Background: The study of partners can help to understand the impact of environmental influences on the development of allergies. We aimed to test the hypothesis that subjects whose partners have hay fever are at increased risk for the same disease and that the risk increases with the time subjects live together with an affected partner.
Methods: A nested unmatched case-control study was performed in a random sample of 4261 inhabitants, aged 25-74 years, of the City of Augsburg, Germany, and two adjacent counties. Using standardized computer-assisted face-to-face interviews, we determined the risk of doctor-diagnosed hay fever in subjects who lived together with a partner having the same disease as opposed to subjects living with an unaffected partner. Furthermore, the risk of doctor-diagnosed hay fever depending on the time the subjects had lived together with an affected partner was calculated.
Results: After adjustment for age, sex, parental predisposition and social status, the risk of hay fever was more than double in subjects who lived together with a partner having the same disease (odds ratio, OR(adj.), 2.41; 95% confidence interval, CI, 1.48-3.92). If subjects lived together with an affected partner, the risk of developing the disease increased with the time the partners lived together (1-11 years, OR 1; 12-23 years, OR 1.8; 24-35 years, OR 7.4; 36-54 years, OR 13.7).
Conclusion: The risk of developing hay fever is significantly elevated in subjects who live together with a partner having the same disease. The risk further increases with the time the partners live together. This points to important shared environmental influences or behaviours and raises speculations on a transmissible cause.