CIDI-Defined 12-Month Major Depression at Follow Up

5.15Depression

5.15.1Depression at follow up

A number of data sources were used to determine whether or not a participant was likely to have had depression in the 12 months prior to the follow up study. These include the CIDI, PBS and RPBS linkage, and self-reported doctor diagnosis and treatment from the postal questionnaire. Figure 29 shows the percentages of participants who possibly have current depression based on these measures.

CIDI-defined 12-month major depression at follow up

Sixty-three (9.7%) Gulf War veterans and 47 (7.7%) comparison group participants met CIDI criteria for 12 month major depression. This difference between groups at follow up was not statistically significant (RR 1.3, adj RR = 1.2, 95% CI 0.8 - 1.7).

Prescribed anti-depressant medications recorded on the PBS and RPBS

Data received from the PBS and/or RPBS showed that 11.2% of Gulf War veterans and 6.5% of comparison group members had been dispensed a medication listed under the ATC code NO6A for anti-depressivesin the 12 month period prior to the study. This difference between groups at follow up was statistically significant, with Gulf War veterans around 56% more likely to have been dispensed an anti-depressant medication (RR 1.73, adj RR = 1.56, 95% CI 1.05 - 2.32).

Self-reported doctor-diagnosed depression and treatment

In the postal questionnaire 76 Gulf War veterans (10.9%) and 57 comparison group members (8.6%)reported that a medical doctor had diagnosed them with, or treated them for, depression in the period since January 2001,and that they had been treated by a doctor for this condition in the past 12 months. This difference between groups at follow up was not statistically significant (RR 1.26, adj RR = 1.15, 95% CI 0.82 - 1.62).

Figure 29 Percentage of participants who possibly have depression based on the CIDI interview, PBS and RPBS records of scripts being dispensed for anti-depressive medications, and self-reported doctor diagnosed and treated depression in the past 12 months

Whilst the observed pattern across Figure 29 is for depression to be more likely in Gulf War veterans than the comparison group across all three measures, the only difference between groups which met statistical significance was that for the proportions of participants in each group being dispensed an anti-depressive medication under the PBS and RPBS in the 12 months prior to the study. The differences between groups in CIDI-defined 12 month depression, and in self-reported doctor diagnosed and treated depression in the previous 12 months, did not achieve statistical significance.

Severity of depressive symptoms

Depressive symptom severity at follow up was measured using the PHQ-9 in the self-report questionnaire. The resulting total scores were positively skewed with 75% of respondents scoring seven or less from a maximum total score of 27. The differencebetween groups in the median total score was small but statistically significant (Gulf War veterans’ median 3, IQR 0.5-7; comparison group median 2, IQR 0-5; adj difference 1, 95% CI 0.35 – 1.70). Figure 30 shows that Gulf War veterans were more likely to be categorised as having mild or moderate depressive symptoms, and less likely to be categorised as having minimal depressive symptoms, than the comparison group.

Figure 30 Depressive symptom severity derived from the PHQ-9 for participants at follow up

5.15.2Association between Gulf War-deployment characteristics and depression in veterans at follow up

The associations between Gulf War deployment characteristics and occurrence of CIDI-defined 12month major depression at follow up in male Gulf War veterans are shown in Table 50. An apparent difference across age category, with Gulf War veterans over 35 years at deployment half as likely to have major depression compared with veterans who were less than 20 years, was not statistically significant either with, or without, service branch and rank included in the model. There were also no significant associations between service branch, or rank category at the time of the Gulf War, and major depression at follow up.

Table 50Association between Gulf War-deployment characteristics and 12 month major depression at follow up in Gulf War veterans

5.15.3Change in prevalence, also persistence, remittance and incidence of 12 month major depression since baseline

For male participants who completed the CIDI at both baseline and follow up (n=637 Gulf War veterans and n=555 comparison group) Table 51 shows that for both groups the prevalence of 12 month major depression increased by approximately 2% from baseline to follow up, but this change over time was not statistically significant in either study group. Additional analysis showed that there was no difference between the two groups (RR 0.85; 95% CI 0.50-1.45) in regard to change over time.

Table 51 Prevalence of 12 month major depression at baseline and follow up for participants who completed the CIDI at both time points

* Includes only those participants who also completed the CIDI at follow up

Table 52 Persistent, remitted and incident cases of 12 month major depression among participants who completed the CIDI at baseline and follow up

* Incident cases
† Persistent cases
‡Remitted cases

Table 52 shows the proportions of Gulf War veteran and comparison group participants with a diagnosis (present) or without a diagnosis (absent) of 12 month major depression at baseline and at follow up. Relatively few of the large proportion (>90%) of Gulf War veterans and comparison group members who had no diagnosis of 12 month major depression at baseline, then had this diagnosis at follow up. Incident cases are shown in the first row of data in Table 52as absent at baseline and present at follow up. The percentage of incident cases was 7.5 in the Gulf War group and 6.3 in the comparison group; this difference between groups in incidence was not statistically significant. Persistent cases are shown in the second row of data in Table 52 as present at baseline and present at follow up, whilst remitted cases are present at baseline and absent at follow up. Of the 50 Gulf War veterans and 28 comparison group members who had a diagnosis of 12 month major depression at baseline, 34% and 25% respectively were persistent cases who also met this criteria at follow up, whereas 66% and 75% remitted. The differences between groups in persistence and remittance were not statistically significant.

5.15.4Key findings

More than 20 years after the Gulf War, veterans were more likely than the comparison group to report depression symptoms which were mild or moderate in severity, and less likely to report symptoms of minimal severity. Gulf War veterans were also more likely than the comparison group to have been dispensed an anti-depressive medication under the PBS and RPBS in the 12 months prior to the Follow Up study, but higher numbers of CIDI diagnosed major depression and doctor-diagnosed depression did not reach statistical significance.

At follow up, the Gulf War veterans and the comparison group were similar in regard to the change in depression prevalence (as measured by the CIDI) since baseline, and the rates of persistent, incident and remitted cases of depression since baseline. However, the pattern was such that the Gulf War veterans consistently achieved slightly poorer results on these outcomes even though statistical significance was not achieved.

There were no statistically significant associations between major depression in Gulf War veterans at follow up and Gulf War-related age, service branch or rank category.

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