An international collaborative group of experienced investigators met (in 2000, 2001, and 2002) for a series of 3-day workshops to identify and discuss problems in application of the 1994 CFS case definition. This paper that resulted from the deliberations represents a synthesis of evolving knowledge in the field.

CFS is defined by symptoms and disability, has no diagnostic physical signs or laboratory abnormalities, and its causes and pathology remain unknown. So, diagnosis is based on self-reported symptoms and ruling out treatable medical and psychiatric causes, and treatment is aimed at relieving symptoms rather than a cure.

Research has been constrained by ambiguities in the case definition. When this happens it is difficult to compare different findings because different subgroups of patients have been studied. In essence, one investigator is studying apples, the next oranges.

In this paper, an international group came together to reach an agreement on exactly what the case definition means, agree on exclusion criteria, and agree to use comparable measures to define CFS.

Since this paper came out, nearly every study of CFS has relied on the criteria it describes. Investigators can now compare apples to apples. Moreover, many of the recommendations are useful for health care providers (and their patients) because they specify standardized measures of the symptoms and disability associated with CFS.

CFS is a U.S. Department of Health and Human Services priority and the Centers for Disease Control and Prevention (CDC) is responsible for public health research to control the illness. The CDC has been involved in CFS research since the illness was first recognized as a public health problem and has been the international leader in developing diagnostic criteria. The primary obstacle has been lack of medical and public acceptance of CFS as a valid illness.

Every illness has societal and political implications. Between one and four million Americans suffer CFS, half have been ill for at least seven years, a quarter of those with the illness are unemployed or receiving disability, and the average affected family forgoes approximately $20,000 in annual earnings and wages. Yet, fewer than 20% of those afflicted have received medical care for CFS.

Despite more than 3,000 articles in the peer-reviewed medical literature, the pathophysiology of CFS is not well understood. There are no diagnostic laboratory abnormalities or clinical tests. There is no public health control or prevention strategy for CFS. This paper helps to resolve some of the research obstacles related to classification, provides investigators and clinicians tools with which to evaluate the clinical course and response to treatment, gives peer reviewers clearer guidelines, and removes some of the obstacles for funding.