The two HIV-related SSD were u- or j-shaped with higher values for the very young and for older MSM.
The highest discrepancies between survey and surveillance data regarding HIV-prevalence were observed in the oldest age group in Sweden and the youngest age group in Portugal.
In 2010, the European MSM Internet Survey (EMIS) demonstrated the feasibility and utility of collecting data from MSM from 38 European countries with the same questionnaire – simultaneously available online in 25 languages – and using the same recruitment methods .
However, estimation and comparability of MSM HIV prevalence between countries (and between consecutive surveys) is limited by unknown sizes of MSM populations, differences in household internet access across countries and time , Marcus U, Hickson F, Weatherburn P, Schmidt AJ, et al.: Estimating the size of the MSM populations for 38 European countries by calculating the survey-surveillance discrepancies (SSD) between self-reported new HIV diagnoses from the European MSM Internet Survey (EMIS) and surveillance-reported HIV diagnoses among MSM in 2009 (as yet unpublished observations)], and possibly other unknown selection effects.
In cross-country comparisons household access to the internet was a major determinant of participation rates and survey surveillance discrepancies (SSD).Among the 38 countries with sample sizes larger than 100 respondents in EMIS we selected the following countries (in alphabetical order): the Czech Republic (Central East Europe); Germany (Central West Europe); the Netherlands (West Europe); Portugal (South West Europe); Sweden (North West Europe); the United Kingdom (West Europe).Countries were selected to represent a variety of European sub-regions and varying EMIS participation rates.Data on sexual risk behaviours among MSM are increasingly collected by online surveys .Data on recency of HIV testing and self-reported HIV diagnosis are also often collected in these surveys.
This study seeks to measure the differences in rates of age-specific survey participation, new HIV diagnoses, and HIV prevalence between MSM who participate in internet surveys and the general MSM population.