Epidemiology 369SOCIODEMOGRAPHICS
Several studies have highlighted commonalities among indi-
viduals with CFS, including greater likelihood of being
female, Caucasian, and of higher socioeconomic status
(Reyes et al., 1997; Gunn, Connell, & Randall, 1993). How-
ever, community-based studies involving representative sam-
ples of ethnically and socioeconomically diverse populations
indicate that the prevalence of CFS is actually higher for
Latinos and African Americans than for Caucasians (Jason,
Richman, Rademaker, et al., 1999), and higher for individu-
als of lower socioeconomic status than for those of higher
socioeconomic status (Wessely, Chalder, Hirsch, Wallace, &
Wright, 1997). Ethnic group differences found in a commu-
nity sample of patients with CFS indicate that individuals
classi“ed as minorities experience signi“cantly more severe
symptomatology including sore throats, postexertional
malaise, headaches, and unrefreshing sleep than Caucasians,
and they additionally report poorer general health status
(Jason, Taylor, Kennedy, Jordan, et al., 2000). In addition,
Latinos who are female, older, and of higher SES report the
highest relative severity of fatigue (Song, Jason, & Taylor,
1999). Higher rates of CFS among low-income groups and
ethnic minorities may be attributed to psychosocial stress, be-
havioral risk factors, poor nutrition, inadequate health care,
more hazardous occupations, or environmental exposures
(Jason, Richman, et al., 1999).
CFS continues to be found to be more prevalent among
women than men (Jason, Richman, et al., 1999), and there is
some evidence of gender-related differences in the impact of
CFS as well as in its prevalence. Among a sample of individ-
uals with CFS, women were found to have a higher frequency
of “bromyalgia, tender/enlar ged lymph nodes, and lower
scores on physical functioning. Men had higher frequency of
pharyngeal in”ammation and a higher lifetime prevalence of
alcoholism (Buchwald, Pearlman, Kith, & Schmaling, 1994).
Jason, Taylor, Kennedy, Jordan, and associates (2000) found
that women with CFS had signi“cantly poorer physical func-
tioning, more bodily pain, poorer emotional role functioning,
signi“cantly more severe muscle pain, and signi“cantly more
impairment of work activities than men with CFS in a
community-based sample. Findings for increased symptom
severity and poorer functional outcomes among women may
involve certain predisposing vulnerabilities that may be more
likely to occur in women than in men. These could include
biological factors such as reproductive correlates (Harlow,
Signorello, Hall, Dailey, & Komaroff, 1998) and biopsy-
chosocial factors such as stress-associated immune modula-
tion (Glaser & Kiecolt-Glaser, 1998).
Some research has suggested that occupational circum-
stances may play a role in CFS. In particular, Jason and
associates (1998) have found estimates of prevalence of CFS
to be higher among a sample of nurses than in the general
population, indicating that nurses may be a high-risk group
for this illness. If CFS affects members of various profes-
sions at different rates or in different ways, this may reveal
new information regarding the etiology and characteristics of
the illness. In a recent epidemiologic study of CFS in a com-
munity sample (Jason, Taylor, Kennedy, Song, et al., 2000),
health care workers comprised over 15% of the group of
individuals with CFS, which is signi“cantly higher than the
composition of health care workers in the general U.S. popu-
lation. Similarly, Coulter (1988) found that 40% of the mem-
bers of a large U.S. patients• organization for individuals with
CFS were associated with the health care professions, and
Ramsay (1986) identi“ed an overrepresentation of doctors
among individuals with CFS.
Findings such as these suggest that certain occupational
stressors, such as exposure to viruses, stressful shift work that
is disruptive to circadian rhythms, and excessive work load
may compromise the immune system and put health care
workers at greater risk of infection or illness (Akerstedt,
Torsvall, & Gillberg, 1985; Jason & Wagner, 1998; Leese
et al., 1996). Hypothetical explanations highlighting the role
of disrupted circadian rhythms are, in part, supported by
biological “ndings among a sample of nurses working “ve
consecutive night shifts (Leese et al., 1996). Disruptions in
pituitary-adrenal responses to CRH found in that sample
were highly consistent with the neuroendocrine abnormali-
ties typically found in individuals with CFS (Leese et al.,
1996). However, these “ndings must be interpreted in light of
other studies that have not found an overrepresentation of
professionals among individuals with CFS (Euba, Chalder,
Deale, & Wessely, 1996).EPIDEMIOLOGYThe “rst widely publicized study of CFS epidemiology was
initiated by the CDC in the late 1980s (Gunn et al., 1993).
Investigators requested physicians in four cities to identify
patients with a speci“ed set of fatigue-related symptoms.
Prevalence rates of CFS were found to range from 4.0 to 8.7
individuals per 100,000 cases (Reyes et al., 1997). The major-
ity of CFS cases were White upper-middle-class women. This
epidemiological study conducted by the CDC, as well as others
(Lloyd et al., 1990), derived its sample from physician referrals
in hospital and community-based clinics. These studies, and