Answers

Exercise 1

1. Kenya

a. There were 22 sites where ANC women were tested in 2001, shown on page 4 of the Fact Sheet. What is the range (e.g., the highest and the lowest) in HIV prevalence among pregnant women reported by these sites?

In 2001, the most recent year for which data is available, HIV/AIDS prevalence among pregnant women attending antenatal clinics (ANC) ranged from 2.0 to 31.0 percent.

b. Is there any evidence that HIV prevalence is higher in urban areas? Explain.

The surveillance data in 2001 give a mixed picture regarding prevalence in urban compared to rural areas. The two major urban sites surveyed in 2001 were Nairobi and Mombasa (see Fact Sheet Annex). In each of these cities, ANC prevalence was approximately 14 percent, a prevalence only slightly higher than the median prevalence (approximately 12 percent) among pregnant women attending clinics in the 20 sites outside major urban areas.

Although sites outside of major urban areas had a slightly lower median prevalence, they had a much larger range in prevalence (from 2 to 31 percent) relative to the two major urban sites.

According to the map of HIV sentinel surveillance in pregnant women on page 5, prevalence appears to be somewhat correlated with population density, that is, areas with higher population density tend to have higher HIV prevalence at ANC clinics than less populated areas. However, other factors such as being on a major transport route also appear to be associated with relatively high prevalence.

c. Use the map on page 5 to describe the geographic distribution of HIV infection in Kenya.

The prevalence in HIV infection ranges from 2 percent to over 30 percent in 2001. This large range in estimates indicates that the epidemic is not distributed evenly throughout Kenya. In the southern half of the country, where most of the population resides and where most ANC surveillance takes place, the epidemic is clustered in areas with higher population density, along major transport routes, and near ports and borders. There is almost no data available for the more rural north.

2. India

a. What is the range (e.g., the highest and the lowest) in HIV prevalence among pregnant women reported by ANC sites in 2002? (Use the summary of urban and rural ANC surveillance date from 2002, shown on page 4 of the Fact Sheet, to answer this question.)

In 2002, the most recent year for which data is available, HIV/AIDS prevalence among pregnant women attending antenatal clinics (ANC) ranged from zero to 8.75 percent.

b. At what proportion of the sites where ANC women were tested in 2002 was HIV prevalence at least 1 percent? To answer this question you will need to use information on pregnant women at the 186 ANC surveillance sites shown in the Fact Sheet Annex on pages 18 to 25.

The proportion of sites where prevalence in 2002 was at least 1 percent is approximately 31 percent (57/186). There are 57 sites with HIV prevalence of at least 1 percent out of 186 sites listed in the Annex : Eluru, Etawah, Government Medical College at Auranga, Guntur, Hyderabad, Jind, Jodhpur, Kakinada, Karimnagar, Hubli KIMS, Kohima, Machillipatnam, Madurai, Mokoko Chung, Mysore, Nagpur, Nalgonda, Namakkal, Nasik, Nellore, Nizamabad, Ongole, Parbhani, Patna, Pune, Raichur, Raigarh, Imphal RIMS, Salem, Sangareddy, Sangli, Satara, Senapati, Aizwal, Amritsar, Anantapur, Bellary, Bijapur, Bilaspur, Champhai, Chittor, Churachandpur, Cuddapah, Devangere, Dimapur, Chandel District Hospital, Tamenglong, Tandur, Thane, Thoubai, Tirunelveli, Tuensang, Udipi, Ukhrui, Vellore, Vizianagaram, and Calcutta SG Hospital.

c. Describe the geographic distribution of HIV cases throughout the country using the map on page 5 of the fact sheet.

Although overall adult HIV prevalence is 0.8 percent, prevalence is highly variable throughout India. As you can see from the map on page 5, prevalence is in general higher in the south and southwest, and lower in the northern half of the country.

d. In order to understand trends in HIV prevalence, it is important to have repeated measurements from a surveillance site over time. Using the Fact Sheet Annex beginning on page 18, determine the number of clinics with data for at least three points in time that have experienced a consistent rise in prevalence (clinics that have had at least one increase and no decrease in prevalence in three consecutive observations). If there is surveillance data from a clinic for more than three years, use the three most recent years for this exercise.

There are 24 sites that have experienced a consistent rise in prevalence during their three most recent observations. These are Mandsaur District Hospital, Ratlam District Hospital, Raxaul Duncan Hospital, Shillong G.D. Hospital, Karnal Government Hospital, Madurai Medical College, Gorakhpur Mahila Hospital, Aizwal MCH Clinic, Salem Medical College, Daman PHC, Manipur State RIMS & M.C.W., Rothak District, Sangli, Christian Medical College & Hospital, Diu Civil Hospital, Silvassa Civil Hospital, Coimbat Coimbatore Medical College, Chindwara District Hospital, Umaid Hospital & Medical College J, Bangalore Vani Vials Hospital, Calcutta, J.J. Hospital & Government Medical, Mumbai 1 (Bombay), and Calcut School of Tropical Medicine.

e. What modes of HIV transmission are important in India? Use the assessment of the epidemiological situation on page 2 of the Fact Sheet to answer this question.

The epidemic in the south is driven mainly by heterosexual transmission, while in the north-eastern states of Manipur and Nagaland, transmission is due largely to injecting drug use. In urban southern states, over half of all sex workers are infected.

Exercise 2

1. Linking proximate determinants with biological determinants of HIV transmission

Proximate DeterminantExposure of susceptible to infected personsTransmission Efficiency:Duration of infectivity
SusceptibilityInfectiousness
Condom use   × ×  
Unsafe injections (reuse of needles, for example) ×      
Concurrency (having sexual partnerships that overlap) ×      
Coital frequency (how often a person has sex) ×      
Needle sharing ×      
Number of new sexual partners ×      
Circumcision   ×    
Abstinence ×      
STI (being infected with another sexually transmitted infection)   × ×  
Blood bank safety ×      
How needles and syringes are handled ×      
Age difference of sexual partners ×      
Age at first sex ×      
Older men partnering with younger girls for casual sex ×      
Injection drug user mixing patterns ×      

Explanation of the link between each proximate and biological determinant:

Proximate DeterminantRationale
Condom use

Lowers susceptibility if used for protection by a susceptible (uninfected) person, and lowers infectiousness by preventing transmission of virus from an infected person to a susceptible person

Unsafe injections (reuse of needles, for example)

Reusing needles makes it possible for a susceptible person to be exposed to blood from an infected person

Concurrency (having overlapping sexual partnerships)

Makes it more likely that a person will become infected with HIV from another partner and subsequently infect a regular partner

Coital frequency (how often a person has sex)

Can increase or decrease the amount of exposure of susceptible to infected persons; the more often a person has sex, the greater the opportunity for him or her to become infected or to infect someone else

Needle sharing

Can expose an uninfected person (susceptible) to the blood of an infected person

Number of new sexual partners

The greater the number of new sexual partners, the more opportunity for susceptible persons to be exposed to infected persons

Circumcision

Men who are circumcised are less likely to become infected with HIV

Abstinence

Prevents susceptible persons from coming into contact with persons infected with HIV

STI (being infected with another sexually transmitted infection)

It is postulated that open sores from STIs can increase an infected person's ability to pass on the HIV virus and can also increase a susceptible person's vulnerability to becoming infected

Blood bank safety

Where blood banks are free of HIV, there is no exposure of susceptible to infected persons; when blood banks are infected with HIV, blood transfusions provide an opportunity for susceptible persons to be exposed to HIV

How needles and syringes are handled

Safe needle handling practices lower the risk that susceptible medical personnel will be infected with HIV from an accidental needle stick that would expose them to an infected person's blood

Age difference of sexual partners

Younger people who are closer to their age of first sex have had less time to become infected than older sexually active people. When the age difference between partners is greater, it can mean that infected older people are more likely to come into contact with susceptible younger people

Age at first sex

A later age at first sex lowers the risk of exposure among younger people

Older men partnering with younger girls for casual sex

Young girls have had less chance to become infected than older men; when older men prefer to have sex with younger girls, there is a greater level of exposure of susceptible to infected persons

Injection drug user mixing patterns

When there is more mixing among needle-sharing partners, there is a greater chance that an infected person will enter into a partnership with a susceptible (uninfected) person.

2. Understanding the relationship between underlying, proximate, and biological determinants

Which biological determinant of HIV transmission is affected by new sexual partner acquisition? What are some underlying contextual determinants (socio-economic, socio-cultural, or demographic) of new partner acquisition? What kinds of intervention strategies could impact new sexual partner acquisition?

New sexual partnerships are a driving force behind the HIV epidemic because they lead to the exposure of susceptible (uninfected) people to infected people.

The underlying determinants of new partner acquisition are socio-economic as well as socio-cultural. Socio-economic factors affecting new partner acquisition include poverty which contributes to the prevalence of sex in exchange for money, and migrant labor which separates families and leads to increased contact between migrant laborers and sex workers. Socio-cultural factors include sexual norms and beliefs such as the mindset that a man can't be satisfied sexually by just one woman and the increased vulnerability of women to poverty in settings where women have low status.

Intervention strategies that could affect new sexual partner acquisition include educational campaigns that encourage people to remain faithful to one partner or to abstain, and campaigns to give girls small sums of money in order to deter them from exchanging sex for money or gifts. (These are only a selection of the possible answers!)

3. Visualizing relationships within the proximate determinant framework

PLACE Chart 3

4. PLACE seeks to reduce transmission efficiency among those most likely to be exposed to HIV. How do each of the following reflect this approach and how do each of the following fit into the Proximate Determinants framework?

a. PLACE locates public venues where people meet new sexual partners

Locating places where people meet new sexual partners allows policy-makers to identify areas where exposure of susceptible to infected persons is most likely to be taking place.

b. PLACE finds locations where injection drug users socialize

Locating places where injection drug users socialize allows policy makers to identify priority areas where interventions should be introduced to limit the exposure of susceptible to infected persons.

c. Treating STDs in members of mobile populations

Treating STDs in members of mobile populations is a way of targeting the efficiency of transmission per contact because co-infection with some STDs can make a person more likely to transmit or become infected with HIV. Because mobile populations are more likely to form new sexual or needle-sharing partnerships, targeting STD treatment to members of this group reduces transmission efficiency among those most likely to be exposed to HIV.

d. Providing condoms at places where sex workers solicit clients

Providing condoms at places where sex workers solicit clients is a way of reducing the efficiency of transmission among those most likely to transmit or to be exposed to HIV. PLACE can be used to identify these high transmission places.

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