Modes of HIV transmission & Prevention of HIV/AIDS
- How have the trends in misconception about HIV/AIDS changed over time?
o Lowered incorrect answers than 1985. More are aware about the actual ways of HIV transmission. Used to think it was from touching toilet, sharing drinks, kissing
- Three reasons why HAART is not the ultimate panacea for HIV/AIDS
- o 1. Potential for multi- drug resistance
- o 2. Important quality of life issues
- o 3. Unattainable/ hard to get
- Three examples of how antiretroviral therapy benefits prevention
- o Therapy reduces MTCT ( mother to child transmission)
- o Past exposure ( PEP) reduces HIV infection from needle stick injuries
- o Reduces viral load, reduces risk of sexual transmission
- How have HIV infection rates in the U.S. changed in the last 25 years?
o High prevalence, lower incidence ( stable), because of better drugs
o What can we attribute the decline in infection in the mid-to-late 1980s?
* New treatments
o Refer to slide Current Challenge in the U.S.; know three potential reasons for the recent increase in infection rates among MSM.
- * Increase in risky behavior
- * Reduced concern with advent of HAART
- * Club drugs
- * Generational forgetting
- From the 1980s to1990s, what group was targeted for prevention efforts? Why?
o General population/ risky population due to stigma, limited testing
- Positive prevention is endorsed by whom? It is consistent with ?
o Joint UN Program of HIV/AIDS
o Know the recommendations for Africa outlined in both the required reading and slides.
- Know the sources of infectious HIV
o HIV is present in which cells?
- * Macrophages
- * T helper cells
- * Lymphocytes
- * Langerhan cells
o Why can HIV be readily transmitted via some bodily fluids (e.g. blood), but not others (e.g. perspiration) ?
* Isolated and not highly concentrated- cells are found in blood/ semen, mucosal lining
o High concentrations of HIV are found in which four bodily fluids?
* Blood, semen, vaginal fluid/ secretions, breast milk
o Is HIV fragile outside of its host?
* Yes, inactivated by exposure to light, contact w/ soap and water
- From an epidemiologic perspective, why do family members of HIV+ hemophiliacs offer a unique opportunity to study casual transmission of HIV?
o They didn�t know about HIV status in the 80�s
- Three modes of HIV transmission:
- 1) Identify the three forms of Blood-to-blood transmission;
- 1. Transfusion of HIV infected blood products
- 2. Needle sharing drug injection
- 3. Accidental needle sticks by healthcare workers
- o What can be done to prevent these routes of transmission ?
- * Sterilization, viral inactivation methods
- 2) Sexual transmission
- o Why is intercourse (vaginal/anal) a good mode of transmission?
- * Site of macrophages, small tears = susceptible to infection
o What is the approximate risk of male to female transmission of HIV?
* 2x � 10x
Reasons why one gender is more susceptible to HIV than the ot
- * Higher concentration of viral load in semen, vagina has more surface area
o Review slide on oral-genital transmission of HIV
- * Lower risk, difficult to estimate because of other sex behaviors/cofactors
- * Cofactors: traumas, ulcers, STI�s, ejaculation in mouth, viral RNA, other oral infections
o Be familiar with the ABC campaign
- * What do the three letters represent?
- * Abstain
- * Be Faithful
- * Condoms
* Understand the debate over Uganda's success; which group(s) claim success is due to A, B, C ?
* A) Religious groups B) British Med Journal, Ugandan Aids Control C) Donors ( WHO, USAID)
* A) Religious groups B) British Med Journal, Ugandan Aids Control C) Donors ( WHO, USAID)
* Why can the concept of �collective efficacy� not be readily promoted in a public-health campaign?
* Requires involvement on every level, including small communities
- 3) Mother-to-child transmission (MTCT) ( Perinatal)
- o Know the three routes of MTCT.
- * Intrauterine/ Antenatal- DURING PREGNANCY
- * Peripartum- DURING LABOR/ DELIVERY
- * Postpartum- BREASTFEEDING
o Are the preventive measures effective for any of the 3 routes of MTCT?
- * Hint: refer to limitations of C-sections and formula replacements
- * C Section reduce risk of transmission- only recommended on high viral load
- * Giving drugs is cost efficient
- * Formula replacements are safe
- o What did the U.S. do in curbing rates of MTCT ?
- * Routine screening
- * Use of antiretroviral drugs
- * Avoid breastfeeding
- Incidence versus Prevalence
- o Which of the two is a measure of risk? And why?
- * Incidence because it tells us current rate of spread/ transmission
- o Prevalence is a function of ���.
- * Thus, does an increase in prevalence of AIDS reflect an increase in the rate of HIV infection (i.e. incident cases of HIV)?
- * No, could be because of better treatments
- * Prevalence higher because living longer
Individual Assessment of HIV Risk
- Know characteristics of the normative model of risk assessment
o Requires accurately defining risks, calculating and choosing alternative w/ highest expected value
o Do we typically make decisions on the basis of normative models, i.e. by applying laws of logic and statistics?
o If not, how do we assess risk from various probabilities?
Heuristics- basic rules of thumb
- Heuristics are useful in making what kinds of decisions?
Quick decision making
o Can the use of heuristics lead to significant biases in decision-making?
* Yes, because there can be consistent patterns to biases
* Know characteristics of the representativeness heuristic
* More object X is similar to class Y, more likely X belongs to Y , ignores multiple biases
* We often judge whether object X belongs to class Y by how representative X is of Class Y
* Identify and understand the two representative biases
- * Misconception of chance
- o Expect random sequences to be representatively random
- * Insensitivity to Base Rates
- o Physicians don�t use it
- o Judge on description rather than if there are more farmers than engineers, etc
o What are the two main contributors to the availability heuristic?
- * Familiarity-frequency of an item or event in our memory
- * Salience- vividness of item or event
o Using the anchoring heuristic, adjustments are typically biased towards which values?
* Toward initial values, the anchor
o Do we tend to overestimate or underestimate conjunctive events? What about disjunctive events?
* Overestimate conjuctive ( multiple steps, this and that) events, Underestimate disjunctive ( multiple possibility, this or that) events
* How do we calculate the two events?
* P ( A * B) = P(A) * P(B) � CONJUNCTIVE
- * P ( A or B) = P(A) + P(B) - DISJUNCTIVE
- * Examples of the two events
- * Birthday paradox � disjunctive
- * HIV ( overestimate needle stick) � conjunctive
o What is the connection between optimistic bias and HIV testing?
- * Optimistic bias occurs when people tend to believe they are less likely than others to experience harm, personal invulnerability
- * = underestimate risk for HIV, happens to other people, can�t happen from sexual contact with good people
- * LATE HIV TESTING
- * Characteristics of the late testers
- * Young ( 18-29 yrs), heterosexual, LESS educated
- young (optimistic bias?), heterosexual (representativeness heuristic ), less educated (knowledge), and African American or Hispanic (representativeness heuristic ).
o Why can HIV prevention heuristics be misleading?
- * Causes condom usage only with casual partners
- * Known partners are safe partners
- * One marriage is safe
- * Trusted partners are safe partners
- * IMPORTANCE IN TESTING ALL COUPLES
HIV Testing & Surveillance
- What are the relationships between the HIV test and antibodies, viral levels and the window period ?
o In the 8 week window period, no antibodies test HIV + ( test comes out false negative)
- Approximately what % of the U.S. population has not been tested for HIV? Does this % vary by ethnicity?
o 42%, YES
- Understand the 2x2 table for screening test outcomes (slide 6)
- o TP FP
- o FN TN
- - Know formulas for sensitivity, specificity, PPV and NPV
- o Sensitivity = TP / TP + FN
- o Specificity = TN/ TN+ FP
- o PPV ( probability of having disease if test is positive, increases with greater disease prevalence, increases with greater specificity of a test, in cases when the disease prevalence is low) = TP / TP+FP
- o NPV ( prob. of having disease given neg. test results) = TN / TN + FN
o What is the trade-off between sensitivity and specificity?
- * Sensitivity = may be more FP
- * Specificity= may be more FN
- What are the two stages in HIV sequential testing?
o #1 ) very sensitive ( ELISA) #2) W Blot: very specific
o Know characteristics of the tests used in both stages
* Less invasive, expensive
* Very specific W Blot
o Sequential testing yields a higher net sensitivity or higher net specificity?
* Higher net sensitivity, lower net specificity
- In what setting are we more interested in predictive values (PPV/NPV)?
o Clinical setting
- Unlike sensitivity and specificity, predictive values are a function of the characteristics of the population
o How does this concept relate to efficiency in screening programs?
* More efficient in populations at greater disease risk
- Rapid/home HIV testing
- o Identify three benefits of rapid HIV testing
- * More get results ( increase receipt of test results)
- * Increases identification of HIV + pregnant women
- * More testing in ER
o Approximately how many U.S. citizens are unaware of their HIV infection?
* 300,000 citizens
o Who are the likely consumers of home HIV tests?
* Affluent consumers, wealthy, worried well, primarily serionegative ( to be sure), new couples, recent high risk exposure ( binge drinkers, one night stand), persons seeking confirmation
o What are the problems with home HIV testing?
- * People who need it most can�t afford it
- * No counselor
- * Lower PPV as a result of lower HIV prevalence
- * Does not detect in the window period
- * More FP + FN, undectected HIV pool is now larger
- * Impede access to care for people who need it most
- Why do we need to use PCR testing of infants born from HIV+ mothers?
o Babies can have mom�s antibodies, chance of FP
- In 2006, the CDC recommended a switch to the opt-in or opt-out testing of individuals in a clinical setting? Opt out
- o Why is one recommended over the other?
- * Less anxious about testing
- * Thought it indicated high risk behavior
- Review the process by which an HIV test is first reported, and then forwarded to local and state health departments
- - Why is HIV/AIDS surveillance so important?
- o Monitor trends
- o Target HIV prevention + treatment
- o Provides data for funding ( Ryan White)
- Compare and contrast confidential versus anonymous HIV testing
Confidential = fake name secretely, Anonymous= no name taken
Global Aspects of HIV/AIDS- Part I
- - What region of the world has the highest concentration of HIV?
- o Sub-Saharan Africa
- o In sub-Saharan Africa, 3 countries bear the brunt of the disease -- Swaziland, Botswana and Zimbabwe. One out of every three
- o adults is infected in these countries.
- Know the global transmission of HIV as described in slide #5
- o US- MSM, - moved into drug using population
- o Sub-Saharan- heterosexual sex
- o SE Asia, India, China, Former Soviet Union- brothels, prostitution, IV drug users, male drug users infected female sex workers
- Know potential explanations for variation of HIV prevalence throughout Africa.
- o Why is HIV prevalent in sub-Saharan Africa?
- * Sex partners ( debunked), High Risk, Low mix Theory, Long term, concurrent sexual relationships
- * Prostituion -> migrant workers -> general population
o Understand concept of concurrent, �transactional� relationships
- * Sex from boyfriends for gifts
- * Could be riskier than prostitution
o Why is HIV less prevalent in West and North Africa?
* Circumcision, monitoring sexual behavior
- What is the distribution of HIV/AIDS by gender, stratified by region?
- o Children- 6%, Men- 49%, Women-45%
- o Worldwide prevalence, prevalence in sub-Saharan Africa, prevalence outside of sub-Saharan Africa
- Explanations for why women have a higher prevalence of HIV than men
- o Nature of transactional/ polygamous relationship
- * Fewer men in sexual network
- * Older men have more economic resources
- * Women have limited say and social power
- * Prostitie -> migrant workers -> spouses
- * Biological factors- women are more vulnerable to heterosexual transmission
- * Virgin myth
- What is HAART?
- o Highly Active Anti-Retroviral Therapy -> slows rate at which virus multiples
- o Typically includes 3 drugs from at least two different classes
- * Protease inhibitors
- * Reverse transcriptase inhibitors nucleoside and/or non-nucleoside
- Why do we consider Brazil's response to HIV/AIDS a success story?
- o Mid 1990�s. 1% or about ? million people were HIV+
- o Built AIDS clinics, but couldn�t afford to fund HAART
- o Suit bought against government for access to the antiretroviral drugs
- * Brazil passed law guaranteeing access to HIV drugs to all citizens who need them
- * Generic drugs
- * Pharmaceutical companies engage in R&D to exchange for patent privileges
- o With limited resources, how did their government obtain expensive HIV drugs?
- * They made generic HIV dtugs
- o Is treatment cost-effective in the long-term? Yes, 40-80% decrease in morbidity/ mortality
- * 85% decrease in hospitalization
- o How does Brazil's response contrast with how the South African government dealt with HIV?
- * Limited prevention- only approach, denial of HIV/AIDS
* As a consequence of their policies, what has happened to South Africa's life expectancy?
Dropped to less than 50
* What age group in South Africa has been disproportionately affected by HIV/AIDS?
- What did Thailand do in the early 1990s to control the spread of HIV?
- o Condom campaign
- - Review importance of healthcare infrastructure for treating HIV patients
- o Critical need for labs, equipment and well trained personnel
o Distribution of HIV drugs without proper care/instructions can lead to �..
* Multidrug resistance- because of failing to adhere to regimen
Living with AIDS: Individual and Societal Issues
- - Review debate of individual rights vs. public health in the decision to close bathhouses in San Francisco
- o Thought it was an antigay movement (public comndemnation of style)
- o Delayed closing of public baths
- o Opposition to informational brochures in the bathhouse
- o Delayed full articulation of transmission modes
- What governments have been slow in accepting the reality of HIV/AIDS?
- o South Africa, USA
- - What is the pertinence of the Americans with Disabilities Act (1990)?
- o disability is defined as a physical and mental impairment
- o no discrimination in public goods, etc, ( jobs, etc)
- - How has the perception of HIV/AIDS as an urgent health problem in the U.S. changed over time?
- o Gone down- decreased as an urgent problem, 44% in 95 to 17% in 06
- - Do most people today feel that the U.S. government spends too little or too much on HIV/AIDS?
- o Too little- 63%
- o What is the perception in relation to other diseases?
- * too low- compared with cancer and heart disease- 48%
- o Using a crude measure, such as expenditures/death, how does HIV/AIDS compare to other diseases?
- * More expensive , spend more but more deaths
- - Contrast the public's view on U.S. foreign spending (in general) versus U.S. foreign spending on HIV/AIDS
- o 62% think that we spend too much on foreign aid in general, but 60% think we�re responsible to spend money for HIV worldwide
- o Has our view on foreign spending on HIV/AIDS changed over time?
- * Increased from 44% in 02 to 60% in 06
o What country contributes the greatest share to international AIDS assistance?
* US at 40.3%
- Review the Ryan White CARE Act (1990)
- o Treatment to those that can�t afford it
- o Comprehensive AIDS Resource Emergency
- o In 1990, the act passed Congress ( vote: 402 to 4)
- o It is the United States largest federally funded program for people living with HIV/AIDS
- o Goal is to improve availability of care for those ( HIV+) with low income
- o Payer of last resort
- Review explanations for why women are especially susceptible to contracting HIV (note: some overlap with prior lecture)
- o Biological- more virus in semen
- o Forced to enter into sex work and/or barter sex for food, shelter and safety
- o Sex workers at high risk for infection
- * Can�t negociate with clients who refuse to wear condoms, especially if work is illegal
- * Little choice
- * Rape, sexual slavery
- * Culture- men to have multiple extramarital relationships
- * Cultural norms may deny women knowledge of sexual health
- * Social pressure to bear children
- * Women may be unaware of or unable to discuss male partner�s HIV risk
o Why are public health advocates particularly hopeful of the vaginal microbicides?
- * Can be used without male partner consent
- * Useful when can�t be used, IE when sex workers is covert ( secret, ninja)