Spatial distribution and registry-based case-control analysis of Campylobacter infections in Denmark, 1991-2001

Using data from an 11-year period (1991-2001), the authors analyzed available information on location of residence for all registered, laboratory-confirmed, domestically acquired cases of campylobacteriosis in Denmark. Patient data were merged with data from a national register on housing and addresses, and a population density index was constructed using the Danish population register. The study was performed as a register-based case-control study; 15 age-matched controls for each case were selected from the national population register. A total of 22,066 cases were compared with 318,958 controls in logistic regression analysis. Living in types of housing found in rural areas and living in areas with a low population density were both associated with an increased risk of infection. This relation concerned children in particular and explained one third of cases among children in the countryside. Furthermore, in some counties there was an association between infection and type of drinking-water company serving the home. This study indicated that contact with animals or the environment is the source of a substantial proportion of sporadic Campylobacter infections in the Danish countryside, particularly among children.