Evidence is mounting that a group of AIDS-like retroviruses are to blame for chronic fatigue, a debilitating condition marked by loss of energy and other ailments, such as depression, memory or concentration impairment, muscle and joint pain and shortness of breath. As this link becomes more definitive, employers should prepare for a wave of new chronic fatigue diagnoses, and for a big jump in disability costs.

Studies show that as many as 1 million Americans (most working-age adults) have chronic fatigue, though only about one in five has been diagnosed. With no obvious cause for what has been defined as a "syndrome," doctors often don't diagnose it, attributing the symptoms to psychological issues.

The Social Security Administration, the courts and private disability insurers have granted disability claims in cases where there has been a chronic fatigue diagnosis, but attorneys specializing in disability cases say that the lack of a cause discouraged such claims, and made it easier for disability insurers to invoke the "subjective claim limitation" clause in disability policies, which generally limits employee disability payments to two years when no underlying cause can be found.