The balance of positive and negative effects of specific messages in the evaluation of interventions for preventing HIV infection

The study objectives were to determine the effects of a large-scale school- based HIV prevention campaign, in terms of both positive and negative effec ts of each single message, and to identify sub-populations more at risk. Fo rty-six schools, randomly sampled from all schools in the Lazio region, wer e randomized to either an intervention or a control group. The study popula tion consisted of 3866 students. Questionnaires on AIDS-related knowledge a nd risk perceptions were administered to students before and after the inte rvention. Odds ratios were calculated to represent the extent to which the intervention was associated with an improvement (OR +), and the extent to w hich it prevented a worsening (OR -). Overall, the intervention was success ful in communicating important messages, such as the impossibility of trans mitting HIV through social contacts (OR + all significantly > 1 and OR- alw ays < 1), the meaning of seropositivity (OR+: 1.28, 95% CI: 0.99-1.64; OR-: 0.73, 95% CI: 0.58-0.91), and the lack of a resolutive cure for AIDS (OR : 1.61, 95% CI: 1.10-2.36; OR-: 0.76, 95% CI: 0.57-1.02). The worst result s were observed in vocational and art schools, where OR + > 1 were observed for only three questions and OR - values usually exceeded 1. This study hi ghlights the necessity of remodelling the intervention, indicating which me ssages need to be modified. The low impact of educational programmes among students of vocational and art schools makes them a population more at risk , that should be considered as a priority target population for interventio ns.