| 1. |
- Hansson, Disa
(författare)
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Hidden desires : Modelling sexual behaviour and the spread of sexually transmitted infections
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we use statistical and mathematical models to study different sexual behaviours of relevance for the spread of sexually transmitted infections (STIs). Two groups of special interest for STI interventions are considered: sexually active youths and men who have sex with men (MSM). The focus of the first paper is on mechanisms giving rise to the observed condom use and anal sex behaviour among young people in Sweden. We study the sexual dispositions of individuals, how these interact and generate the observed sexual outcome. The second paper concerns the sexual behaviour of MSM in Sweden and the transmission process of HIV within this population. The population is modelled by a stochastic dynamic network which incorporates both steady partnerships and casual contacts. We model the spread of an infection where individuals are susceptible, infectious, or diagnosed (and unable to transmit) and derive the basic reproduction number R0, the probability of a major outbreak and the endemic prevalence.
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| 2. |
- Hansson, Disa, et al.
(författare)
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Introducing pre-exposure prophylaxis to prevent HIV acquisition among men who have sex with men in Sweden : insights from a mathematical pair-formation model
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Objectives Since 2017, the Public health Agency of Sweden recommend that pre-exposure prophylaxis for HIV (PrEP) should be offered to high-risk individuals, in particular to men who have sex with men (MSM). The objective of this study is to develop a mathematical model investigating the effect of introducing PrEP to MSM in Sweden.Design A pair-formation model, including steady and casual sex partners, is developed to study the impact of introducing PrEP. Two groups are included in the model: sexually high-active MSM and sexually low-active MSM. Three mixing assumptions between the groups are considered.Setting A gay-friendly MSM HIV/STI-testing clinic in Stockholm, Sweden. This clinic started offering PrEP to MSM in October 2018.Participants The model is calibrated according to detailed sexual behaviour data gathered in 2015 among 403 MSM.Results By targeting sexually high-active MSM, a PrEP coverage of 3.5% of the MSM population (10% of all high-actives) would result in the long-term prevalence to drop considerably (close to 0%). While targeting only low-actives would require a PrEP coverage of 35% for a similar reduction. The main effect of PrEP is the reduced susceptibility, whereas the increased HIV-testing rate (every 3rd month) among PrEP users plays a lesser role.Conclusions To create a multifaceted picture of the effects of interventions against HIV, we need models that include the different stages of HIV infection and real-world data on detailed sexual behaviour to calibrate the mathematical models. Our findings conclude that targeting HIV high-risk individuals, within HIV risk populations such as MSM, with PrEP programmes could greatly decrease the long-term HIV prevalence in Sweden. Therefore, risk stratification of individuals is of importance in PrEP implementation programmes, to ensure optimising the effect and cost-effectiveness of such programmes.
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| 3. |
- Hansson, Disa, 1986-
(författare)
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Modelling Sexual Interactions : Sexual behaviour and the spread of sexually transmitted infections on dynamic networks
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we develop statistical and mathematical models to study different factors of relevance for the spread of sexually transmitted infections (STIs). Two special interest groups for STI interventions are considered: sexually active youths and men who have sex with men (MSM). The statistical models developed make it possible to estimate individuals’ dispositions towards sexual behaviours related to the spread of STIs: condom use and anal sex. To study the spread of an infection in a population we use mathematical models. The mathematical models in this thesis give insights into the transmission process of HIV among MSM in Sweden—a population at high risk for HIV infection.The focus of the first paper is on mechanisms giving rise to observed sexual behaviour, such as condom use, among sexually active youths in Sweden. We study the sexual dispositions of individuals and how these interact and generate the observed sexual outcomes.The second paper concerns the sexual behaviour of MSM in Sweden and the transmission process of HIV within this population. The population is modelled by a stochastic dynamic network model that incorporates both steady partnerships and casual contacts. We model the spread of an infection where individuals are susceptible, infectious or diagnosed (unable to transmit) and derive the basic reproduction number R0, the probability of a major outbreak, and the endemic prevalence.The third paper further develops the dynamic network model of the second paper. The model now takes into account that individuals may be sexually high-active or sexually low-active. The division into two activity groups makes it possible to study a preventive intervention against HIV that is only targeted to sexually high-active. The intervention studied is pre-exposure prophylaxis for HIV (PrEP), i.e. that the antiviral drugs tenofovir-emtricitabine are taken by individuals with negative HIV serostatus to prevent getting infected by HIV. We study the PrEP coverage needed to reduce the observed HIV prevalence of 5% to a value close to 0%.In the fourth and final paper we focus on condom dispositions among MSM. The disposition models from the first paper are extended to better fit an MSM population and are additionally extended to be used for more types of sexual behaviour data.
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