Background
Methods
Study design
Data collection
Statistical analyses
Results
Demographic characteristics
Characteristics | Exclusionary Condition | Odds ratio (OR)* | ||||||
---|---|---|---|---|---|---|---|---|
All | Yes | No | Unadjusted Ors | Adjusted Ors | ||||
n
= 781
|
n
= 280 (36%)
|
n
= 501 (64%)
|
(95% CI)
†
|
(95% CI)
| ||||
Part A
Classification | ||||||||
CFS-like | 291 | (37.26) | 141 | (48.45) | 150 | (51.55) |
3.25 (2.03-4.80)
| 1.50 (0.79-2.87) |
Unwell | 267 | (34.19) | 89 | (34.19) | 178 | (66.67) |
1.73 (1.15-2.59)
| 0.89 (0.53-1.52) |
Well | 223 | (28.55) | 50 | (22.42) | 173 | (77.58) | 1.00 | 1.00 |
Age (years), mean (SD) | 43.50 | (10.36) | 43.10 | (10.39) | 43.73 | (10.35) | 0.94 (0.81-1.09) | 0.83 (0.70-1.00) |
Sex | ||||||||
Male | 186 | (23.82) | 71 | (38.17) | 115 | (61.83) | 1.14 (0.81-1.60) | 1.44 (0.96-2.16) |
Female | 595 | (76.18) | 209 | (35.13) | 386 | (64.87) | 1.00 | 1.00 |
Race | ||||||||
Black | 195 | (24.97) | 91 | (46.67) | 104 | (53.33) |
1.86 (1.34-2.60)
|
1.89 (1.24-2.88)
|
Other | 35 | (4.48) | 13 | (37.14) | 22 | (62.86) | 1.26 (0.62-2.56) | 1.12 (0.51-2.45) |
White | 551 | (70.55) | 176 | (31.94) | 375 | (68.06) | 1.00 | 1.00 |
Residential areas | ||||||||
Rural | 383 | (49.04) | 144 | (37.60) | 239 | (62.40) |
1.81 (1.16-2.82)
|
2.02 (1.20-3.39)
|
Urban | 266 | (34.06) | 103 | (38.72) | 163 | (61.18) |
1.90 (1.19-3.02)
|
1.96 (1.16-3.29)
|
Metropolitan | 132 | (16.90) | 33 | (25.00) | 99 | (75.00) | 1.00 | 1.00 |
BMI (kg/m2), mean (SD) | 28.08 | (5.34) | 28.76 | (5.52) | 27.70 | (5.20) |
1.22 (1.05-1.41)
| 1.02 (0.86-1.22) |
Part B
MFI | Per SD increment | Per SD increment | ||||||
General fatigue | 12.90 | (4.69) | 14.10 | (4.36) | 12.22 | (4.74) |
1.52 (1.30-1.78)
| 1.23 (0.87-1.74) |
Physical fatigue | 10.86 | (4.37) | 12.05 | (4.32) | 10.20 | (4.25) |
1.54 (1.32-1.79)
| 1.06 (0.78-1.44) |
Reduced activity | 9.24 | (4.16) | 10.13 | (4.33) | 8.75 | (3.98) |
1.39 (1.20-1.61)
| 0.93 (0.72-1.19) |
Reduced motivation | 9.58 | (3.90) | 10.60 | (4.12) | 9.01 | (3.66) |
1.51 (1.30-1.76)
| 1.21 (0.92-1.59) |
Mental fatigue | 10.94 | (4.54) | 12.09 | (4.50) | 10.29 | (4.43) |
1.50 (1.29-1.74)
| 1.12 (0.89-1.40) |
SF-36 | Per SD increment | Per SD increment | ||||||
Physical Functioning | 75.64 | (24.03) | 67.57 | (26.41) | 80.11 | (21.35) |
1.68 (1.44-1.95)
| 0.62 (0.34-1.10) |
Role physical | 41.41 | (41.60) | 27.14 | (37.45) | 49.50 | (41.68) |
1.78 (1.52-2.09)
| 0.70 (0.50-0.99) |
Bodily pain | 60.61 | (26.63) | 52.35 | (26.93) | 65.23 | (25.34) |
1.65 (1.41-1.92)
| 0.66 (0.41-1.07) |
Social functioning | 71.32 | (27.78) | 62.28 | (29.17) | 76.37 | (25.65) |
1.67 (1.43-1.94)
| 1.08 (0.70-1.68) |
Mental health | 68.50 | (22.23) | 62.29 | (23.05) | 71.98 | (20.99) |
1.55 (1.33-1.80)
| 1.11 (0.63-1.94) |
Role emotional | 49.12 | (43.31) | 37.74 | (41.49) | 55.49 | (43.05) |
1.52 (1.31-1.77)
| 1.08 (0.78-1.50) |
Vitality | 47.77 | (28.01) | 41.39 | (27.03) | 51.38 | (27.94) |
1.44 (1.24-1.67)
|
1.61 (1.02-2.53)
|
General health | 61.87 | (23.57) | 55.24 | (23.88) | 65.58 | (22.58) |
1.56 (1.34-1.82)
| 0.98 (0.64-1.52) |
PCS | 46.28 | (10.72) | 43.07 | (11.64) | 48.08 | (9.72) |
1.60 (1.38-1.86)
| 1.50 (0.40-5.68) |
MCS | 44.67 | (12.79) | 41.27 | (13.63) | 46.58 | (11.89) |
1.52 (1.31-1.76)
| 0.68 (0.22-2.07) |
HUI2† | 76.14 | (14.61) | 70.75 | (14.80) | 79.16 | (13.61) |
1.82 (1.56-2.13)
| Not included§
|
SI | Per SD increment | Per SD increment | ||||||
SI_CFS | 23.13 | (20.58) | 28.13 | (21.45) | 20.34 | (19.56) |
1.45 (1.25-1.68)
| 0.78 (0.56-1.08) |
SI_NCFS | 19.89 | (18.09) | 24.44 | (20.21) | 17.34 | (16.26) |
1.48 (1.27-1.71)
| 1.04 (0.79-1.37) |
Exclusionary conditions
Telephone interview | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
All | Excluded (n= 1609)* | |||||||||||
Medical (only) | Psychiatric (only) | Medical and psychiatric | Missing data | Subtotal (%) | ||||||||
n
| (%) |
n
| (%) |
n
| (%) |
n
| (%) | |||||
CFS-like | 910 | 48% | 350 | 79.4 | 60 | 13.6 | 31 | 7.0 | 0 | 0 | 441 | 27.4 |
Unwell | 2635 | 37% | 827 | 84.2 | 105 | 10.7 | 50 | 5.1 | 0 | 0 | 982 | 61.0 |
Well | 2085 | 9% | 164 | 88.2 | 16 | 8.6 | 6 | 3.2 | 0 | 0 | 186 | 11.6 |
Total | 5630 | 29% | 1341 | 83.3 | 181 | 11.3 | 87 | 5.4 | 0 | 0 | 1609 | 100 |
Clinic evaluation | ||||||||||||
CFS-like | 291 | 49% | 57 | 40.1 | 62 | 43.7 | 22 | 15.5 | 1 | 0.7 | 142 | 50.4 |
Unwell | 267 | 43% | 56 | 49.6 | 46 | 40.7 | 11 | 9.7 | 1 | 0.9 | 114 | 40.5 |
Well | 223 | 12% | 20 | 76.9 | 6 | 23.1 | 0 | 0.0 | 0 | 0.0 | 26 | 9.2 |
Total | 783 | 36% | 133 | 47.2 | 114 | 40.4 | 33 | 11.7 | 2 | 0.7 | 282 | 100 |
Telephone interview (n= 5558*) | Clinic evaluation (n= 781*) | |||
---|---|---|---|---|
n
| (%) |
n
| (%) | |
Medical
| ||||
Morbid obesity (BMI> = 40 kg/m2) | 335 | 6.0 | 0 | 0 |
Pregnancy within the past year | 282 | 5.1 | 0 | 0 |
HIV or AIDS | 33 | 0.6 | 0 | 0 |
Organ transplantation | 14 | 0.3 | 0 | 0 |
Sleep disorders | 289 | 5.2 | 1 | 0.1 |
Neurological |
†105 | 1.9 | 4 | 0.5 |
Autoimmune/inflammatory |
‡88 | 1.6 | 33 | 4.2 |
Cardiovascular | 77 | 1.4 | 12 | 1.5 |
Infection |
§46 | 0.8 | 1 | 0.1 |
Cancer | 28 | 0.5 | 0 | 0 |
Diabetes mellitus Type 1 | 22 | 0.4 | 22 | 2.8 |
Blood disorders | 23 | 0.4 | 32 | 4.1 |
Lung disease | 19 | 0.3 | 6 | 0.8 |
Liver | 16 | 0.3 | 1 | 0.1 |
Renal | 11 | 0.2 | 3 | 0.4 |
Surgery | 10 | 0.2 | 0 | 0 |
Thyroid/pituitary | 5 | 0.1 | 42 | 5.4 |
Other | 72 | 1.3 | 9 | 1.2 |
Psychiatric
| ||||
Bipolar | 72 | 1.3 | 36 | 4.6 |
Substance abuse | 49 | 0.9 | 63 | 8.1 |
Schizophrenia | 30 | 0.5 | 16 | 2.0 |
MDD/M | NE | 41 | 5.2 | |
Anorexia/bulimia | 7 | 0.1 | 11 | 1.4 |
Other | 7 | 0.1 | 0 | 0 |
CFS (n = 213) | ISF (n = 421) | NF (n = 147) | |||
---|---|---|---|---|---|
Medical conditions | |||||
Thyroid | 23.81% | Thyroid | 26.76% | Anaemia | 25.00% |
Diabetes | 19.05% | Anaemia | 18.31% | Thyroid | 25.00% |
Anaemia | 9.52% | Diabetes | 16.90% | Autoimmune | 15.00% |
Heart | 9.52% | Autoimmune | 14.08% | Diabetes | 10.00% |
Inflammatory | 9.52% | Inflammatory | 4.23% | Heart | 5.00% |
Arthritis | 7.14% | Heart | 2.82% | Hematologic | 5.00% |
Autoimmune | 7.14% | Kidney disease | 2.82% | Inflammatory | 5.00% |
Pulmonary | 7.14% | Metabolic | 2.82% | Kidney disease | 5.00% |
Kidney disease | 2.38% | Stroke | 2.82% | Metabolic | 5.00% |
Metabolic | 2.38% | Arthritis | 1.41% | Arthritis | 0.00% |
Sleep | 2.38% | Brain tumour | 1.41% | Brain tumour | 0.00% |
Brain tumour | 0.00% | Dehydration | 1.41% | Dehydration | 0.00% |
Dehydration | 0.00% | Pain syndrome | 1.41% | Liver disease | 0.00% |
Hematologic | 0.00% | Pulmonary | 0.00% | Pain syndrome | 0.00% |
Pain syndrome | 0.00% | Haematologic | 0.00% | Pulmonary | 0.00% |
Stroke | 0.00% | Liver disease | 0.00% | Sleep | 0.00% |
----------- | ------------------ | Sleep | 0.00% | Stroke | 0.00% |
Psychiatric conditions | |||||
MDD/M | 47.73% | Substance abuse | 57.35% | Psychosis | 50.00% |
Bipolar | 27.27% | Bipolar | 26.47% | Substance abuse | 50.00% |
Substance abuse | 22.73% | MDDM | 14.71% | MDDM | 0.00% |
Psychosis | 11.36% | Anorexia | 10.29% | Bipolar | 0.00% |
Anorexia | 2.27% | Psychosis | 7.35% | Anorexia | 0.00% |
Characteristics of clinic population with medical versus psychiatric exclusions
Type of exclusion | |||||||
---|---|---|---|---|---|---|---|
Med (n= 133) | Psych (n= 114) | Both (n= 33) |
p-value | ||||
n
|
%
|
n
|
%
|
n
|
%
| ||
Sex
| 0.0143 | ||||||
Female | 109 | 81.95 | 75 | 65.79 | 25 | 75.76 | |
Male | 24 | 18.05 | 39 | 34.21 | 8 | 24.25 | |
Race
| 0.6690 | ||||||
Black | 48 | 46.09 | 33 | 28.95 | 10 | 30.30 | |
White | 78 | 58.65 | 77 | 67.54 | 21 | 63.64 | |
Other | 7 | 5.26 | 4 | 3.51 | 2 | 6.06 | |
Residential areas
| 0.3099 | ||||||
Rural | 60 | 45.11 | 65 | 57.02 | 19 | 57.58 | |
Urban | 57 | 42.86 | 35 | 30.70 | 11 | 33.33 | |
Metropolitan | 16 | 12.03 | 14 | 12.28 | 3 | 9.09 | |
Mean | SD | Mean | SD | Mean | SD | ||
Duration of fatigue (months) *
†
| 105.45 | 96.73 | 59.92 | 59.58 | 120.17 | 92.96 | 0.0003 |
BMI
| 29.27 | 5.68 | 27.94 | 5.38 | 29.55 | 5.10 | 0.115 |
MFI
| |||||||
General fatigue †‡ | 13.10 | 4.55 | 14.69 | 4.18 | 16.15 | 2.99 | <0.001 |
Physical fatigue *‡ | 11.68 | 4.49 | 11.74 | 4.09 | 14.58 | 3.68 | 0.002 |
Reduced activity ‡ | 9.54 | 4.19 | 10.11 | 4.41 | 12.55 | 3.88 | 0.002 |
Reduced motivation ‡ | 9.95 | 3.86 | 10.71 | 4.33 | 12.88 | 3.57 | 0.001 |
Mental fatigue†‡ | 10.83 | 4.39 | 13.05 | 4.32 | 13.85 | 4.24 | <0.001 |
SF-36
| |||||||
Physical functioning* | 67.86 | 27.04 | 71.36 | 24.82 | 53.33 | 25.15 | 0.002 |
Role physical ‡ | 31.20 | 40.17 | 27.41 | 36.28 | 9.85 | 23.33 | 0.013 |
Bodily pain | 54.08 | 26.85 | 53.23 | 26.29 | 42.18 | 28.05 | 0.067 |
Social functioning ‡ | 68.80 | 26.72 | 58.44 | 30.87 | 49.24 | 26.51 | <0.001 |
Mental health†‡ | 71.43 | 18.78 | 56.18 | 24.07 | 46.55 | 19.84 | <0.001 |
Role emotional†‡ | 48.87 | 43.53 | 31.58 | 39.13 | 14.13 | 23.61 | <0.001 |
Vitality*†‡ | 48.83 | 26.81 | 38.03 | 26.50 | 23.03 | 17.59 | <0.001 |
General health*‡ | 57.67 | 24.09 | 56.48 | 22.33 | 41.18 | 24.19 | 0.001 |
PCS* §
| 42.22 | 11.64 | 45.43 | 11.32 | 38.31 | 11.16 | 0.0040 |
MCS†‡§
| 46.55 | 11.24 | 37.36 | 14.72 | 33.47 | 10.02 | <0.0001 |
HUI2*‡§
| 74.50 | 14.32 | 69.34 | 14.72 | 60.50 | 11.25 | <0.0001 |
Symptom scores
| |||||||
CFS symptom summary score ‡ | 23.98 | 20.70 | 30.13 | 21.14 | 37.98 | 21.90 | 0.0014 |
Non-CFS symptom summary score†‡ | 18.71 | 17.93 | 27.86 | 30.38 | 35.67 | 21.40 | <0.0001 |
Risk factors for an exclusionary diagnosis in subjects otherwise CFS
Characteristics | Exclusionary condition | Odds ratio (OR) | ||||||
---|---|---|---|---|---|---|---|---|
All | Yes | No | Unadjusted ORs | Adjusted ORs | ||||
n
= 210
|
n
= 100 (48%)
|
n
= 110 (52%)
|
(95% CI)
†
|
(95% CI)
| ||||
Telephone Classification | ||||||||
CFS-like | 169 | 80.48 | 85 | 50.30 | 84 | 49.70 | 1.75 (0.87-3.54) | 1.48 (0.61-3.56) |
Unwell | 41 | 19.52 | 15 | 36.59 | 26 | 63.41 | 1.00 | 1.00 |
Age (years), mean (standard deviation, SD) | 45.06 | (9.65) | 45.99 | (8.98) | 44.22 | (10.19) | 1.21 (0.92-1.59) | 1.06 (0.74-1.54) |
Sex | ||||||||
Male | 38 | 18.10 | 18 | 47.37 | 20 | 52.63 | 0.99 (0.49-2.00) | 1.65 (0.69-3.92) |
Female | 172 | 81.90 | 82 | 47.67 | 90 | 52.33 | 1.00 | 1.00 |
Race | ||||||||
Black | 35 | 16.67 | 14 | 40.00 | 21 | 60.00 | 0.67 (0.32-1.40) | 0.56 (0.20-1.52) |
Other | 13 | 6.19 | 5 | 38.46 | 8 | 61.54 | 0.63 (0.20-1.99) | 0.62 (0.15-2.51) |
White | 162 | 77.14 | 81 | 50.00 | 81 | 50.00 | 1.00 | 1.00 |
Residential areas | ||||||||
Rural | 106 | 50.48 | 54 | 50.94 | 52 | 49.06 | 2.28 (0.99-5.29) | 1.47 (0.51-4.20) |
Urban | 72 | 34.29 | 36 | 50.00 | 36 | 50.00 | 2.20 (0.91-5.30) | 1.53 (0.55-4.27) |
Metropolitan | 32 | 15.24 | 10 | 31.25 | 22 | 68.75 | 1.00 | 1.00 |
Body mass index (kg/m2), mean (SD) | 28.69 | (5.18) | 29.50 | (5.42) | 27.95 | (4.87) |
1.36 (1.03-1.79)
|
1.47 (1.05-2.06)
|
Multidimensional fatigue inventory | Per SD increment | Per SD increment | ||||||
General fatigue | 17.05 | (2.36) | 17.34 | (2.09) | 16.79 | (2.57) | 1.27 (0.96-1.70) | 1.22 (0.81-1.84) |
Physical fatigue | 14.52 | (3.31) | 14.88 | (3.22) | 14.19 | (3.38) | 1.24 (0.94-1.63) | 0.83 (0.52-1.34) |
Reduced Activity | 11.96 | (4.10) | 12.33 | (4.19) | 11.63 | (4.02) | 1.19 (0.90-1.56) | 0.83 (0.54-1.26) |
Reduced Motivation | 12.44 | (3.38) | 13.05 | (3.63) | 11.89 | (3.05) |
1.43 (1.07-1.89)
| 1.44 (0.94-2.20) |
Mental fatigue | 14.05 | (3.75) | 14.49 | (3.72) | 13.65 | (3.75) | 1.25 (0.95-1.65) | 1.19 (0.80-1.77) |
SF-36 | Per SD increment | Per SD increment | ||||||
Physical functioning | 57.37 | (24.54) | 52.83 | (24.01) | 61.45 | (24.40) |
0.70 (0.53-0.92)
| 0.77 (0.28-2.12) |
Role physical | 9.05 | (19.45) | 5.50 | (13.09) | 12.27 | (23.40) |
0.67 (0.48-0.93)
| 0.63 (0.40-1.00) |
Bodily pain | 38.30 | (19.86) | 35.66 | (18.93) | 40.70 | (20.46) | 0.77 (0.58-1.02) | 0.60 (0.27-1.31) |
Social functioning | 49.82 | (24.74) | 47.25 | (26.03) | 52.16 | (23.39) | 0.82 (0.62-1.08) | 1.24 (0.62-2.46) |
Mental health | 54.27 | (22.15) | 52.04 | (21.59) | 56.29 | (22.55) | 0.82 (0.63-1.08) | 1.38 (0.55-3.46) |
Role emotional | 27.46 | (37.36) | 23.66 | (35.23) | 30.90 | (39.03) | 0.82 (0.62-1.08) | 0.94 (0.55-1.61) |
Vitality | 22.29 | (16.21) | 21.55 | (16.96) | 22.95 | (15.54) | 0.92 (0.70-1.20) | 1.20 (0.72-1.99) |
General health | 40.17 | (19.46) | 38.10 | (20.87) | 42.05 | (17.97) | 0.81 (0.62-1.07) | 0.99 (0.51-1.92) |
PCS* | 36.67 | (9.92) | 35.31 | (9.91) | 37.91 | (9.81) | 0.77 (0.58-1.01) | 1.47 (0.17-12.75) |
MCS* | 36.75 | (12.58) | 35.75 | (12.78) | 37.67 | (12.39) | 0.86 (0.65-1.13) | 0.69 (0.12-3.99) |
HUI2* | 61.94 | (10.80) | 59.95 | (10.96) | 63.76 | (10.37) |
0.69 (0.52-0.92)
| Not included |
SI | Per SD increment | Per SD increment | ||||||
SI_CFS | 49.03 | (16.60) | 50.20 | (15.94) | 47.97 | (17.17) | 1.15 (0.87-1.50) | 0.68 (0.42-1.11) |
SI_NCFS | 36.98 | (18.68) | 39.95 | (19.63) | 34.24 | (17.40) |
1.37 (1.03-1.82)
| 1.47 (0.93-2.32) |