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