Study recruitment base and participants
. Participants were recruited based on a mailed questionnaire study regarding fatigue  and abdominal complaints  to all individuals with outbreak related laboratory confirmed giardiasis . Five years after the outbreak, patients who reported chronic fatigue in this questionnaire were invited to participate in a thorough clinical evaluation and screening. Fifty three individuals agreed to participate. Five patients were excluded from this study after evaluation. Two control groups were recruited; 22 individuals with normal score (=11) in the questionnaire three years after, and 10 healthy individuals not affected by the outbreak (unexposed controls) and without particular abdominal symptoms or fatigue.