Introduction

Over the past decade, there has been a continual increase in the use of Department of Veterans Affairs (VA) services for posttraumatic stress disorder (PTSD) by Vietnam era veterans, even though the war ended 40 years ago [1]. This increase in use is not only a concern for the treatment of Veterans from the Vietnam era, it may also serve as an indicator of future demand for services among veterans from more recent conflicts. While multiple factors may contribute to this increase, delayed onset of symptoms or delayed awareness of the connection between symptoms and war zone experiences may each play a prominent role. It is reasonable to expect that veteran’s perception of the onset of PTSD may motivate the timing of their decision to seek treatment.

The Diagnostic and Statistical Manual of Mental Disorders fourth edition defines delayed onset PTSD as “at least six months have passed between the traumatic event and the onset of the symptoms.” [2] The ambiguity of this description has created problems for the continuity of research in this area, especially in terms of case definition. Thus, in the current study, onset is defined as an intensification of PTSD related symptoms following return from overseas until the number and severity of symptoms reflected a potential clinically important problem, although the Veteran may not have perceived them as problematic at the time.

Prior studies of delayed PTSD have used various characterizations of delay, samples and methodologies, making comparison difficult and creating controversy on the prevalence of delay [3–6]. One systematic review of the literature reported a 38 % prevalence for delayed onset PTSD in military samples, where most cases were exacerbations or reactivations of previous symptoms [3]. Studies vary in the reported length of delay in onset, with several studies observing that delay beyond two years is rare [4, 7, 8], while another observed that 23 % of individuals experienced a delay of 20 years before disorder onset [9]. Other studies have examined the correlation between delay in onset of symptoms and negative life events occurring after traumatic warzone experiences. In two such studies, delayed onset of PTSD symptoms was associated with a greater number of negative life events compared to cases no delay [6, 10], but in a third study, no differences were observed [8].

This study expands the existing literature on the delay in onset of PTSD in several important areas. The specific timing of delayed onset of PTSD symptoms over an extended period following the Vietnam War is identified using retrospective veteran reports, information not available in prospective studies, and explores potential differences in this construct between veterans in different treatment settings [3, 8, 9]. Whereas prior studies of negative life events have associated them with the presence of PTSD [6, 10], in this study, associations between the number of negative life events and the specific length of delay are evaluated. In addition to investigating delayed onset, this study also evaluates a novel construct, delay in awareness of PTSD symptom relation to warzone stress, in order to further characterize this subject.

Methods

Sample

Data were drawn from structured interviews of Vietnam Veterans conducted by trained clinicians during two studies of specialized VA treatment programs for PTSD: a study of 554 outpatients conducted between 1989 and 1991 at six sites and a second study of 831 inpatients conducted between 1991 and 1994 at nine sites. Individuals were included if they served only in the Vietnam War zone and received a clinical diagnosis of PTSD at the time of the interview. DSM-III-R criteria for PTSD were operationalized in the outpatient sample by meeting the diagnostic cutoff score on the Mississippi PTSD Scale [11] and in the inpatient sample by meeting criteria on the Clinician-Administered PTSD Scale (CAPS) [12]. Application of these inclusion criteria left 353 veterans in the outpatient and 721 veterans in the inpatient sample. The two samples were analyzed separately due to differences in the content and location of treatment programs.

Measures

Queries on the date of onset and awareness of symptoms were embedded in the structured interviews. Veterans were asked “In what year would you say that you first had any of these reactions, even if you weren’t consciously aware of having them at the time?” (onset) and “In what year did you first become consciously aware that the stress of the war was affecting you in this/these ways?” (awareness).

Measures to Characterize the Sample

Measures to characterize the samples included socio-demographic variables, the Mississippi PTSD Scale, the CAPS, and the Addition Severity Index (ASI) [13].

Measures Correlated to Delay in Onset and Awareness of PTSD

Continuous characteristics from the pre-military period included age at entry into the military, years of education, as well as measures of family instability [14] and antisocial behavior [15]. Dichotomous variables were marital status at military entry, race/ethnicity, use of alcohol or drugs prior to military entry, parental alcohol/drug problem, and any pre-military treatment for psychological problems.

Continuous characteristics of the military period were level of combat exposure [16], number of months served in the war zone, and peri-traumatic dissociation at the time of the war-zone trauma measured as the sum of four dichotomous items (0–4) [17]. Other measures included branch of service, and a series of dichotomous variables: reluctant entry into the military, participating in atrocities, witnessing atrocities, disciplinary action received during military service, and alcohol/drug use in the military.

Post-military characteristics were assessed by five variables: current use of alcohol and drugs as measured the Addiction Severity Index (ASI), anger at lack of support for the war by the country, anger at being made into a “killer”, and anger at society’s lack of understanding of the Vietnam Veteran. The latter three dichotomous variables were developed by authors two and three.

Negative Life Events

Eight categories of negative life events, based those outlined by Holmes and Rahe [18], which occurred after discharge from the military were surveyed: death or threat to life of a parent, spouse or child; death or threat to life of a sibling or close friend; serious illness or medical procedure to yourself or loved one; separation or divorce; serious accident to yourself or loved one; loss of home/life due to a fire or natural disaster; assault, mugging, or rape; or an unspecified negative life event. Veterans were asked to indicate how many times each category was experienced and their age at the first post-war occurrence. Responses where the age at first time of non-military stress was greater than the reported age at onset of PTSD symptoms were excluded.

Data Analysis

Delay in Onset and Awareness of PTSD Symptoms

Specific dates for exposure to trauma were not documented, thus the year of self-reported return from the warzone was designated as the marker for no delay in onset. The delay in onset of symptoms was calculated as the length of time between the year of return and the reported year of first onset of symptoms. Delay in awareness of the connection of symptoms to war-zone experiences was calculated as the length of time between the year of symptom onset and the self-reported year of awareness. Dates preceding the year of return from the war zone represented no delay.

Categorical variables for delay of onset and awareness of PTSD symptoms were created to provide a clearer interpretation of results by identifying the inflection points of the trajectories and choosing intervals that permitted inclusion of a sufficient size to yield stable estimates of the negative post-war life events. For onset of symptoms, a four-level variable was created that suited both outpatient and inpatient samples (no delay, 1–2, 3–6 years, and 7 or more years). The trajectories for delay in awareness were different between outpatients and inpatients warranting additional categorizations. The first four levels for both samples are the same as for delay in onset. For outpatients, there is a single fifth level (13 or more years), and for inpatients there are three additional levels (13–16 years, 17–20 years, and 21 or more years).

Negative Life Events

Negative life events were operationally defined as the number of negative life events, summed across the eight categories.

Statistical Analysis

The categorical variables for delay of onset and awareness were used as independent variables along with treatment program site as a control in analyses of covariance for the number of negative life events. Because of the disproportionately large size of the no delay categories compared to the sizes of the delay categories, these analyses were weighted by the inverse of the frequencies of the categories of delay. Pearson product-moment correlations were calculated for a linear association between pre-military, military and post-military characteristics with delay of onset and awareness. Due to the large number of factors surveyed, p ≤ 0.001 was adopted as the criterion for statistical significance.

Results

All participants were male. The socio-demographic and clinical characteristics of veterans in the two samples are presented in Table 1.

Table 1 Characteristics of inpatient (n = 721) and outpatient (n = 353) samples
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Delay of Onset and Awareness

The mean interval for delay in onset of PTSD symptoms, including those with no delay (49.9 % of outpatients and 64.7 % of inpatients), was 1.7 years (SD = 3.6) for outpatients and 0.7 years (SD = 2.7) for inpatients, while it was 3.1 years (SD = 4.3) for outpatients and 1.4 years (SD = 3.6) for inpatients after removing cases of no delay in onset of symptoms. The mean interval between the onset of PTSD symptoms and the awareness of their connection to the war zone experiences, including those with no delay (40.8 % of outpatients and 34.1 % of inpatients), was 5.6 years (SD = 6.8) for outpatients and 7.4 years (SD = 8.2) for inpatients, while it was 5.6 years (SD = 6.4) for outpatients and 6.8 years (SD = 7.6) for inpatients when cases with no delay were removed.

The frequency of delayed onset and awareness of symptoms over time are presented in Figs. 1 and 2. For delay in onset of symptoms, the curves for outpatients and inpatients display a parallel decrease in the proportion reporting symptom onset as time progresses with an inflection at 5–6 years, leading to a flattening of the curves with few reporting an onset up to 30 years. Taken as a percent of each population, 90.8 % of outpatients and 96.5 % of inpatients reported experiencing symptoms by 5–6 years. For onset in awareness of symptoms, the curves for outpatients and inpatients are also parallel, but show a more gradual and protracted decrease in the frequency of individuals reporting symptom awareness as time progresses compared to the symptom onset curve. Taken as a percent of each population, 92.0 % of individuals reported experiencing symptoms by 17–18 years in the outpatient sample and 90.5 % by 19–20 years in the inpatient sample.

Fig. 1
figure 1

Percent of sample experiencing delay in PTSD symptom onset

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Fig. 2
figure 2

Percent of sample experiencing delay in awareness of PTSD symptom relation to war-time experience

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Negative Life Events

The results for analyses of covariance of negative life events are presented in Table 2. For both outpatients and inpatients, a greater number of post-military negative life events displayed a statistically significant association with categories of increasing delay in both onset and awareness of PTSD symptoms.

Table 2 Association of delay in onset of PTSD symptoms and delay in awareness of PTSD symptoms with the number of negative life events after trauma
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Correlation with Pre-military, Military, and Post-military Characteristics

Most veteran characteristics did not reveal a statistically significant association (p ≤ 0.001) with delay in onset or awareness. Parental use of alcohol or drugs showed a statistically significant association (r = 0.20, p < 0.001) for outpatients but not for inpatients. With respect to military experiences, there was a significant negative correlation between level of combat exposure and delay in awareness of symptoms (r = −0.18, p < 0.001) for inpatients, but not outpatients. For outpatients, peri-traumatic dissociation was negatively correlated with delay in awareness in outpatients (r = −0.19, p < 0.001) but not for inpatient or for delay in onset of symptoms. For post-military characteristics, there were significant correlations with the number of negative life events as described above but not for other post-military variables.

Discussion

Of Veterans diagnosed with PTSD in two treatment programs, 90 % had experienced symptoms of their disorder within 5–6 years of their return from Vietnam. The awareness of symptom relation to war-zone stress was more gradual over time, whereby 90 % were aware of this relationship by 19–20 years. In both Figs. 1 and 2, the trajectory for both outpatients and inpatients was similar, suggesting the operation of analogous processes. This study also found that the number of negative life events experienced after combat trauma was associated with both longer delay in onset and awareness of symptoms. These findings suggest that the time following trauma and before the onset of symptoms or awareness of their context can be extensive and is likely a psychologically meaningful period.

Although this data was developed from Veterans’ retrospective reports, the trajectory is similar to the longitudinal psychometric assessments of Veterans’ PTSD symptoms by Solomon and Mikulincer (2006), where the onset of symptoms was delayed at least 20 years in 23 % of individuals [9]. However, in the current study onset occurred within six years in 90 % of cases with very few cases at 20 years, making the findings more similar to that reported in the retrospective study by Frueh and colleagues where there were few cases of delayed onset beyond six years [7].

This research is the first to observe an association between the number of negative life events and the specific length of delay in onset and awareness of PTSD symptoms in veterans. These findings are consistent with those reported in a study of individuals exposed to the World Trade Centers disaster, where those with delayed onset of PTSD at two years had more negative life events [10], and a study of U.K. Veterans showing that individuals with delayed onset PTSD were more likely to have a negative stressor in the year before diagnosis [6]. Taken together, it is clear that experiences in the period of time after exposure to a primary trauma and before symptom onset influence the timing of onset and awareness of PTSD.

Other Veteran characteristics displayed a somewhat spotty pattern of association with delay of onset and awareness of PTSD symptoms. There was little replication of significant associations across inpatient and outpatient samples or between delay in onset and delay in awareness. However, comparison of the current results with those of other investigators may allow for the discovery of additional variables that are associated with delay in onset or awareness of symptoms. The finding that less peri-traumatic dissociation was associated with a longer delay of awareness is consistent with that of Andrews et al. [6]. However, the findings that less exposure to combat in the war-zone was associated with a longer delay in awareness and onset, respectively, are not consistent with the findings reported by others [19, 20].

It must be noted that the current study is based on Veterans’ retrospective reports which may be susceptible to self-report bias and change over time [21] while prospective studies are based on current assessments of veterans’ health status [9]. It is unclear to what extent this methodological difference may have contributed to differences between this study and those using a prospective method. However, the variability in the length of delay found in prospective studies is an indication that other methodological differences also contribute to this process. Moreover, prospective studies have their own limitations, not found in retrospective designs. Veterans may have onsets and remissions of symptoms that occur between assessment time-points, which can be better detected by retrospective questioning [3]. In addition, retrospective studies can more easily cover long expanses of time at far lower cost since only one assessment is needed.

Other limitations that are more specific to the present study must also be addressed. Dating of traumatic events in the current study was imprecise because the measures used did not contain the specific dates the trauma occurred, only the year of return from the war zone. The adoption of the year of return from the war zone as the marker for no delay in onset assumes that the trauma exposure occurred up to six months prior to that date. Given the continuous threat posed by the insurgent nature of the enemy in Vietnam, we believe that this is a reasonable assumption. In addition, understanding if previous treatment had been specifically directed toward PTSD, as well as the number and dates of previous treatment episodes would have been preferable, allowing for more precise determination of delays in onset and awareness. Moreover, the case definition of PTSD in the two studies used different PTSD measures. However, given the strong correlation in diagnostic validity between the two measures, the use of two different is unlikely to have impacted the validity of these results [22].

The current results have implications for the anticipated treatment demand from Iraq and Afghanistan Veterans. If veterans from recent conflicts have similar rates of delayed onset of symptoms and awareness of the connection between their symptoms and war-zone stress, they are likely to present a demand for treatment services for many years following their return from combat. Unfortunately, there is no data concerning the connection between these delays of onset and awareness and the timing of the decision to seek treatment for PTSD symptoms. It is reasonable to assume, however, that the decision to seek PTSD treatment is affected by the awareness of symptoms as manifestations of PTSD and by their attribution of them to war zone stress. Moreover, it must be noted that there is currently greater awareness of PTSD, its symptoms, and evidence-based treatment options compared to the post-Vietnam era, which may decrease the delay of onset and awareness of symptoms in veterans from more recent conflicts.

In conclusion, the current study confirms that PTSD is a chronic problem for many Vietnam Veterans, and symptom manifestation is frequently affected by post-war experiences. Further retrospective studies of Vietnam Veterans and prospective studies of Veterans of Iraq and Afghanistan are needed to better understand the lifelong impact of exposure to war-related trauma.