**2. Background**

HIV infection remains a relevant issue in Europe in the field of public health. Moreover, scientific literature suggests an increasing HIV transmission in several European countries. MSM represent one of the most at risk populations for acquiring HIV. In 2009, 9,023 newly diagnosed HIV infections were reported among this population in Europe, which accounts for 35% of all HIV diagnoses in that year (European Centre for Disease Prevention and Control ECDC/World Health Organisation WHO – Regional Office for Europe, 2010; Likatavi ius et al., 2008). Moreover, in this specific population, a high level of risk behaviours associated with an increasing incidence of other Sexually Transmitted Infections (STI) clearly show the need for specific and targeted prevention campaigns (Dodds et al., 2005; Van de Laar et al., 2009).

Due to a lack of risk perception and also to perceived social stigma, MSM tend to refer a low level of VCT and active health seeking behaviours (MacKellar et al., 2005). In addition, social and cultural obstacles to testing can be perceived by MSM also in health facilities. From a methodological point of view, since the introduction of Highly Active Anti-Retroviral Therapy (HAART), AIDS has become less indicative of the underlying trends in HIV infection, for this population in particular. Data based on the clinical records, at the same time, seems to not realistically reflect the HIV trends for two reasons. On the one hand, clinical records often do not include information regarding hard-to-reach MSM, who are less likely to ask for VCT and regular testing. On the other hand, a low level of knowledge about the real serostatus is reported among MSM (Williamson & Hart, 2007; Mirandola et al., 2009). Therefore, specific surveillance and outreach research targeting MSM who cannot attend the clinical facilities, is strongly required in order to obtain a more realistic estimation of the HIV epidemic.

In this context, a need for reliable and comparable data across different countries is also a key issue in monitoring the spread of HIV and in providing meaningful prevention. Unfortunately, data are often collected across a number of countries or in the same country using different sampling methods, or different testing methods, or different testing algorithms. In addition, questionnaire items used in various studies are often based on different assumptions and they can vary greatly in terms of time frame of the questions (last 12 or 3 months, last intercourse), definition of risk sexual practice, etc. Finally, specific HIV surveys focusing on MSM are rarely repeated on a regular basis. For that reason, a lack of reliable data and trends on HIV epidemic is available for this at risk population.

In this framework, a specific Declaration of Commitment on HIV/AIDS and a Political Declaration on HIV/AIDS were proposed and adopted by the UN General Assembly in 2001. In these documents, a specific set of epidemiological and surveillance activities are suggested, as well as the adoption of the so-called UNGASS indicators. UNGASS indicators are a set of measures to be used among different countries in order to effectively monitor the HIV epidemic (Joint United Nations Programme on HIV/AIDS UNAIDS & World Health Organization WHO, 2009). The Declaration provides a comprehensive framework to achieve the Millennium Development Goal in order to reverse the HIV epidemic by 2015.

In addition, specific indications for developing and implementing a more effective surveillance system are provided in UNAIDS and WHO publications (UNAIDS & WHO, 2002, 2005). These documents suggest the adoption of the so-called Second Generation Surveillance System (SGSS), which foresees a set of detailed managerial and epidemiological procedures, as well as standardized processes and actions for managing surveillance studies . The SGSS foresees the implementation of surveys repeated on a regular basis according to different indicators, which require the collection of both behavioural and biological data. The SGSS provides a meaningful tool for developing prevention initiatives according to reliable data on HIV epidemics and behavioural patterns, which represent the major challenge for the coming years.

The "Capacity building in HIV/Syphilis prevalence estimation using non-invasive methods among MSM in Southern and Eastern Europe" – SIALON project was developed and implemented according to the main procedures and processes foreseen in the UNGASS declaration and in the SGSS approach. The SIALON project was funded in the framework of the 2003-2008 Public Health Programme (Work Plan 2007) and implemented by a team of European Public Institutions under the leadership of the Veneto Region in close collaboration with local partners ranging from Universities, teaching hospitals, epidemiological centres and Gay NGOs. In particular, the SIALON study was carried out in six cities of Southern and Eastern European countries: Barcelona (Spain), Bratislava (Slovakia), Bucharest (Romania), Ljubljana (Slovenia), Prague (Czech Republic), Verona (Italy).
