Abstract
The prevalence of CFS (Chronic Fatigue Syndrome) and chronic fatigue were investigated in family members of CFS patients using a questionnaire-based study. Significant differences were seen between the prevalence of CFS in all groups of family members relative to the published community prevalence of 0.422% (spouses/partners: 3.2%, p < 0.001; offspring: 5.1%, p < .001; parents and siblings: 1.1%, p < 0.02; second and third degree blood relatives 0.8%, p < 0.02). The prevalence of CFS was higher in genetically unrelated household contacts and in nonresident genetic relatives than in the community, indicating that both household contact and genetic relationship are risk factors for CFS.