FACTOR-ANALYSIS OF UNEXPLAINED SEVERE FATIGUE AND INTERRELATED SYMPTOMS - OVERLAP WITH CRITERIA FOR CHRONIC-FATIGUE-SYNDROME

The objective of this study was to identify factors explaining the cor relations among unexplained severe fatigue of different durations (1-5 months or greater than or equal to 6 months) and symptoms reported as being significant health problems during a preceding 4-week period. B etween June and December of 1994, a cross-sectional, random digit dial ing telephone survey was conducted among residents of San Francisco, C alifornia. All subjects who reported having severe fatigue lasting for greater than or equal to 1 month and a random sample of nonfatigued s ubjects were asked to participate in a detailed telephone interview. D ata from 1,510 individuals aged 18-60 years who did not have medical o r psychiatric conditions that could explain their severe fatigue were analyzed. Common factor analyses identified three correlated factors ( defined as ''fatigue-mood-cognition'' symptoms, ''flu-type'' symptoms, and ''visual impairment'') that explained the correlations among fati gue lasting for greater than or equal to 6 months and 14 interrelated symptoms. No factor explained the correlations among fatigue lasting f or 1-5 months and other symptoms. The combination of fatigue of greate r than or equal to 6 months' duration and selected symptoms overlaps w ith published criteria used to define cases of chronic fatigue syndrom e (CFS). Although symptoms described in this study were reported as ap pearing within the preceding month, and CFS symptoms must have been pr esent for the previous 6 months, these results provide empirical suppo rt for the interrelations among unexplained fatigue of greater than or equal to 6 months' duration and symptoms included in the CFS case def inition.