Chapter 1
Key Concepts in Epidemiology Of HIV in Pakistan
Learning Objectives:
The learner should be able to
- Name Key Populations (KPs) or High-Risk Groups (HRGs) for HIV
- Recognize 'vulnerable' groups and 'bridging' populations
- Identify modes of transmission in Pakistan
- List attributable risk of acquiring HIV per high-risk exposure
- Discuss the context of 'outbreaks' in Pakistan
- Identify the lack of knowledge on 'high' prevalence districts
HIV can affect anyone regardless of sexual orientation, race, ethnicity, gender, age or where they live. However certain groups in Pakistan are more likely to get HIV infection than others due to increased exposure to risk factors.
What is 'general population' in Pakistan?
People with standard/low risk of acquiring HIV because of no high-risk behaviors. This group usually has an HIV prevalence of less than 0.1%.
What is a generalized epidemic?
Epidemics are termed “generalized" if transmission is sustained by sexual behaviour in the general population (typically defined on the basis of population prevalence of >1%). Eg. Southern and parts of eastern Africa have 'generalized' epidemics.
What is a 'Key Population'/'High-Risk Group' in Pakistan?
Key Populations (KP) are defined groups in the population who due to specific higher-risk behaviors, are at higher risk of acquiring HIV infection irrespective of the epidemic type or local context. KPs generally have a high prevalence of HIV and have high potential for transmission of infection due to repeated high-risk behaviors. They may also have legal and social issues which contribute to risk of getting infected through poor access to preventive and therapeutic resources.
Examples of KP/HRGs in Pakistan include Intravenous Drug users (due to contaminated needle-sharing), male and female and transgender sex workers (repeated unprotected sexual exposure) and Men who have Sex with Men (repeated unprotected sexual exposure). Both terms are used interchangeably.
What is a concentrated epidemic?
Epidemics are termed 'concentrated' if transmission largely occurs in clearly defined high risk groups such as men who have sex with men (MSM), people who inject drugs (PWIDs) and sex workers (SWs) eg. The epidemic in Pakistan is categorized as a 'concentrated epidemic' in Key Populations (meaning: prevalence in KPs >1%).
What is a 'vulnerable' population in Pakistan?
People in the population whose living conditions are prone to factors which place them at risk of contracting HIV but not 'as high' as 'Key Populations'. Examples in Pakistan include long-distance drivers, displaced populations, deportees, immigrants, adolescents or orphans on the street (street children), women and children with repeated exposure to unsafe injection apparatuses/blood transfusion in high prevalence districts.
What is a 'bridging' population in Pakistan?
People who may or may not belong to Key Populations but have the potential to act as a 'bridge' for introducing HIV infection into the general population. Classically this group was composed of spouses, partners, clients or those who network with KPs (overlapping high-risk behaviors). Example: a bisexual MSM who has had sex or shared needle with an IDU may act as 'bridge' for transmission of HIV to his spouse and children or male sexual partner, a Pakistani deportee from Middle East who has had sexual exposure to a female or male sex worker may act as 'bridge' for transmission to his wife and children, street youth with exposure to IDU or sexual abuse may act as 'bridge' when sharing needle with non-street youth.
Bridging in the context of horizontal transmission (unsafe injections) is not well understood in Pakistan.
Modes of HIV Transmission in Pakistan
Multi-modal Transmission of HIV holds true for Pakistan too like the rest of the world.
Adult men, adult women and transgender individuals can acquire the infection by the following routes
Multi-modal Transmission of HIV holds true for Pakistan too like the rest of the world.
Adult men, adult women and transgender individuals can acquire the infection by the following routes:
1. Sexual transmission
- Unprotected sex with an infected individual
2. Horizontal Transmission
- Unsafe Blood Transfusion from an infected individual
- Minor or major surgical procedures with unsterilized instruments
- Repeated needle-sharing with an infected individual
3. Vertical Transmission
- Born to an infected mother who was undiagnosed and/or untreated during pregnancy or puerperium
Children (0 to less than 18 years) can acquire the infection by the following routes:
1. Horizontal Transmission
Unsafe Blood Transfusion from an infected adult
Repeated exposure to contaminated injection and infusion apparatus used for medications and intravenous fluids as part of medical treatment
2. Vertical Transmission
- In-utero or peripartum transmission from infected mother who was undiagnosed and/or untreated during pregnancy
- Breastfeeding by an infected mother who is undiagnosed and/or untreated and/or on treatment but not virally suppressed
3. Sexual Transmission
- Unprotected sex (± abuse) with an infected adult remains a largely theoretic but nevertheless important risk factor to explore in positive children
Each exposure above has an attributable risk of HIV acquisition per episode. Repeated episodes multiply risk of acquisition.
Prevalence in General Population
Pakistan has an estimated population of 231 million, one of the highest population growth rates (1.7% annual growth since 2020) and one of the highest fertility Rates (3.4 children per woman) in South Asia. No population-based HIV prevalence survey has been done however estimated prevalence in general population in Pakistan is 0.2%.
Concentrated Epidemic in Key Populations
Pakistan has a concentrated epidemic in its Key Populations (prevalence >1% in KPs).
According to Pakistan's fifth Integrated Biological and Behavioral Surveillance Round (2016-2017), HIV prevalence is rising steadily among key populations, including PWIDs (38.4%), transgender sex workers (7.5%), transgender individuals (7.1%), male sex workers (5.6%), men who have sex with men (5.4%), and female sex workers (2.2%). (10) Sex workers (especially female) are experiencing the fastest increase in prevalence.
Despite these alarming trends, treatment coverage remains critically low at 12.5% of estimated KPs, and prevention program coverage varies significantly, from a mere 3% for non-sex worker men who have sex with men to 27-29% for PWIDs, underscoring the insufficient impact on controlling the epidemic.(11)
Fifty-three percent of total estimated 270000 PLHIV are from key populations: 25 % among Men who have sex with men (MSM), 24% People who inject drugs (PWIDs), 2% female sex workers (FSWs), 2% transgender (TGs).
The HIV epidemic in Pakistan follows the Asian Epidemic Model (AEM) pattern, where initial stabilization among people who inject drugs (PWIDs) is now overshadowed by rising transmission through sexual networks and bridging groups into the general population. (7)
Where are 'new infections' happening in Pakistan?
In 2019, 77% of new infections occurred through male-to-male sex (45%), needle sharing among PWID (26%), and sex work (6%). A further 19% of new infections were likely transmitted from married MSM, PWID, and clients of sex workers to their female spouses. This means that, according to the model, currently 90% of transmissions are coming from key populations and sex worker clients and, the majority of these transmissions are occurring in the context of male-to-male sex and needle-sharing for drug use.
Programmatic coverage of Key Populations, however, remains abysmally poor.
Given this coverage, and without any new effort to achieve key population programme scale-up, the model below projects the distribution of new infections to increase as follows:
This modeling exercise has shown that the proportion of new infections accounted for by MSM increases significantly. This is why the low coverage of this population is of great concern. As the 'new' epidemic driver in Pakistan, meaningful research to increase understanding of this population, its dynamics, its barriers to access, and how to tailor interventions to its needs is of national priority.
Attempts to gauge incidence and prevalence among KPs have been made through modeling exercises. Prevalence among all KPs in Pakistan is projected to increase from 16% in 2015 to 25% in 2025.
Similarly, HIV incidence among all KPs combined was projected to increase rising from 15 in 2015 to 18 per 1000 person-years by 2025. The increase is attributed to rising incidence among H/MSWs and FSWs.
Rising Incidents of Bridging and Outbreaks in General Population
Of the total estimated number of PLHHIV in Pakistan, 47% PLHIV belong to either 'bridging' populations (non-key populations with close proximity to key populations- spouse/sexual partner/needle-sharer belonging to KP) or belonging to 'general' population (no known risk factor identified).
The past decade has shown an increase in parenteral outbreaks of HIV in districts with a high prevalence of HIV in Key Populations.
The most devastating example of bridging into the general population was the 2019 Larkana Outbreak where a large number of children tested positive (only 9% had positive mothers). Women and children are now considered a 'vulnerable' group in Pakistan especially in districts where the epidemic among Key populations is not in control and bridging populations exist. This is because of the 'higher than standard' risk of HIV acquisition associated with their health-seeking behavior (exposure to contaminated needles, blood transfusions, surgical procedures including childbirth with unsterilized instruments) especially if they reside in districts with high HIV prevalence among Key Populations. There is no data on population-based prevalence among the general population in Pakistan.
References
HIV infection predominantly affecting children in Sindh, Pakistan, 2019: a cross-sectional study of an outbreak. The Lancet Infectious Diseases. 2020 Mar 1;20(3):362-70.
Risk of HIV Transmission from Blood Transfusion. Confronting AIDS: Directions for Public Health, Health Care, and Research. Committee on a National Strategy for AIDS, Institute of Medicine, National Academy of Sciences. ISBN: 0-309-55495-0, 374 pages, 6 x 9, (1986)
Summary of Presentations on related topic from: Training Workshops for HIV National and Provincial Program Physicians (WHO/UNICEF) (Mir, Mahmood)
Integrated Biological & Behavioral Surveillance In Pakistan 2016-17 2017 [cited 2024 15 july]. Available from: https://nacp.gov.pk/repository/whatwedo/surveillance/Final%20IBBS%20Report%20Round%205.pdf.
Pakistan AIDS Strategy IV 2021-2025 2020 [cited 2024 18 july]. Available from: https://hivpreventioncoalition.unaids.org/sites/default/files/attachments/aids_strategy_pakistan_iv_2021-2025.pdf.pdf
UNAIDS. Pakistan Country factsheet 2022 [Available from: https://www.unaids.org/en/regionscountries/countries/pakistan. aidsdatahub. SNAPSHOT 2023 PAKISTAN 2023
[Available from: https://www.aidsdatahub.org/sites/default/files/resource/pak-snapshot-2023.pdf.
WHO. HIV in the WHO Eastern Mediterranean Region 2016 [UNAIDS. Data Pakistan 2023 [Available from: https://www.aidsdatahub.org/sites/default/files/resource/pakistan-data-book-2023.pdf.
UNAIDS. Country progress report - Pakistan 2019 [cited 2024 18 july]. Available from: https://www.unaids.org/sites/default/files/country/documents/PAK_2019_countryreport.pdf..
Melesse DY, Shafer LA, Emmanuel F, Reza T, Achakzai BK, Furqan S, Blanchard JF. Heterogeneity in geographical trends of HIV epidemics among key populations in Pakistan: a mathematical modeling study of survey data. J Glob Health. 2018 Jun;8(1):010412.
