[Methods of infectious disease epidemiology for public health services: case control studies as bridge between practical work, surveillance and epidemiology].

Routine surveillance of infectious diseases is one important task of national public health services. Due to globalization the impact of international disease monitoring rises. The volume of traffic and trade is constantly increasing, which makes a spread of infectious diseases to distant places more likely then ever. This are challenges international infectious disease networks have to deal with. Thus, the role of investigation of disease outbreaks is not only relevant for local level; it furthermore prevents broader spread. To eliminate outbreak sources good epidemiological analyses have to be conducted. However, this often leads to extra time and personal resources. In addition classical studies, like case-control studies, underlay methodical limitations. Case-control studies, especially if conducted on the basis of notified cases from surveillance data, are susceptible to bias (like selection- and recall bias). Another study design, the case-case study (case-case comparison), provides an alternative, which is less affected by such limitations. In this approach a number of cases related within an outbreak, is compared with a group of infected individuals of the same disease, not belonging to the outbreak. Results from recently published studies lead to the assumption that this study design is adequate for the investigation of infectious disease outbreaks, captured by surveillance systems. The practical application of this study design makes it especially useful for local public health services and thus provides a bridge between surveillance, epidemiology and practical work in Public Health.