5.7Chronic Fatigue

5.7.1Fatigue at follow up

In the follow up study questionnaire, participants were asked whether they had experienced extreme tiredness or fatigue following normal activities in the previous 12 months and whether they had experienced prolonged fatigue (extreme tiredness or fatigue of at least one month’s duration) in the previous 12 months and chronic fatigue(extreme tiredness or fatigue of at least six month’s duration)in the previous 12 months. These questions comprised a subset of a larger structured questionnaire administered by the assessing doctor in the baseline study medical assessment. The Chalder Fatigue Scale (CFQ)47was used as an additional measure of fatigue, but in the follow up study only.

Extreme tiredness or fatigue, prolonged fatigue and chronic fatigue at follow up

Figure 20and Table 36show the prevalence of participants who reported fatigue related outcomes in the past 12 months at follow up. Gulf War veterans reported all of the fatigue outcomes in the past 12 months statistically significantly more commonly than did the comparison group, with the risk in Gulf War veterans estimated to be between 37% and 41% higher than that in the comparison group (Table 36).

Figure 20 Percentage of participants who reported extreme tiredness or fatigue, prolonged fatigue (at least 1 month duration) or chronic fatigue (at least 6 months duration) in the past 12 months

Table 36 Prevalence and Risk Ratios for fatigue, prolonged fatigue and chronic fatigue at follow up

Fatigue outcome in the past 12 months / Gulf War veterans
N=697 / Comparison group
N=659
n (%) / n (%) / RR / Adj RR (95% CI)
Extreme tiredness/fatigue in past 12 months / 228 (32.8) / 150 (22.9) / 1.43 / 1.38 (1.15-1.65)
Prolonged fatigue (≥ 1 month) / 117 (16.9) / 74 (11.3) / 1.49 / 1.37 (1.04-1.80)
Chronic fatigue (≥ 6 months) / 86 (12.4) / 53 (8.1) / 1.53 / 1.41 (1.02-1.96)

Fatigue severity assessed using the Chalder Fatigue Scale at follow up

Table 37 shows that the median total CFQ scores, and the median Physical- and Mental-fatigue component scores, each indicative of severity, were very similar between the two study groups. However, a greater proportion of Gulf War veterans (33%) than comparison group participants (26%) were defined as CFQ cases. This difference between groups was significant with the risk of CFQ caseness estimated to be 23% higher in Gulf War veterans than in the comparison group.

Table 37Chalder Fatigue Scale (CFQ) fatigue scores and caseness by study group

Chalder Fatigue Scale measure / Gulf War veterans
N= 697 / Comparison group
N= 659
Median (IQR) / Median (IQR) / Adj Median diff (95% CI)
Total fatigue score / 12 (11-16) / 11 (11-15) / 0.5 (0.01–0.99)
Physical fatigue score / 7 (7-11) / 7 (7-9) / 0 (-0.31, 0.31)
Mental fatigue score / 4 (4-6) / 4 (4-5) / 0 (-0.07, 0.07)
n (%) / n (%) / AdjRR (95% CI)
CFQ fatigue caseness / 232 (33.3) / 170 (25.8) / 1.23 (1.04–1.45)

5.7.2Association between Gulf War deployment characteristics and chronic fatigue in veterans at follow up

The associations between Gulf War deployment characteristics and chronic fatigue at follow up in male Gulf War veterans are shown inTable 38. In general, the risk of chronic fatigue was highest in Army Gulf War veterans relative to the Navy and Air Force, and amongst those veterans who served under non-supervisory ranks relative to higher ranks, however these differences did not achieve statistical significance. Age at the time of the Gulf War deployment was also not associated with chronic fatigue at follow up.

Table 38 Association between Gulf War-deployment characteristics and chronic fatigue at follow up in male Gulf War veterans

Gulf War exposure / Gulf War veterans with chronic fatigue
Age at deployment / N / n (%) / RR / Adj RR (95% CI)
< 20 / 62 / 9 (14.5) / 1.00 / 1.00
20-24 / 170 / 25 (14.7) / 1.01 / 1.18 (0.57-2.42)
25-34 / 364 / 41 (11.3) / 0.78 / 1.11 (0.48-2.55)
>=35 / 100 / 11 (11.0) / 0.76 / 1.07 (0.40-2.90)
Service branch
Navy / 599 / 76 (12.7) / 1.00 / 1.00
Army / 45 / 7 (15.6) / 1.22 / 1.35 (0.63-2.86)
Air Force / 52 / 3 (5.8) / 0.45 / 0.50 (0.16-1.54)
Rank category
Officer / 148 / 16 (10.8) / 1.00 / 1.00
Other rank-supervisory / 354 / 39 (11.0) / 1.02 / 0.99 (0.56-1.74)
Other rank - non supervisory / 193 / 31 (16.1) / 1.49 / 1.43 (0.70-2.91)

5.7.3Change in prevalence, also persistence, remittance and incidence of chronic fatigue since baseline

In male participants who completed questions relating to fatigue outcomes at baseline and follow up (697 Gulf War veterans and 659 comparison group) Table 39 shows that the prevalence of prolonged fatigue and chronic fatigue more than doubled from baseline to follow up, and these increases were statistically significant.

Additional analysis showed that there was no difference between the two groups with respect to change over time for prolonged fatigue (RR=0.88; 95% CI 0.55-1.39) or chronic fatigue (RR=0.76; 95% CI 0.43 – 1.35).

Table 39 Prevalence of prolonged fatigue and chronic fatigue at baseline and follow up

Gulf War veterans (N=697) / Comparison Group (N=659)
Baseline prevalence n (%)* / Follow up prevalence n (%) / RR(95% CI) / Baseline prevalence n (%)* / Follow up prevalence n (%) / RR(95% CI)
Prolonged fatigue / 50 (7.3) / 117 (16.9) / 2.32 (1.77–3.05) / 26 (4.3) / 74 (11.3) / 2.66 (1.82–3.88)
Chronic fatigue / 41 (6.0) / 86 (12.4) / 2.08 (1.52–2.85) / 18 (3.0) / 53 (8.1) / 2.72 (1.68–4.39)

* Includes only those participants who wereassessed for fatigue at follow up

Table 40 shows the proportion of Gulf War veteran and comparison group participants with chronic fatigue present or absent at baseline and at follow up. Incident cases are shown in the first row of data in Table 40 as absent at baseline and present at follow up. Of the 643 Gulf War veterans and 582 comparison group participants who had not reported chronic fatigue at baseline, 10.4% and 7.4%, respectively, were incident cases who met criteria for chronic fatigue at follow up. This difference between groups in incidence risk was not statistically significant.

Persistent cases are shown in the second row of data in Table 40 as present at baseline and present at follow up, whilst remitted cases are present at baseline and absent at follow up. Of the 41 Gulf War veterans and 18 comparison group members who had reported chronic fatigue at baseline, 18 (43.9%) Gulf War veterans and 7 (38.9%) comparison group participants were persistent cases who also reported chronic fatigue at follow up, whereas 56.1% and 61.1% remitted. The differences in persistence and remittance, between the Gulf War veterans and the comparison group,were not statistically significant.

Table 40 Persistent, remitted and incident cases of chronic fatigue among participants at baseline and follow up

Chronic fatigue / Gulf War veterans (N=682) / Comparison group (N=597)
Follow up / Follow up
Baseline / n (%)
absent / n (%)
present / Baseline / n (%)
absent / n (%)
present
Absent (n = 643) / 576 (89.6) / 67 (10.4)* / Absent (n = 582) / 539 (92.6) / 43 (7.4)*
Present(n = 41) / 23 (56.1)†† / 18 (43.9)† / Present (n = 18) / 11 (61.1)†† / 7 (38.9)†
Between groups
RR / Adj RR / 95% CI
Incidence / 1.41 / 1.36 / 0.94 – 1.97
Remittance / 0.92 / 1.08 / 0.71 – 1.65
Persistence / 1.13 / 0.87 / 0.46 – 1.66

* Incident cases
† Persistent cases
†† Remitted cases

5.7.4Key findings

All fatigue related outcomes in the past 12 months; extreme tiredness or fatigue, prolongedfatigue of at least one month duration, and chronic fatigue of at least six months duration; were increased in Gulf War veterans at follow up relative to the comparison group, based on the same definitions that were used at baseline. Furthermore, fatigue caseness was also increased as defined by the Chalder Fatigue Scale although fatigue severity was similar between the study groups.

The prevalence of prolonged fatigue and chronic fatigue more than doubled in both groups at follow up compared with baseline. Amongst Gulf War veterans there was a greater incidence of new chronic fatigue cases since baseline than in the comparison group, however this difference was not statistically significant, while remittance and persistence were similar in the two groups. There was no clear association between chronic fatigue at follow up and Gulf War-related service branch, rank or age category.

Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015 Page 1