**5. Conclusions**

This study obtained new eye-witness accounts of the 1955 Royal Free outbreak of ME from ex-Royal Free hospital staff, medical students, and patients who had developed the disease. Clinical and epidemiological features described by them, are consistent with an outbreak of an infectious illness affecting the lymphatic, muscular, and nervous systems, with long-term neurological defects in a few cases. Their accounts did not describe the expected features of epidemic hysteria. McEvedy and Beard's hypothesis that epidemic hysteria was the cause of this outbreak was based solely on the examination of selected patient case notes. We show that data given by McEvedy and Beard to support their

epidemic hysteria hypothesis are flawed. Specifically, some data was contradicted by the study group's first-hand accounts of the outbreak. Some data did not distinguish between epidemic hysteria and ME. Some data preferentially supported an organic etiology, and some data was of doubtful validity. This study confirms that ME/CFS is an organic disease and repudiates the hypothesis of it being a psychosomatic illness.

**Author Contributions:** Conceptualization, R.U. and R.B.; Data curation, R.U.; Formal analysis, R.U.; Investigation, R.U. and R.B.; Methodology, R.U. and R.B.; Project administration, R.B.; Writing— Original draft, R.U.; Writing—Review & editing, R.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research did not receive any specific gran<sup>t</sup> from funding agencies in the public, commercial, or not-for-profit sectors.

**Institutional Review Board Statement:** Not applicable as no experiments were done on humans or animals.

**Informed Consent Statement:** Not Applicable as all participants volunteered to provide recalled information on the outbreak

**Data Availability Statement:** Enough data is given in the paper to show exactly how the was done. There is no further data.

**Acknowledgments:** The authors thank the ex-staff of the Royal Free Hospital who experienced the 1955 outbreak of ME and who participated in this survey. The authors also thank Alan Gurwitt, MD, Yale Child Study Center and University of Connecticut School of Medicine, Harvard Medical School (retired) for reviewing psychiatric data in this paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
