It is common knowledge that both respiratory tract infections (RTI) and gastrointestinal infections (GTI) cause a large part of short periods of days off from work, day care and school. In addition, because of the generally mild nature of the diseases, especially adults often come to work in spite of symptoms, and may therefore initiate transmission of infection among their colleagues. The chain of events from exposure to a pathogenic virus to subsequent infection and staying home because of infectious disease is a very complicated one, and is affected by many factors potentially causing variation, such as the multitude of causative agents, different individual histories of infections, variability of inter-personal contacts in work and various working- team feelings -influenced thresholds for staying home etc. Therefore, we aim to recruit at least 24 operationally distinct volunteer groups, each including at least 50 persons, and to continue the intervention about 18 months.