Participants

The target group was a stratified sample of the cohort who completed the stage 1 Health Survey of Military Personnel (n=8195). This cohort consisted of three groups: personnel who served in the Persian Gulf region between 1 September 1990 and 30 June 1991 (the Gulf Cohort); personnel who had served in Bosnia between 1 April 1992 and 6 February 1997 (the Bosnia cohort); and personnel who were serving in the armed forces on 1 January 1991 but who were not deployed to the Gulf conflict (the Era cohort). Special forces were excluded for security reasons. Two stratification variables were used: fatigue and gender.

We were primarily interested in examining the health of Gulf veterans. At stage 1, fatigue, along with being strongly associated with other health outcomes measured, was one of the most consistently reported symptoms in Gulf veterans, and was our a priori principal outcome measure, and the basis for the stratified sample strategy. In order to ensure that the most severely ill were well represented, all male veterans with a fatigue score of 9 or more (511 Gulf, 115 Bosnia and 120 Era were included). A 1:2 sample of male Gulf veterans with mid-range fatigue scores of 4–8 (484 veterans) along with all Bosnia veterans (n=333) and Era veterans (n=364) scoring in this range were selected. Finally, a 1:8 sample of veterans with fatigue scores less than 4 was selected in order to represent asymptomatic individuals (250 in each group). All female veterans who completed the stage 1 questionnaire (n=648) were contacted, as women were oversampled in the original cohort. This also allowed us to look for any gender differences in follow-up variables. The total sample size was 3322.

Ethical approvals were obtained for all stages of the study. All respondents at stage 1 gave signed consent to later follow-up.

Questionnaire

The questionnaire mainly replicated the measures used at stage 1, including demographic details (age, gender, marital and educational status, alcohol and smoking habits), chronic fatigue scale, medical symptoms (50 items), self-reported medical disorders (39 items), the 12-item General Health Questionnaire (Reference GoldbergGoldberg, 1972), and the 36-item Medical Outcomes Study Short Form (SF-36) sub-scales for physical health, health perception and functional capacity (Reference Stewart, Hays and WareStewart et al, 1988).

As detailed in the original study report (Reference Unwin, Blatchley and CokerUnwin et al, 1999) we created a brief measure labelled ‘post-traumatic stress reaction’ (PTSR). This was embedded in the wider questionnaire because we did not wish to have an overt PTSD scale, given the social context of ‘Gulf War syndrome’ at the time among the UK service community and also because of the need to keep measures to a minimum. Full details of this are contained elsewhere, but in essence it consisted of four simple stem questions covering the basic psychopathological features of PTSD (Reference Unwin, Blatchley and CokerUnwin et al, 1999).

Military exposure history was investigated using the same checklist as at stage 1, again tailored for the appropriate deployment. In practice this meant that the Bosnia and Era groups were not asked about the following exposures specific to the Gulf War: smoke from oil-well fires; mustard gas or other blistering agents; having a Scud missile explode in the air or on the ground within 1 mile; hearing chemical alarms sounding; and chemical/nerve gas attack. The questionnaires were tailored according to whether the participant was still in service or not, as ascertained at stage 1.

Analyses

The reliability of the responses for each exposure at the two time points was quantified by the kappa statistic, which is a measure of the degree of non-random agreement between measurements of the same categorical variable. If the measurements agree more often than expected by chance, k is positive; if agreement is complete, k is 1; if they disagree more often than expected by chance, k is negative (Reference LastLast, 1995). A paired t-test was used to examine the number of endorsed exposures at the two time points.

We followed the same analytical approach to exposure measurements over two time points as Southwick et al (Reference Southwick, Morgan and Nicolaou1997). For each of the exposures asked about, variables were created indicating whether the exposure was:

1. (a) always endorsed at both time points (YY);

2. (b) never endorsed at either time point (NN);

3. (c) endorsed at time 1 but no longer endorsed at time 2, i.e. no longer endorsed (YN);

4. (d) not endorsed at time 1, later to be endorsed, i.e. newly endorsed (NY).

Risk factors for number of newly endorsed and no longer endorsed exposures were explored by examining their median and interquartile range (IQR). Change in health status was examined by creating a change variable (stage 3 minus stage 1) for each health outcome. This was then used as the dependent variable when exploring the effect of newly endorsed and no longer endorsed exposures on health reporting over time. The data were analysed using the Statistical Package for the Social Sciences, version 10 for Windows.

Stability of recall

There was relatively low agreement for reporting of war exposures over time, as shown by the majority of exposures having a k under 0.6. In general our findings are very similar to those of the only study that used a similar design to look at consistency of recall in smaller numbers of US Gulf War veterans (Reference McCauley, Joos and SpencerMcCauley et al, 1999). When the questions that we asked were almost identical to those asked in the US survey, the consistency of recall was likewise similar. Hence, in both studies, reporting exposure to smoke from oil fires was associated with good reliability, hearing Scuds detonate was also reasonably reliable, being aware of chemical alarms sounding was moderately reliable as was believing oneself exposed to chemical attack, whereas reporting drinking local water, exposure to chemical agent resistant coating (CARC) paint and exposure to depleted uranium was very unreliable in both studies. The recall of depleted uranium exposure is particularly problematic in the Bosnia cohort, indicated by the lowest k value (0.05). Perhaps this is a reflection of the enormous publicity given to reports of cancers occurring in peacekeepers from several European nations that happened between the two phases of our study. Likewise, chemical exposures such as CARC paint, other paints/solvents and pesticides on clothing/bedding were associated with the greatest number of ‘no’ to ‘yes’ changes (increased recall) in both Gulf and Bosnia cohorts, and correspondingly low k values. There has also been intense media concern over all these exposures in the British press in the past decade, including, but not restricted to, the military context.

Change in recall over time

Looking now at the general pattern of change, previous studies have shown that the mean number of events reported over time can either increase (Reference Southwick, Morgan and NicolaouSouthwick et al, 1997; Reference Roemer, Litz and OrsilloRoemer et al, 1998; Reference King, King and EricksonKing et al, 2000) or stay the same (Reference Bramsen, Dirkzwager and Van EschBramsen et al, 2001). Our study produced an increase in the number of events reported over time in the Gulf cohort, but no significant increase in the Bosnia cohort. What this illustrates is the importance of not assuming that all conflicts are the same in terms of their social and psychological impact. Results in our peacekeeping cohort are similar to those of Bramsen and colleagues looking at Dutch peacekeepers, and our Gulf results, although different from those in the peacekeepers, are similar to the findings of Southwick and colleagues in US Gulf veterans. On the other hand, neither we nor Bramsen et al (Reference Bramsen, Dirkzwager and Van Esch2001) are able to confirm the substantial increase in reporting of events recorded by Roemer et al (Reference Roemer, Litz and Orsillo1998) in US peacekeepers in Somalia. However, the US operation in Somalia was beset by difficulties, and involved rather more than peacekeeping, with periods of actual combat.

A second reason why the literature is not entirely consistent is that previous studies have been concerned with either post-traumatic type events and symptoms, or more ‘toxic’ hazards, but rarely with both. In our Gulf studies we have always taken a broader view of hazards and exposures, incorporating exposures such as vaccinations, smoke from oil fires, depleted uranium and so on, which are not traumatic in the customary use of the word, but certainly came to prominence after the 1991 Gulf War. This means that we included more measures of these kinds of hazards than the other studies, but conversely our measure of post-traumatic stress symptoms is less sophisticated.

Recall of exposures and current health perception

We found an association between health perception and both increased reporting and also forgetting of exposures, but this was not true of psychological morbidity or physical health. This association held for the Gulf cohort, but not for the Bosnia cohort. In general we found that the main pattern of change was of increased reporting (‘no’ to ‘yes’) rather than forgetting (‘yes’ to ‘no’).

There may be several explanations for changes in reporting of an event over time. The recall of events might simply become inflated over time; conversely, individuals might have underestimated their reports initially and later given more accurate appraisals. Over the specific interval of this study, there was considerable media attention to the Gulf War and its possible health effects. No doubt this information was incorporated to some lesser or greater degree into the participants’ perspectives on their experiences of the war. The acquisition of new knowledge, from whatever source, could explain both types of changes in item endorsement: elucidating and clarifying events and circumstances that did occur but were not previously known (accounting for ‘no’ to ‘yes’ changes), and delimiting details of experiences previously held to be true (accounting for ‘yes’ to ‘no’ changes). We should also be careful not to assume that changes in reporting equate with changes in memory – it might be that events previously seen as irrelevant and not endorsed on a questionnaire have increased in importance and salience over time, perhaps because of media coverage, rather than being newly remembered. On the other hand, there is evidence from this study that the reporting of events is influenced by current health perception. We found an association between changes in endorsement – both positive and negative – of hazards, and current health perception. Remembering more exposures over time was associated with worsening perception of health; conversely, improved perception of health was associated with forgetting previously recalled exposures. This pattern held after we had removed exposures specific to the Gulf War from the analysis, indicating that the finding was not due to certain key Gulf War exposures that might be strongly associated with health. This finding was not replicated with measures of mental health in general, or PTSD symptoms in particular.

Another important finding is that the association between health perception and recall or non-recall of hazards and exposures was found in the Gulf cohort but not in the Bosnia cohort. This was not because of a differential effect of exposures only encountered in the Gulf and also the subject of intense media scrutiny, since removing these Gulf-specific exposures did not alter the association.

We draw attention to the finding that, contrary to our original predictions, change in recall of exposures was not associated with changes in post-traumatic stress symptoms, but with health perception. However, this is in keeping with our own nested case–control study in which we interviewed both ill and healthy veterans, this time using a standardised psychiatric interview to enable us to make firm diagnoses of PTSD, which was not the case in the epidemiological study. Although psychological morbidity was increased, modestly, in the Gulf cohort, this was rarely due to PTSD (Reference Ismail, Kent and BrughaIsmail et al, 2002). This is unsurprising. The Gulf War was not particularly traumatic in the conventional sense for the coalition forces, particularly in the context of past military campaigns that were associated with high rates of classic war-related psychiatric injury. The perceived hazards of the Gulf tended to be those not usually associated with the military setting, and not encapsulated in the formulations of PTSD. Instead, most revolved around fears of environmental exposure and contamination. We have argued elsewhere that the indisputable increase in ill health seen after the Gulf War is better understood as part of the literature on unexplained symptoms and syndromes, rather than conventional PTSD. This may help to explain why changes in recall of exposures were associated more with changes in health perception than with symptoms of post-traumatic stress.

CLINICAL IMPLICATIONS

1. ▪ Stability of recall of hazardous exposures during military operations differs according to the nature of the exposure – those extensively publicised in the media are particularly problematic.

2. ▪ The number of exposures recalled has increased with the passage of time.

3. ▪ The total number of hazardous exposures reported may reflect not only actual exposures but also current distress.

LIMITATIONS

1. ▪ All military conflicts differ in various ways – it cannot be assumed that these findings extrapolate beyond the 1991 Gulf War.

2. ▪ The measurement of self-reported exposures was fairly crude.

3. ▪ Measurement of post-traumatic symptoms was by self-report and not by structured interview.