Epidemiology of HIV

Background Information on Prevalence and Incidence
•   This session covers global and Tanzania -specific prevalence of HIV infection and reviews HIV mode of transmission.
•    In addition, this session discusses major factors influencing HIV transmission in Tanzania, population at risk, and the relationship between HIV and sexually transmitted infections.
• Prevalence: proportion or percentage of persons who are HIV-positive
o Calculated by dividing total number of HIV positive people in given place at given time by population:

i.e. Number of HIV positive X 100
Population. over
• Incidence: number of new patients with HIV in a given place over a given area
o Calculated within a specific time frame
o E.g. the number of new cases in 2005 = incidence for 200
•     Prevalence of HIV infection is affected by:
o Number of new cases of HIV (incidence) and
o Number who die or leave a given area

Global Burden of HIV
•   By December 2008, it is estimated that;
o Number of people living with HIV in 2008
Total 33.4 million Adults 31.3 million
Women 15.7 million
Children under 15 years 2.1 million
o People newly infected with HIV in 2008
Total 2.7 million
Adults 2.3 million
Children under 15 years 430 000
o AIDS-related deaths in 2008
Total 2.0 million
Adults 1.7 million
Children under 15 years 280 000

o Sub-Saharan Africa has only 10% of the world’s population but 68% of the world’s
HIV infections.
o By 2008, it was estimated that;
    Number of people living with HIV: 22.4 million
    Number of new HIV infections: 1.9 million
    Number of children newly infected: 390 000
    Number of AIDS-related deaths 2008: 1.4 million

HIV and AIDS in Tanzania
•   First 3 AIDS cases were identified in 1983
•   All 20 regions of the mainland had reported a case by the end of 1986
•   By December 2005:
o 205 773 AIDS cases had been reported since 1983
o 1 770 383 People Living with HIV (PLHIV)
o 440 000 PLHIV in need of Antiretroviral Therapy
•    By 2007, the National prevalence rate among adults is 5.7% (AIDS Epidemic updates by UNAIDS/WHO)

Modes of HIV Transmission
•   Unprotected sexual contact with an infected partner(s) including Men having sex with men (MSM).
•   In Africa, HIV is predominantly transmitted through heterosexual sex
•   Contact with HIV-infected blood/blood products.
•   Blood transfusion, injection drug use (IDU) through needle-sharing, needle stick
accidents, unsterilized needles.
•   Mother-to-Child transmission (In utero, during delivery and through breast feeding)
•   Risks of acquiring HIV infection differ depending on the mode of transmission 
•   Needle sharing, blood transfusion and anal intercourse carry the highest risk than other modes. In fact blood transfusion from an HIV positive donor carries the highest risk of HIV transmission i.e. 9,000 per 10,000 exposures.

Socio-Economic Factors
•   Poverty
o Children may leave home to work at earlier age
o Sex work
•   Loss of community cohesion
•   Migration caused by need for employment
o HIV/AIDS follows routes of commerce, i.e. truck routes
o Mines
•   Differences in economic opportunities and income for men and women
o In many places, women’s work pays less than for men

Social & Cultural Factors
•    Cultural factors
o Traditions, beliefs, and practices
o Polygamy
Wife inheritance ,Widow cleansing
o Female genital mutilation
o Culture can create barriers that prevent people, and especially women, from taking
precautions
o Tattooing
o Gender inequalities

In some cultures men are expected to have many sexual relationships
     Women suffer gender inequalities, often economic and social in nature
o Stigma and denial
Stigma prevents acceptance of the problem and early seeking of care
o Low awareness
   Lack of information necessary to understand and prevent HIV
False beliefs about effects of ART
•    Conflict and social unrest
o Civil unrest, especially armed conflict and displacement of people
o High-risk behaviour of military personnel
Behavioural Factors
•    Multiple sex partners
•    Concurrent sex partnership
Biological Factors
•   High rates of sexually transmitted infections
•   Lack of male circumcision
•   Women’s anatomy makes them more vulnerable
•   Transfusion of blood from an infected donor

Relationship Between HIV and STIs
•   STIs are a major risk factor for HIV transmission and acquisition
o Risk varies based upon type of STI e.g. ulcerative have higher risk of acquisition
while the non-ulcerative carry higher risk of transmission
•   STIs increase a person’s vulnerability to HIV in 2 main ways:

Ulcerative STIs cause open sores in genital area, allowing HIV to pass through open skin
o For all STIs, white blood cells gather at site of infection in order to fight infection and HIV targets these cells
•   HIV also increases vulnerability to STIs:
o HIV positive person co-infected with another STI may be more likely to transmit HIV
due to increase in HIV viral shedding
•   A suppressed immune response due to HIV can increase the:
o Reactivation of genital ulcers
o Rate of abnormal cell growth
o Difficulty in curing reactivated or newly acquired genital ulcers
o Risk of becoming infected with additional STIs
Examples of STIs
•    Ulcerative STIs:
o Syphilis: Common and frequently asymptomatic
o Herpes simplex virus type 2 (HSV-2)
o Other conditions:
Chancroid
Lymphogranuloma venereum (LGV)
Granuloma inguinale
•    Non-ulcerative STIs/discharge syndromes:
o Gonorrhea
o Chlamydia
o Trichomonas
o Other conditions:
Bacterial vaginosis
ƒ Candidiasis
HIV Transmission in Women
• Women are biologically more vulnerable to HIV than men because:
o Vaginal mucous membrane is more permeable than outside of penis
o Larger exposed surface area for women
o Ejaculate stays longer in female genital tract
o Complicated regulation of vaginal acidity: Lactobacilli are important in creating acidity in the vagina hence protecting infection from HIV and other pathogens
o Their population changes with age and when there is a decrease in the lactobacilli

population the woman becomes vulnerable to infections including HIV
o Lubrication that changes with age: dry vagina is vulnerable to trauma during sexual act and hence adding risk to HIV infection.

Posted by
Welfate Jambo