Background: Two in five people living with HIV in Europe were born outside of the European country where they were first diagnosed. However, there may be a misplaced belief that acquisition has predominantly occurred in the home country. To better inform prevention and testing programs, we provide country-specific estimates of the proportion of migrants who probably acquired HIV after arrival in their country of diagnosis (post-migration).
Methods: We analysed new HIV-diagnosis reports among migrants (defined by country of birth/origin) diagnosed in the United Kingdom (UK), Belgium, Sweden and Italy in 2011. We estimated a probable period of HIV seroconversion using modelled CD4-cell count distribution and decline speed shortly after seroconversion. A migrant was classified as having acquired HIV ''post-migration'' or ''abroad'', or ''overlapped'' when the estimated period of seroconversion was ''after'', ''before'' or ''overlapped with'' the year of arrival. At the population level, a lower estimate of the proportion of migrants having acquired HIV post-migration was gained when only those classified as ''post-migration'' were included; an upper estimate includes both those classified as ''post-migration'' and ''overlapped''; and a central estimate was gained when the ''overlapped'' were reassigned to either ''post-migration'' or ''abroad'' based on estimated median CD4-cell count and decline speed.
Results: 2,351 migrants were recruited (1,683 UK, 329 Belgium, 185 Sweden and 154 Italy). In all countries, the majority were aged 25-44 years (>70%), heterosexual (>70%) and born in Africa (>60%). Overall, an estimated 38% (range: 32-46%) of diagnosed migrants had probably acquired HIV post-migration. The UK had the highest proportion 43% (range: 36-52%) followed by Belgium 29% (26-34%), Sweden 24% (21-30%) and Italy 23% (20-27%). An estimated 42% (203/481; 38-50%) of men who have sex with men probably acquired HIV post-migration compared to 38% (658/1,713; 32-47%) among heterosexual people.
Conclusions: We present for the first time multi-country estimates of probable place of HIV-acquisition among migrants living with HIV in Europe. More than a third of migrants diagnosed in these four European countries acquired HIV post-migration, and this proportion was high in MSM and heterosexuals. Our findings call for targeted prevention efforts to reduce HIV transmission among the migrant populations within Europe.

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