Objectives: This paper aims to estimate the percentage of European men who  have sex with men (MSM) who may benefit from pre-exposure prophylaxis  (PrEP), applying the three most widely used HIV risk indices for MSM  (MSM Risk Index, Menza score, San Diego Early Test (SDET) score) and  drawing on a large-scale multisite bio-behavioural survey (Sialon II).

Methods: The Sialon II study was a bio-behavioural survey among MSM  implemented in 13 European cities using either time-location sampling or  respondent-driven sampling. Biological and behavioural data from 4901  MSM were collected. Only behavioural data of HIV-negative individuals  were considered. Three widely used risk indices to assess HIV  acquisition risk among MSM were used to estimate individual HIV risk  scores and PrEP eligibility criteria.

Results: 4219 HIV-negative MSM were considered. Regardless the HIV risk  score used and the city, percentages of MSM eligible for PrEP were found  to range between 5.19% and 73.84%. Overall, the MSM Risk Index and the  Menza score yielded broadly similar percentages, whereas the SDET Index  provided estimates constantly lower across all cities. Although all the  three scores correlated positively (r>0.6), their concordance was  highly variable (0.01<CCC<0.62).

Conclusion: Our findings showed the impact of different scoring systems on the  estimation of the percentage of MSM who may benefit from PrEP in  European cities. Although our primary aim was not to compare the  performance of different HIV risk scores, data show that a considerable  percentage of MSM in each city should be offered PrEP in order to reduce  HIV infections. As PrEP is highly effective at preventing HIV among  MSM, our findings provide useful, practical guidance for stakeholders in  implementing PrEP at city level to tackle HIV infections in Europe.

Keywords: HIV; pre-exposure prophylaxis; preventive health services; public health; sexual behaviour.