2004 Bergen, Norway outbreak
In 2004, in Bergen, Svartediket, Norway, an outbreak of chronic fatigue syndrome followed a contamination of the water supply with the parasite, Giardia.
Of the 1252 people sickened by Giardia, 253 scored high enough on the Chalder fatigue scale to be invited in a follow-up study five years later by Haukeland University Hospital and University of Bergen, Norway. Of those invited, 53 participated. The study concluded that 41.5% of the participants had chronic fatigue syndrome and 13.2% had Idiopathic Chronic Fatigue according to the Fukuda criteria.
The patient cohort continues to be studied by the University of Bergen and Haukeland University Hospital.