Migration is a phenomenon affecting all European countries, and having an influence on the health of the migrants as well as of populations of the host countries. Infectious diseases are still relevant in the context of migration. In addition, experiences during travel and in the host countries may negatively affect the health of migrants. Still, migrants largely suffer from similar health problems as the populations of the host countries. In consequence, today's discussion on migrant health is focusing more and more on equity and equality issues. For example, it is being investigated in many countries whether migrants have equal access to health care and social services. Observed health differentials serve as indicators for equity in access. A pertinent question in this context is whether migrants can access preventive services appropriately, and whether they benefit from preventive offers in the same way as the autochthonous population does. This question is understudied, as we show in this article, using the example of Germany.
There are different definitions of the term immigration. According to international definitions, immigration occurs when a person (in this paper always men and women unless otherwise stated) moves his or her centre of living over a socially meaningful distance, and it is international immigration when this occurs across national borders. In this paper, we only address international immigration.
As in several other countries, groups of immigrants in Germany are often defined solely on the basis of nationality and no difference is made between foreigners and immigrants. However, foreign citizenship does not always equate to an immigrant background. For example, there are people with foreign citizenship who were born in Germany and did not migrate themselves, and also immigrants with German citizenship, obtained e.g. through naturalization. In addition, there are people with an ethnic German background whose ancestors had settled in Eastern Europe. Many of these people have now returned to Germany, and are known as 'Spätaussiedler' or 'Aussiedler'.
Also noteworthy is the timing of migration. There can be meaningful differences between immigrants who have newly arrived in the host country, immigrants who have resided in there for years, and immigrants whose parents or grandparents immigrated many decades ago. Immigrant groups are heterogeneous; they include, for example, immigrant workers, their families, contract and seasonal workers, scientists, as well as immigrants with restricted residence permits. In addition, there are the group of refugees and asylum seekers from third world countries with their spouses and families.
Because of Germany's central European location, it has always been both a thoroughfare and an immigrant country. Two major immigration movements occurred since the 1950s, in addition to a large intake of refugees after the Second World War; (i) work migration and immigration of the families of the so called "guest workers", More than half of the 6,74 million people with foreign citizenship currently living in Germany originate from the Mediterranean, the largest portion, 25%, coming from Turkey , and (ii) the immigration of ethnic Germans known as Spätaussiedler. In total to date, approximately 4 million Spätaussiedler have migrated to Germany, principally from the former Soviet Union. Of these, about 2.5 million have come since the fall of the Iron Curtain .
In the 2005 partial census by the Federal Statistics Department (Mikrozensus), there were a total of 15.3 million people with an immigrant background, which corresponds to about 19% of the German population .
Germany has one of the largest immigrant populations in Europe. Due to the heterogeneity of origin and the wide range of reasons for immigration, it is not appropriate to make general statements about 'the' immigrants. Immigrants are a special group - made up of numerous subgroups - that differ to some degree from the majority population. Differences arise due to factors such as the primary reasons for migration, lifestyles (nutrition etc.), or discrimination because of the migrant origin. Immigrants are also more likely to have a below-average income, a lower education, as well as unfavourable working and living conditions . Concerning prevention, there are two core questions: which barriers do these immigrants face regarding access to preventive programs in a highly developed country like Germany and, what has (and could) be done to overcome these barriers?
The health of migrants is determined by a number of factors:
The conditions in the country of origin before migration (for example, different nutritional exposures, lower quality healthcare, violence, war, torture, and a higher prevalence of certain infectious diseases).
The conditions during the migration process (for example, psycho-social burdens and stress, hunger, violence, racism, separation from the family).
The conditions in the host country, both the immediate conditions after arriving (feeling 'foreign', separation from family, racism, language and comprehension problems) and the conditions that can have an influence years or generations later (different cultural and traditional ways of life, racism, lower educational status and social standing, continuing language problems).
In spite of these potentially adverse conditions, it should be noted that immigrants are often highly motivated and open-minded concerning changes, e.g. to adapt to a changed life situation. Through this, and often through to a significant social network, immigrants may have health opportunities alongside their health risks.
European health systems are only slowly adapting to the needs of migrants. For example, immigrant-specific offers in the health system of Germany were for a long time primarily related to infectious disease. During their migration, immigrants have an increased risk of suffering from an infectious disease, which must be taken into account by the health system. 'Exotic' infectious diseases at the population level, however, only constitute a small portion of the overall infectious disease burden and, in addition, are increasingly introduced by returning tourists. A more noteworthy challenge for health services are HIV-positive immigrants coming from high prevalence countries, mainly in sub-Saharan Africa . Other examples include chronic hepatitis infection among African immigrants , or tuberculosis, particularly among Spätaussiedler from the former Soviet Union . Infection control laws stipulate that Spätaussiedler and asylum seekers staying in the crowded conditions of refugee accommodation are screened for tuberculosis. However, the specific health situation of immigrants is not only evident in the realm of infectious disease risk, where specific programs for subgroups under risk are sensible. Many health problems of immigrants are similar to the general population, or caused by similar exposures, but the exposures are more or less common in specific immigrant groups resulting in higher or lower incidence or mortality of the immigrants.
For example, an analysis of cause of death statistics shows an overall lower mortality for persons of foreign nationality , immigrants with a Turkish background , and for the immigrant group of Aussiedler . This advantage levels out over time as mortality rates converge towards those of the German population. This lower mortality is also evident when analysing specific causes of death, such as most cancers and cardiovascular disease [11, 12]. Nevertheless, these conditions are the most frequent causes of death both in the autochthonous population and among migrants.
It has often been observed that immigrants have a mortality advantage over the autochthonous population. This phenomenon, known as the "Healthy Migrant Effect", is brought about by the prerequisite of general good health necessary for a prospective migrant labourer who applies for work. A low risk for certain diseases, such as for cardiovascular diseases in the Mediterranean region, may also contribute to this effect. Changes to the "old" risks brought along by the immigrants, and the development of new risks occurring with different lag times, lead to risks that differ from those of the majority population of the host country. For an overview of the current discussion on this topic, see Razum & Twardella 2002  or Spallek & Razum 2008 .
In spite of some health advantages, immigrant populations are considered a vulnerable group in terms of health. Immigrant needs should therefore be given proper attention in the field of health research, so that excess risks of specific immigrant groups can be identified and high-risk groups can be targeted. For example, children of immigrants have been found to have a significantly elevated prevalence of dental caries [15, 16], and an increased prevalence of obesity [17, 18], both in some kind preventable health conditions. Papers by Razum et al. 2008 , Zeeb & Razum 2006 , and Borde & David 2003  offer deeper insights into epidemiological investigations of immigrant health and healthcare in Germany.
In conclusion, immigrants are a heterogenic population with heterogenic health problems. Some immigrants have specific health problems, e.g. due to infectious diseases, but overall the most frequent health problems of most immigrants are similar to the autochthonous population. This is true especially for immigrants with long duration of stay or for descendants of immigrants.