The theory of planned behavior (TPB) is a useful model for understanding social-cognitive determinants (i.e. attitude, perceived norms, and perceived behavioral control) of sexual risk reduction among adolescents. However, research using the TPB has emphasized main effects and has not considered the possibility of moderated associations. In addition to testing main effects, this study assessed the interactions between TPB constructs and investigated the influence of previous sexual experience when predicting adolescents’ intentions to use condoms and delay sexual activity. Results indicate that the TPB functions differently depending on previous sexual experience and type of risk reduction behavior. Perceived norms were the only consistent predictor of intentions for condom use and delay. Attitude moderated perceived behavioral control when predicting condom use intentions among sexually experienced youth. However, no other interaction effects were detected. Future directions for research and implications for practice are discussed.

Les hommes ayant des rapports sexuels avec des hommes (HSH) sont les plus touchés par le VIH. La prévention du VIH dans cette population doit aujourd'hui se diversifier grâce à divers outils visant à réduire le risque : traitement des personnes séropositives, traitement préventif chez les personnes séronégatives, et comportements de réduction des risques sexuels. Le dépistage du VIH est alors un enjeu crucial de la prévention.La diversification de l'offre de dépistage en France, notamment grâce au dépistage rapide et communautaire, est un résultat majeur de cette thèse. D'autres problématiques sont également investiguées : le recours au dépistage du VIH chez les HSH vivant au Cameroun et l'intérêt pour la recherche en prévention chez les HSH en France.Tous ces résultats sont confrontés les uns aux autres et sont mis en perspective, en termes de recherches à mener mais aussi en termes de recommandations pour les politiques de prévention à destination des HSH. / Men who have sex with men (MSM) are the most affected by HIV. In this population, HIV prevention must be diversified, using several tools aiming to reduce risks: treatment of HIV positive persons, preventive treatment among HIV negative persons and, sexual risk reduction behaviours. HIV testing thus becomes the cornerstone of HIV prevention.Diversifying HIV testing is one of the most important results of this thesis. Other questions are also addressed: access to HIV testing among MSM living in Cameroon and interest in prevention research among MSM in France.The discussion of all these results leads to several perspectives in terms of researches that should be conducted, but also in terms of recommendations for prevention policies towards MSM.

Mother-to-infant vertical transmission of HIV usually occurs during pregnancy, labor, delivery or breastfeeding. It is the third leading cause of transmission of HIV after sexual intercourse and blood transfusions. In 2008, 12 million women aged 15 years and above were anticipated to be living with HIV in countries within Sub-Saharan Africa. In this study, the association between parental HIV knowledge, attitudes and risk reduction practices, and HIV vertical transmission in Kenya were explored. The health belief model was used to help understand and interpret the findings. For this quantitative study, data were collected via surveys from 212 participants in 3 HIV clinics in Kenya. Data were analyzed using descriptive and inferential statistics. Around 45% of respondents lacked knowledge on key aspects of Prevention of Mother to Child Transmission (PMTCT) of HIV particularly on expressing and heat treating milk from HIV positive mothers to make it safe for their babies. About 65% of Participants had awareness towards Mother to Child Transmission (MTCT) of HIV. Logistic regression showed no association between socioeconomic factors and parental knowledge on MTCT of HIV. Logistic modeling found that there was association between attitude and MTCT, revealing that attitude increased the likelihood to influence MTCT. Being married was associated with reduced risk of MTCT of HIV. The overall results indicated gaps in knowledge and information packaging. The potential positive social change implication of this study is that factors related to HIV vertical transmission identified in this study might be utilized to develop and implement HIV prevention strategies to reduce HIV vertical transmission and decrease associated morbidity and mortality among this vulnerable population.