Analysis of two large household surveys in KwaZulu-Natal, South Africa, are casting some light on the dynamics of HIV transmission in the South African province that is hardest hit by the HIV / AIDS. Adolescents and young women contract HIV from older men, with wide margin in these age groups, while older women often contract HIV from their age group. Men and women who migrate only fifty km from home are more likely to become positive than those who remain in their community.
The two recently published studies, each using data from large household surveys in two different areas of KwaZulu-Natal. Migrations and relationships of disparate ages have been identified as factors that lead to HIV epidemic in southern Africa, but these analyzes were sophisticated in detail in order to clarify and reinforce the evidence of how these factors act.
Age intervals between sexual partners - study
The first study, by Tulio de Oliveira, Ayesha Kharsany and colleagues, is published online ahead of print inHIV Lancet.The data come from a random sample for HIV testing.
The researchers used phylogenetic analysis to identify the transmission links - in other words, groups of individuals who carried strains of HIV samples genetically similar and probably contracted HIV each other.Phylogenetic analysis showed estimates were as closely related to samples of viral strain of HIV in different individuals are compared with samples of HIV.
Of note, individuals who were with good adherence to treatment and had a low viral load were not included in the phylogenetic analysis due to the fact that the technique is not yet completely reliable, away from the study subjects with viral loads below 1000 copies / ml . In fact, this has the advantage of excluding the study people under treatment who are not would be likely to transmit HIV - the sample for phylogenetic analysis is skewed to people with recent infections, many of them undiagnosed.
A total of 9812 individuals participated in the study, of which 3969 were seropositive for HIV. Of these, 1589 had a viral load over 1000 copies / ml and provided blood samples that were successfully sequenced for phylogenetic analysis.
Four hundred and sixty-nine of these samples were grouped in 202 transmission groups, of which ninety subgroups included at least one woman and one man. These groups were then analyzed ninety with an even greater depth.
Age intervals between sexual partners - the main conclusions
Ninety groupings were possible 188 pairings between men and women. A comparison of all possible pairs on age and sex categories identified two particular patterns.
First, twenty percent of pairings were men between the ages 25 40 years and females aged 15-25. Second, thirty-one percent pairings were men and women who were both aged 25-40.
In other words, men aged 25-40 are the main source of HIV _contração_ in adolescents and young women.
Many of these men probably contracted the HIV infection of women aged 25 40 the years, the group with the highest HIV prevalence.
Over time, when the current group of teenage girls and young women reach their thirties, they will become the next group of women with high HIV prevalence and are likely to perpetuate HIV transmission cycle for men in their thirties - that will infect the next cohort of adolescent girls and young women. (See newspaper article graph illustrating the transmission cycle).
Age differences between men and women in transmission groups were large for younger women, but not older women. Women aged 15-20 had male partners, an average of 11,5 years older; women aged 21-25 7,0 had years older partners; women aged 26-30 1,5 had years older partners; women aged 31-35 1,7 had years older partners.
Of men aged 25-40, which were linked to a younger woman, 40% were also associated with a woman in her own age group.
People that were broadcast groups were often unaware of their infection, not taking treatment and had a high viral load.
internal migration - study
Labour migration is another key issue behind the HIV epidemic in South Africa, having a major impact on sexual partnerships between men and women. The second study, by Adrian Tuck, Frank Tanser and colleagues is published in the January issue ofAIDS.Data from a longitudinal cohort of all households in a predominantly rural area, within the Umkhanyakude district of KwaZulu-Natal.
The community is characterized by frequent migration to other parts of South Africa, marital low rates, multiple sexual partners and high rates desoropositividade positive for HIV that have not been diagnosed.
All households were visited annually (between 2004 and 2014) and researchers interviewed and tested for HIV every member of the household over the age of 15 years, who agreed to participate. Migration Information, which was carefully recorded were everywhere, watching when and where people migrated and that region paraqual region. When household members were absent, the researchers asked the relatives and friends about their whereabouts.
The analysis focuses on 17.743 individuals who were tested for HIV twice or more as part of the study and can therefore analyze the relationship between HIV infections and migration.
internal migration - the main conclusions
Within the analyzed cohort, about one in five men and women around their twenties migrated at least once and usually for periods between 8 and 24 months. A quarter of all migrations were the places within a range of 100 km and the main destinations of these migrations were:
- Richards Bay (the 55km away)
- Durban (205km) and
- Johannesburg / Pretoria (473km).
Migration to nearby destinations were associated with an increased risk, especially for men:
- Men who migrated from 40km in one year had one 50% increased risk of acquiring HIV (hazard ratio 1,5).
- Men who migrated around 169km in one year had a 75% higher risk.
- Men who went from 44% of their time away from the community of origin would run a 50% higher risk of contracting HIV.
Risk for women was associated with the more migration and more time than men:
- Women who migrated 109km in one year had a 50% higher risk of contracting HIV.
- Women who migrated 652km had a 75% higher risk.
- Women who spent more than 90% of their time away from the community at home had a 50% higher risk.
"Average migratory distances per year and increased periods of residence outside the community represent in rural studies for the main risk factors for acquiring HIV, such as increasing the number of sexual partners, increased likelihood of sexual behavior risk, family estrangement, friends, community, and social norms, increased vulnerability, or lower socioeconomic status, "the authors say.
In 21 International AIDS Conference (AIDS 2016) in Durban this yearFrank Tanser - one of the authors of the study - said that phylogenetic analyzes in this district also highlighted the importance of migration. A number of new infections throughout the local area can be linked back to individuals living in 'hot spot' communities alongside the highway.
Especially as migrants are often diagnosed late and have difficulty engaging with and Retension on health care, the researchers say HIV testing and treatment services in South Africa need to be better tailored to the needs of migrants.
Originally published in 14 2016 in DecemberMigration and age differences between male and female partners fueling the HIV epidemic in South Africa
Translated, revised, edited by Claudio Souzaon December 17 2016.