Mathematical modelling based on the Dutch HIV epidemic suggests
that, in that country at least, heterosexual immigrants from Africa and the
Caribbean stand more risk of acquiring HIV in the Netherlands than they do in
their home country.
This is because when migrants enter host countries, their
sexual networks tend to be concentrated amongst people of their own background
and there is very little mixing with the host country population.
Maria Xiridou of the Netherlands National Institute of
Public Health and the Environment told delegates that surveillance had already
found that immigrants in Europe tended to have higher HIV prevalence than people in their home country. Was this a
characteristic of the type of person who moved abroad, or was it due to risks
encountered once they had moved?
Xiridou devised a mathematical model that used immigration
and HIV surveillance to calculate the proportion of immigrants who arrived already HIV-positive, the proportion who became infected on trips back home,
and the proportion who acquired it in the Netherlands.
HIV incidence among heterosexuals in the Netherlands in 2010
was estimated at 1 infection in 47,000 people a year, but was 1 in every
1170 Africans and 1 in every 4600 Caribbeans. Because incidence is higher in
immigrants, 72% of heterosexuals acquiring HIV in the Netherlands are migrants.
Interestingly, infections seemed to be concentrated even
more amongst partners of migrants, with 81% of partners of migrants who
acquire HIV being migrants themselves. This is because, in the Netherlands at
least, sexual mixing between the native and immigrant populations is rare. Eighty
per cent of heterosexual contacts reported by African men were with African
women and 77% of encounters among
people from the Caribbean were with others from the Caribbean. Dutch native men reported that a mere
0.3% of sexual contact was with an African or Caribbean woman.
She found that 29.7% of HIV infections recorded in the
Netherlands among the three groups in her model (African, Caribbean and
native Dutch) were due to infections acquired abroad, the vast majority of them
acquired before ever entering the country, with 78% of those infections being
The remaining 70.3% of infections were acquired in the
Netherlands. But because ethnic mixing was rare, native Dutch people represented
only 21% of infections acquired in the Netherlands while Africans represented
32% of them and people from the Caribbean 18%. Because of their smaller population, therefore,
immigrant groups were very considerably more vulnerable to acquiring HIV in the
Netherlands than were Dutch natives.
Because of this, changes in immigration policy would have
large effect on HIV incidence in the immigrant population, but virtually no
effect on infections in native Dutch people. A purely theoretical ban on HIV-positive immigrants would cut new HIV infections in already-arrived immigrants
by 30%. A more humane ‘test and immediately treat’ policy for new immigrants
would be more effective; the HIV incidence rate amongst the total immigrant
population would fall from 65 cases a year in 100,000 people to only 10 cases.
Xiridou commented that her model reinforced anecdotal
evidence that the proportion of HIV infections amongst immigrants that were acquired
in the host country were increasing, and emphasised that the HIV ‘threat’ from
immigration was largely confined to immigrants themselves.