Potential future factors – Microbicides, vaccines Factors that can Facilitate or Limit Epidemic Sexual HIV Transmission *Facilitating factors are not co-factors since they are not required for HIV transmission but can “facilitate” or increase the risk of transmission
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The Reproductive Number (R 0 ) of HIV R 0 for HIV via sexual transmission is dependent on: (1)probability a sex partner is infected with HIV [ p ]; (2)probability of HIV transmission per coital act [ r ]; (3)number of unprotected coital acts with different sex partners [ n1 , n2 …] R 0 = ( p x r x n1 ) + ( p x r x n2 )…
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Risk of Sexual HIV Transmission Based on Pattern of Sex Partner Exchange Annual number (Frequency of Exchange) Pattern of Exchange Risk of HIV Transmission Examples 1 or none (No partner exchange) Monogamous or abstinent Zero or close to zero (R 0 <1) Majority of heterosexuals and many MSM Up to dozens (Months to years) Mostly serial Low (R 0 <1) Up to 20% of adults in Western countries Up to dozens ( weekly to monthly ) Mostly concurrent Moderate to high (R 0 >1) 20-40% of adults in SSA countries and most MSM Up to several hundreds ( Daily to weekly ) Concurrent High (R 0 >1) Direct/ indirect FSW and MSM in small sex networks Up to 1000 or more (Daily) Concurrent Highest (R 0 >1) Large brothel based FSW, MSM in bathhouses
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Question Why is epidemic (R 0 >1) heterosexual HIV transmission almost non-existent in most countries in the world but is so prevalent in sub-Saharan African countries and to a lesser extent in several Caribbean countries and in only a few countries in South and Southeast Asia?
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HIV Prevalence by Wealth Quintiles – Kenya
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Understanding HIV/AIDS Numbers Reported Official Estimated Actual HIV incidence HIV prevalence AIDS incidence
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30711 - The Most Probable Past, Present, and Future of the...

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