Epidemics have in some cases been identified with the arrival of a new infection to a population with no prior exposure. The result is that a percentage of the population is unable to fully overcome the infection and it becomes chronic in them. This failure is usually due to a genetic characteristic.

In some cases, the infection is transmitted poorly which then allows the infection to 'burn-out' in a region.

1. 1934, Los Angeles City and California State, USA
2. 1936, Fond-du-Lac, Wisconsin, USA
3. 1937, Erstfeld, Switzerland
4. 1937, Frohburg Hospital, St. Gallen, Switzerland
5. 1939, Harefield Sanatorium, Middlesex, England
6. 1939, Degersheim, St. Gallen, Switzerland
7. 1945, University Hospital of Pennsylvania, USA
8. 1946-47, Iceland
9. 1948-49, North Coast Towns, Iceland
10. 1949-51, Adelaide, South Australia
11. 1950, St Joseph Infirmary, Louisville, Kentucky, USA
12. 1950, Upper New York State
13. 1952, Middlesex Hospital Nurses' Home, London, England
14. 1952, Copenhagen, Denmark
15. 1952, Lakeland, Florida, USA
16. 1953, Whitley Hospital, Coventry and Coventry District, England
17. 1953, Chestnut Lodge Hospital, Rockville, Maryland, USA
18. 1953, Jutland, Denmark
19. 1954, Tallahassee, Florida, USA
20. 1954, Seward, Alaska
21. 1954, British Army, Berlin, Germany
22. 1954, Liverpool, England
23. 1955, Dalston, Cumbria, England
24. 1955, Royal Free Hospital, London, England
25. 1955, Perth, Western Australia
26. 1955, Gilfach Goch, Wales (also some cases in Boscombe, Hants, England, East Ham, London) England
27. 1955, Addington Hospital, Durban and Durban City, South Africa ( Sporadic cases: Johannesburg, South Africa)
28. 1955-56, Segwema, Sierra Leone Oct 1955-Oct 1956
29. 1955-56, Patreksfordur and Thorshofn, Iceland
30. Oct 1955-April 1956, N.W. London, England,
31. 1956, Ridgefield, Connecticut, USA
32. 1956, Punta Gorda, Florida, USA
33. 1956, Newton-le-Willows, Lancashire, England
34. 1956, Pittsfield, Williamstown, Massachusetts, USA (Sporadic cases: Hygiea, Sweden )
35. 1956-57, Coventry, England
36. 1957, Brighton, South Australia
37. 1958, Athens, Greece, Switzerland (Sporadic cases: S.W. London, England)
38. 1959, Newcastle upon Tyne, England (Sporadic cases: N.W. London, England)
39. 1961-62, New York State
40. 1964-66, N. W. London, England
41. 1964-66, Franklin, Kentucky, USA
42. 1965-66, Galveston County, Texas, USA
43. 1967-70, Edinburgh, Scotland
44. 1968, Fraidek, Lebanon
45. 1969, Medical Centre, State University of New York, USA
46. 1970, Lackland Air Force Base, Texas, USA
47. 1970-71, Hospital for Sick Children, Great Ormond Street, London, England
48. 1975, Mercy San Juan Hospital, Sacramento, California, USA
49. 1976, Southwest Ireland
50. 1977, Dallas-Fort Worth, Texas, USA
51. 1979, Southampton, England
52. 1980-81, West Kilbridges, Ayrshire, Scotland
53. 1980-83, Helensburgh, Scotland, Stirlingshire, Scotland
54. 1982-84, West Otago, New Zealand, Dunedin and Hamilton, New Zealand
55. 1984 - 1992: "From 1984 until 1992 an endemic period occurred in which an unusually large number of clusters and epidemics of M.E./CFS have been recognized in North America. After an apparent initial increase in morbidity in 1983, there seemed to have appeared in late summer of 1984 an unprecedented increase of sporadic and epidemic cases across North America. Although certain geographical hot spots seem to have taken up much of the medical interest, this endemic situation probably represents an unusual and unremitting morbidity in all areas of the United States and Canada. Some of the clusters and epidemics are listed."
    • Incline Village, Lake Tahoe, Nevada, USA Epidemic August - September
    • Chapel Hill, North Caroline, USA
    • Montreal, Quebec-Ontario, Canada
56. 1984-85, Truckee, California, USA
57. 1985, Lyndonville Epidemic, New York, USA
    • SMON Epidemic in Japan
    • Zhi Fang Epidemic in China
    • "The status of these two epidemics in relation to M.E./CFS can only be speculation at this point.
58. 1985, Yerington, Nevada, USA
59. 1986, Placerville, California, USA
60. 1988, Sonora, California, USA
61. 1989, Roseville, California, USA
62. 1990, Elkgrove High School, Elkgrove, California, USA