Introduction {#sec0001}
============

The trajectories for post-traumatic stress disorder (PTSD) symptoms among people exposed to major disasters are known to evolve in complex ways ([@bib0006]; [@bib0016]; [@bib0046]). A recent review ([@bib0016]) that analyzed studies from different types of disasters, including human-made/technological disasters, natural disasters, and adult civilian traumas or accidents, showed that four trajectories were consistently identified: Resilience, never showing more than mild distress; Recovery, initially showing above threshold symptoms that decrease gradually to normal levels over time; Chronicity, showing pronounced symptoms from onset and thereafter; and Delayed onset, elevations above the diagnostic threshold that emerge following a significant delay. Although the majority of survivors initially exhibit psychological distress and/or deterioration in their functional abilities, approximately two-thirds do not require treatment from mental health professionals and show resilience, recovery, or subsyndromal (elevated symptoms below the diagnostic threshold) symptomatology ([@bib0016]; [@bib0046]). Conversely, about one-third of people exposed to the disaster exhibit chronic distress or dysfunction. Among those with chronic symptoms, some exhibit severe symptoms from the initial phase of the disaster, whereas others deteriorate over time and exhibit delayed onset or fluctuating symptoms (cyclical course moving above and below the diagnostic threshold) ([@bib0016]; [@bib0046]).

Characteristics of major disasters differ and multiple factors, including pre-, peri-, and post-disaster personal and social factors influence the consequent mental health of affected individuals, including PTSD, depression, anxiety, grief, substance abuse, suicidal ideation, and non-specific distress ([@bib0006]; [@bib0043]). Among adult survivors, demographic characteristics such as female sex and younger age are associated with adverse outcomes ([@bib0043]). One of the important factors relates to the type of disaster. Disasters caused by humans or a technological fault tend to exhibit a stronger psychological impact than that of natural disasters because human-caused disasters, such as mass violence and terrorist attacks, symbolize human callousness and carelessness ([@bib0018]; [@bib0041]; [@bib0044]). Further, the average exposure dose among study participants tended to be higher in the studies of human-made/technological disasters because in large-scale natural disasters, affected areas and populations tend to be broad, which leads researchers to include mixed populations that often consist of both direct and indirect victims ([@bib0041]). However, even in natural disasters, direct victims, such as those who lost family members or been forced to evacuate ([@bib0061]), affected people who lack social support ([@bib0008]) or exhibit ongoing stressors ([@bib0009]), and persons with a history of physical or mental illnesses are known to be at higher risk of PTSD ([@bib0008]; [@bib0043]). Additionally, the sociocultural backgrounds of the affected populations modify the mental health effects of disasters ([@bib0012]). For example, Asians have been reported to be at lower risk of developing PTSD after traumatic events ([@bib0049]). Because populations affected by major natural disasters tend to be larger than those affected by human-made/technological disasters, identification of vulnerable populations and factors related to their psychological outcomes is essential for appropriate program planning and implementation of psychological interventions ([@bib0041]).

Not only the general population but also first responders and disaster recovery workers who engage in relief activities are known to suffer from a diverse range of psychological symptoms ([@bib0003]; [@bib0004]). In particular, varying conditions, such as PTSD, acute stress disorder, depression, and anxiety disorders, have been shown repeatedly among first responders and recovery workers responding to major disasters ([@bib0003]; [@bib0004]; [@bib0055]) who may work continually to assist survivors and restore the local community during the initial phase of a disaster and may also continue to live in the vicinity as disaster survivors. These workers may not only suffer personal traumas and losses ([@bib0050]; [@bib0059]) but also experience secondary traumatic stress because of their frequent contact with other survivors, while trying to live an ordinary life in the affected location ([@bib0011]). Compared with traditional first responders, who are temporarily deployed to a disaster site, local workers confront a diverse range of stressors over a longer period of time. Previous studies have shown that in local recovery workers, mental health consequences of disasters were affected by both personal and workplace factors, such as prior psychiatric history, personal grief, financial difficulties, loss of colleagues, and longer hours spent at the disaster site ([@bib0047]; [@bib0062]).

In Japan, once a large-scale disaster occurs, local municipality workers and hospital medical workers of disaster base hospitals are supposed to engage in disaster response and recovery, which often continue for a prolonged period. For example, from immediately after a disaster, municipality workers will be involved in a variety of tasks, including management of evacuation centers, damage assessment, management of temporary morgues, disposal of disaster debris, and restoration of public services. Subsequently, these workers engage in long-term reconstruction activities, including building and managing temporary houses, restoring damaged homes, constructing infrastructure, reconstructing industry, and providing health services to victims ([@bib0036]). Medical workers of disaster base hospitals exhibit a central role in accepting and transporting injured and sick people after the disaster, and the hospitals function as headquarters for medical relief teams from different parts of Japan, including disaster dispatch medical care teams (DMATs) consisting of doctors, nurses, and medical clerks, and provide outreach emergency care for victims at the disaster site and medical care for evacuees at shelters ([@bib0021]). Outreach activities of medical teams, including DMATs, continue until local hospitals and clinics become functional again, which is often prolonged after major disasters. There have been calls to evaluate the post-disaster mental health consequences for local municipalities and medical workers and to develop adequate support ([@bib0034]; [@bib0053]).

Recently, studies on the trajectories of PTSD symptoms among first responders and recovery worker accumulated; however, all of these studies, to date, have been concerned with the World Trade Center (WTC) disaster of September 2001 ([@bib0014]; [@bib0047]; [@bib0064]), which was a human-made disaster. These studies have demonstrated that trajectories of PTSD symptoms among disaster recovery workers are diverse and that approximately 20%--30% of these workers are affected by long-term adverse mental health outcomes classified as chronic or delayed-onset trajectories. However, the PTSD symptoms in recovery workers with different sociocultural backgrounds who respond to large-scale natural disasters remain unclear.

With regard to the GEJE, previous cross-section studies concerning PTSD symptoms in first responders ([@bib0015]; [@bib0042]) and recovery workers ([@bib0050]; [@bib0054]) have revealed a relatively low prevalence of probable PTSD among these workers. However, the, longitudinal progression and diversity of their PTSD symptoms and the factors related to ongoing PTSD symptoms remain to be clarified. Group-based trajectory modeling ([@bib0039]) is one of the useful approaches for elucidating the heterogeneous trajectories of PTSD symptom after exposure to major disasters; it enables clinicians to estimate the proportion of workers who require prolonged support. This information along with information about potentially modifiable risk factors is essential for mental health professionals and policymakers who plan and implement mental health intervention for first responders and disaster recovery workers.

The aim of this study was to identify and describe the trajectories of PTSD symptoms among local disaster recovery workers following the GEJE disaster. Recognition of the trajectories of PTSD symptoms and risk factors related to each trajectory will contribute to developing specific countermeasures to protect the mental health of these local workers.

Methods {#sec0002}
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Great East Japan Earthquake (GEJE) {#sec0003}
----------------------------------

The GEJE struck the Northeastern part of Japan on March 11, 2011. It was one of the largest earthquakes ever recorded in Japan, measuring 9.0 on the Richter scale. The earthquake triggered a huge tsunami, killing more than 18,000 people and destroying approximately 400,000 houses. In the Miyagi prefecture, which was closest to the earthquake\'s epicenter, more than 10,000 lives were lost. All of the cities and towns along the coastal regions of the prefecture were severely damaged ([@bib0036]). Because such a large area was devastated by the GEJE, the process of local community reconstruction faced many difficulties and was delayed at length. More than 20,000 people were forced to live in prefabricated temporary housing 5 years after the disaster ([@bib0037]).

Participants {#sec0004}
------------

In this prospective observational study, PTSD symptoms and associated factors were assessed among local municipality workers and medical workers (i.e., doctors, nurses, pharmacists, medical technologists, midwives, and ancillary medical personnel) of the disaster base hospital of district A, located in the coastal area of Miyagi prefecture. Participants were recruited at the time of the annual health survey at each workplace. The area was among the hardest hit by the tsunami; approximately 2% of the population was lost, and \> 30% of the houses collapsed entirely ([@bib0040]). The damage experienced here was much higher than the average seen in Miyagi prefecture (0.5% of the population lost; 9% of houses totally collapsed) ([@bib0040]). After the GEJE, municipality workers of the affected areas had been involved in large-scale and multi-year post-disaster reconstruction activities in addition to their ordinary duties, and chronic staff shortages afflicted municipality offices in the affected areas ([@bib0030]). Exhaustion of medical workers has also been a concern. Disaster relief activities by the medical workers and medical relief teams lasted for as long as 6 months. After relief activities, disaster-based hospitals were overwhelmed with an increase in emergency patients and outpatients even 12 months after the GEJE because most local hospitals and clinics in the affected area were damaged by the disaster, and approximately 30% of them were permanently closed ([@bib0023]).

Using self-administered questionnaires, the study was conducted at four time points after the GEJE: 14 months (wave 1), 30 months (wave 2), 43 months (wave 3), and 54 months (wave 4).

Of all the 1,335 workers who were employed in the local municipalities or disaster base hospitals of district A at the time of wave 1, 1,233 (92.4%) were eligible to participate in the surveys. The 102 (7.6%) workers who started working after the GEJE were not included in the study. To maintain the longitudinal aspect of the analysis, the inclusion criteria of the study were workers who responded to the first and more than one of the subsequent three surveys, and therefore, workers who did not participate in wave 1 or those responding only in wave 1 were excluded from the study. A total of 939 workers (76.2% of eligible workers) participated in the wave 1 survey, and among them, 745 workers \[60.4% of eligible workers consisting of local municipality workers (n = 434) and hospital medical workers (n = 311)\] participated in at least one of the subsequent three surveys and were thus included in the study. The mean age of the participants in wave 1 was 43.6 ± 9.5 (range: 20 -- 66) years and 306 (59%) participants were women.

Measurements {#sec0005}
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### Demographic characteristics {#sec0006}

In wave 1, the demographic characteristics (age, sex), personal risk factors, "displacement", "dead or missing family members", and "near-death experience" were surveyed because direct exposure to a disaster has been consistently associated with increased risk of PTSD ([@bib0018]). Additionally, "pre-disaster treatment for physical illness" and "pre-disaster treatment for mental illnesses" were surveyed because prior history of physical and mental illnesses have been repeatedly shown to be important risk factors for increased risk of PTSD as well ([@bib0008]; [@bib0043]). Workplace factors, such as "supervisory work status," were surveyed because higher status with more responsibility may be a stressor after disasters ([@bib0026]). To assess exposure related to the workplace, "mainly disaster-related work" and "dead or missing colleague(s)" were surveyed ([@bib0018]). To assess general distress at current workplace, "lack of communication" and "lack of rest" were surveyed because ongoing stressors have been associated with post-traumatic stress after a disaster ([@bib0010]; [@bib0017]). All questions about personal and workplace factors only required a "yes" or "no" answer ([Table 1](#tbl0001){ref-type="table"} ).Table 1Participant characteristics at the first survey (n = 745)Table 1N%**Sex**Female43958.9Male30641.1**Age (years)**20--3927036.240--5947463.660+10.1**Workplace factors**Supervisory work status739.8Mainly disaster-related work [a](#tb1fn1){ref-type="table-fn"}17022.8Lack of communication [b](#tb1fn2){ref-type="table-fn"}15120.3Lack of rest [c](#tb1fn3){ref-type="table-fn"}34045.6Dead or missing colleague(s)12416.6**Personal factors**Displacement [d](#tb1fn4){ref-type="table-fn"}17723.8Dead or missing family members(s)476.3Near-death experience [e](#tb1fn5){ref-type="table-fn"}40854.8Pre-disaster treatment for physical illness16822.6Pre-disaster treatment for mental illness314.2**Probable PTSD (PCL-S ≥ 44)**14 months (n = 745)628.330 months (n = 505)234.643 months (n = 524)254.852 months (n = 582)315.3[^1][^2][^3][^4][^5][^6][^7]

### Risk factors {#sec0007}

Personal factors were as follows: (1) "displacement"---whether the worker was displaced from prior housing to temporary or another type of housing (e.g., a relative\'s house) because of the damage caused by the earthquake or tsunami; (2) "dead or missing family member(s)"---whether a worker\'s family member was killed or still missing; (3) "near-death experience"---whether the worker had experienced a life-threatening situation due to the earthquake or tsunami; (4) "pre-disaster treatment for physical illness"---whether the worker received medical treatment for physical illness just prior to the GEJE; and (5) "pre-disaster treatment for mental illness"---whether the worker received treatment for mental illness just prior to or at any time before the GEJE.

Workplace factors were as follows: (1) "supervisory work status"---whether the worker\'s position was higher than that of a manager; (2) "mainly disaster-related work"---whether the worker subjectively felt that they spent more than half of his or her occupational effort on disaster-related duties for the previous 14 months (i.e., since the earthquake); (3) "dead or missing colleague(s)"---whether the worker\'s colleagues were killed or still missing; (4) "lack of communication"---whether the worker felt at the time of survey that workplace communication was lacking; and (5) "lack of rest"---whether the worker felt at the time of survey that he or she was not obtaining sufficient rest because of occupational duties.

All the factors were assessed at wave 1, except for pre-disaster treatment for physical and mental illnesses, which were assessed at waves 2 and 3. Data from wave 2 were used for analysis of participants who completed both waves 2 and 3 or those who completed only wave 2, whereas data from wave 3 were used for analysis of participants who completed only wave 3.

### Outcomes {#sec0008}

The severity of PTSD symptoms was measured using the Japanese version of the PCL-S adapted to be specific to the GEJE, of which reliability and validity have been confirmed ([@bib0022]; [@bib0058]). The PCL-S is a widely used questionnaire to assess the severity of PTSD symptoms among people who experienced a specific traumatic event ([@bib0035]; [@bib0063]). The PCL-S consists of 17 items corresponding to DSM-IV PTSD symptoms criteria B (re-experiencing), C (avoidance/numbing), and D (hyperarousal) ([@bib0001]). Each item contains a Likert-type response format ranging from 1 ("not at all") to 5 ("extremely"), and the total score ranges from 17 to 85. A cutoff score was set at ≥ 44 to indicate probable PTSD ([@bib0005]). Cronbach\'s alpha values for the four waves were 0.953, 0.939, 0.945, and 0.952.

### Ethical issues {#sec0009}

The data used in this study were acquired during health examinations conducted by each workplace. To protect the privacy of the participants, the questionnaire was distributed and collected within each workplace by the person who oversaw the health of staff members. We obtained the electronic data but not personal information. Therefore, we could not obtain written informed consent from each participant. Instead, we disclosed the study information, including the objectives and procedure, to the subjects and provided them with the opportunity to refuse participation. All of the participants who completed and returned the questionnaires were deemed as having consented to the study. Moreover, the names of administrative regions, cities, or towns were anonymized so that the workplaces of the participants were not specified. The study protocol and consent procedure were reviewed and approved by the Ethics Committee of Tohoku University Graduate School of Medicine (reference number: 2012-1-197).

Data analysis {#sec0010}
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### Group-based trajectory modeling {#sec0011}

Group-based trajectory modeling is a type of growth mixture modeling used to identify distinct subpopulations showing similar progressions in their symptoms or behaviors ([@bib0038]; [@bib0039]). Various researchers conducted group-based trajectory modeling to elucidate progression of psychological symptoms over time, including studies of PTSD symptoms among disaster responders and recovery workers at the WTC disaster ([@bib0047]; [@bib0064]).

Missing values for the total score of PCL-S \[wave 2, 240 (32.3%) cases; wave 3, 221 (29.7%) cases; wave 4, 163 (21.9%) cases\] were imputed using a multiple imputation method and the MI procedure in SAS version 9.4 software (SAS Institute Inc., Cary, NC) under the assumption that data were randomly missing ([@bib0067]). To mitigate selection bias, the MI procedure creates 25 imputed datasets and the first dataset was used to perform subsequent group-based trajectory modeling.

We performed group-based trajectory modeling using the PROC TRAJ procedure in SAS ([@bib0024]; [@bib0025]), based on the tutorial by Andruff et al. ([@bib0002]), to identify distinct subgroups with similar patterns of GEJE-related PTSD symptoms over time. The analysis started with modeling a single group trajectory, with a cubic specification for trajectory shape and dropped non-significant polynomial terms; the model of each additional trajectory was compared with the previous model until no substantial improvement in the model fit existed. The better model fit was based on an estimate of the log Bayes factor ([@bib0002]), which is calculated by doubling the remainder after subtracting the sample-size adjusted Bayesian information criterion (SSA-BIC) value of the simpler model (i.e., the model with the smaller number of trajectories) from the more complex model (i.e., the model with the larger number of trajectories). Values greater than 10 were interpreted as very strong evidence for a better fit. In addition, entropy (average posterior probabilities of group membership, \> 80%), parsimony, and interpretability of our participants were also considered ([@bib0002]). Each participant was assigned to the group for which their average posterior probability was greatest. Descriptive analysis of demographic characteristics was also performed using SAS.

Next, we performed χ2 tests with categorical variables and analysis of variance with continuous variables to explore whether the participants' characteristics differed between the PTSD symptoms trajectory groups. For post-hoc multiple comparison, we performed an adjusted standardized residuals (ASRs) analysis for χ^2^ tests and Bonferroni correction to control for type I error in analysis of variance. ASRs greater or less than ±2.0 are considered to be significantly higher or lower (p \< 0.05) than chance ([@bib0033]). A two-sided p-value \< 0.05 was used to indicate significance. We reported our study using the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline ([@bib0013]) and Guidelines for Reporting on Latent Trajectory Studies (the GRoLTS-Checklist) ([@bib0060]).

Results {#sec0012}
=======

Of 939 workers who participated in wave 1, 745 workers who responded to more than one of the subsequent three surveys were included in this study (an overall comparison between the included and excluded participants is shown in Supplementary Table 1). The mean score of the PCL-S at wave 1 among the subjects included in this study (n = 745, 28.0 ± 11.0) did not differ from that of the subjects excluded from the study (n = 194, 27.4 ± 10.2) (t = 0.72, p = 0.47). Compared with the participants included in the analysis, the excluded participants were older (t = 5.2, p \< 0.001) and were more likely to have factors of supervisory work status (χ^2^ = 14.15, p \< 0.001) and dead or missing family members(s) (χ^2^ = 8.09, p \< 0.01). Of the 745 subjects included in the study, 505 (67.8%), 524 (70.3%), and 582 (78.1%) participated in wave 2, wave 3, and wave 4, respectively. The number of participants completing all waves was 274 (29.2% of the participants at wave 1).

[Table 1](#tbl0001){ref-type="table"} describes the demographic profile, workplace, and personal attributes of disaster workers. Of 745 workers \[average age: 43.6 (± 9.5, range: 20 -- 66) years; 306 (59%)women\], 24% were forced to evacuate their original houses, and 55% experienced fear of death because of their involvement in the GEJE. Overall, the percentage of participants with possible PTSD (PCL-S ≥ 44) ([@bib0005]) was 8.3% (highest) in wave 1 (14 months) and dropped to 4.6% in wave 2 (30 months). The percentages remained stable through waves 3 (43 months) and 4 (54 months) at 4.8% and 5.3%, respectively.

[Table 2](#tbl0002){ref-type="table"} describes the fit indices calculated for each model (Akaike information criterion, AIC; BIC; SSA-BIC, estimated log Bayes factor, entropy, number and percentage of participants assigned to each group). Trajectory model 5 exhibited the best fit statistics (SSA-BIC = −9763.56, estimated log Bayes factor = 108.5, entropy = 0.93) relative to those of trajectory models 4 (SSA-BIC = −9810.80, estimated log Bayes factor = 135.6, entropy = 0.93) or 6 (SSA-BIC= −9785.87, estimated log Bayes factor = −12.3, entropy = 0.93). The average posterior probabilities of each trajectory in trajectory model 5 were between 86 and 98% and were higher than the above-mentioned criteria (80%); therefore, we selected trajectory model 5 as final and most parsimonious ([Figure 1](#fig0001){ref-type="fig"} ).Table 2Fit information for the group-based trajectory modelTable 2ModelAICBICSSA-BICEstimated Log Bayes FactorEntropyGroup 1 n (%)Group 2 n (%)Group 3 n (%)Group 4 n (%)Group 5 n (%)Group 6 n (%)1−10722.7−10734.7−10731.9−1745 (100.0)\-\-\-\--2−10072.1−10102.1−10095.21301.00.98632 (84.0)113 (16.0)\-\-\--3−9832.6−9865.6−9858.0479.10.96531 (70.7)175 (24.1)39 (5.3)\-\--4−9764.8−9812.8−9801.7135.60.93482 (64.1)172 (23.3)53 (7.4)38 (5.2)\--5−9710.5−9779.5−9763.6108.50.93467 (62.3)181 (24.2)47 (6.8)26 (3.6)24 (3.2)-6−9716.7−9806.7−9785.9−12.30.93466 (62.1)180 (24.4)47 (6.6)28 (3.7)24 (3.2)0 (0.0)[^8]Figure 1Trajectories of post-traumatic stress disorder (PTSD) symptoms among local disaster recovery workers following the Great East Japan Earthquake (n = 745)Note. PCL-S; PTSD Checklist specific version. Total score of PCL-S ranges from 17 to 85. Gray area represents the 95% confidence interval for each trajectory. Names of the trajectories are based on patterns observed during the study period (14--54 months after the GEJE) and careful interpretation is therefore necessary. For example, participants whose trajectory was classified as "resistance" may not have been resilient immediately after the disaster.Figure 1

[Table 3](#tbl0003){ref-type="table"} describes the characteristics of the participants assigned to each group: resistance (n = 467, 62.7%), never showing more than mild distress; subsyndromal (n = 181, 24.3%), elevated symptoms below the diagnostic threshold; recovery (n = 47, 6.3%), initially showing above threshold symptoms but that decreased gradually to normal level over time; fluctuating (n = 26, 3.5%), cyclical course moving above and below the diagnostic threshold, and; chronic (n = 24, 3.2%), showing pronounced symptoms from onset and thereafter.Table 3Participant Characteristics of the Post-traumatic Stress Disorder Symptoms Trajectory GroupTable 3ResistanceSubsyndromalRecoveryFluctuatingChronicN%n%n%n%n%χ^2^/Fp**Number of participants**46762.718124.3476.3263.5243.2**Average posterior probability**95.886.391.092.898.4**Sex**Female27258.210759.13166.01661.51354.21.350.853Male19541.87440.91634.01038.51145.8**Age (years)**20--3918439.45731.51327.7726.9937.50.850.49540--5928260.412468.53472.31973.11562.560+10.2**Workplace factors**[a](#tb3fn1){ref-type="table-fn"}Supervisory work status5110.9189.936.400.014.24.980.290Mainly disaster-related work [b](#tb3fn2){ref-type="table-fn"}7716.55630.92042.6830.8937.531.67\<0.001Lack of communication [c](#tb3fn3){ref-type="table-fn"}7015.04524.91531.91246.2937.529.55\<0.001Lack of rest [d](#tb3fn4){ref-type="table-fn"}17537.59954.73268.11453.82083.342.53\<0.001Dead or missing colleague(s)7516.13016.6817.0519.2625.01.450.835**Personal factors**Displacement [e](#tb3fn5){ref-type="table-fn"}9520.34927.11531.9623.11250.014.960.005Dead or missing family members(s) [f](#tb3fn6){ref-type="table-fn"}234.9116.1510.6311.5520.812.790.012Near-death experience [g](#tb3fn7){ref-type="table-fn"}22648.411060.83676.61765.41979.226.28\<0.001Pre-disaster treatment for physical illness [h](#tb3fn8){ref-type="table-fn"}8418.05128.21225.5726.91458.326.97\<0.001Pre-disaster treatment for mental illness [i](#tb3fn9){ref-type="table-fn"}102.184.4510.6415.4416.727.38\<0.001**PTSD score (PCL-S)**meanSDmeanSDmeanSDmeanSDmeanSDFpWave 1 (14 months) [j](#tb3fn10){ref-type="table-fn"}21.9(4.5)31.0(5.4)47.8(5.8)37.8(4.9)56.3(8.4)587.9\<0.001Wave 2 (30 months) [k](#tb3fn11){ref-type="table-fn"}21.0(3.4)29.0(4.8)31.6(6.5)45.4(8.1)46.5(9.2)421.3\<0.001Wave 3 (43 months) [l](#tb3fn12){ref-type="table-fn"}20.7(3.7)28.6(6.1)31.5(8.0)37.4(7.7)48.2(10.9)270.9\<0.001Wave 4 (52 months) [m](#tb3fn13){ref-type="table-fn"}20.1(3.5)28.6(6.0)28.4(6.6)45.7(8.4)48.0(9.3)387.1\<0.001[^9][^10][^11][^12][^13][^14][^15][^16][^17][^18][^19][^20][^21][^22]

As summarized in [Table 3](#tbl0003){ref-type="table"}, post-hoc analysis showed differences in multiple workplace factors, such as mainly disaster-related work (χ^2^ = 31.67, p \< 0.001), lack of communication (χ^2^ = 29.55, p \< 0.001), and lack of rest (χ^2^ = 42.53, p \< 0.001) as well as in all of the personal factors of displacement (χ^2^ =14.96, p \< 0.01), dead or missing family members(s) (χ^2^ =12.79, p \< 0.05), near-death experience (χ^2^ = 26.28, p \< 0.001), pre-disaster treatment for physical illness (χ^2^ = 26.97, p \< 0.001), and pre-disaster treatment for mental illness (χ^2^ = 27.38, p \< 0.001) across the trajectory groups. Post-hoc comparison of total PCL-S scores was performed at each wave after Bonferroni correction (p \< 0.05/10 = 0.005); at wave 1, the scores of all the groups were significantly different; at wave 2, the scores of all the groups were significantly different, except those for chronic and fluctuating; at wave 3, the scores of all the groups differed significantly; and at wave 4, the scores of all the groups were significantly different, except those for chronic and fluctuating and for recovery and subsyndromal.

Post-hoc comparison using ASRs (Supplementary Table 2), for which those greater or less than ± 2.0 indicated factors significantly (p \< 0.05) higher or lower than chance, revealed that "mainly disaster-related work" in the subsyndromal (3.0) and recovery (3.3) trajectories exhibited positive ASRs, indicating that the participants included in the subsyndromal and recovery trajectories demonstrated factors significantly greater than chance and in the resistance trajectory (−5.3) exhibited a negative ASR, indicating that the participants exhibited a factor significantly less than chance; "lack of communication" in the chronic (2.1), fluctuating (3.3), and recovery (2.1) trajectories exhibited positive ASRs and in the resistance (−4.6) trajectory exhibited a negative ASR; "lack of rest" in the chronic (3.8), recovery (3.2), and subsyndromal (2.8) trajectories exhibited positive ASRs and "in the resistance (−5.8) trajectory exhibited a negative ASR; "displacement" in the chronic (3.1) trajectory exhibited a positive ASR and in the resistant (−2.8) trajectory exhibited a negative ASR; "dead or missing family members(s)" in the chronic (3.0) trajectory exhibited a positive ASR and in the resistant (−2.0) trajectory exhibited a negative ASR; "near-death experience" in the chronic (2.4) and recovery (3.1) trajectories exhibited positive ASRs and in the resistance (−4.5) trajectory exhibited a negative ASR; "pre-disaster treatment for physical illness" in the chronic (4.3) and subsyndromal (2.1) trajectories exhibited positive ASRs and in the resistance (−3.9) trajectory exhibited a negative ASR; "pre-disaster treatment for mental illness" in the chronic (3.1), fluctuating (2.9), and recovery (2.3) trajectories exhibited a positive ASR and in the resistance (−3.6) trajectory exhibited a negative ASR.

Discussion {#sec0013}
==========

This is the first study to elucidate the trajectories of PTSD symptoms among local municipalities and hospital medical workers who responded to a large-scale natural disaster. These trajectories were subsequently classified into five groups. The majority of workers, i.e., those who followed a resistant (63%) or subsyndromal trajectory (24%) exhibited minimal to mild symptoms and remained stable throughout the study period \[i.e., 14 months (wave 1), 30 months (wave 2), 43 months (wave 3), and 54 months (wave 4) after the GEJE\]. Initially, 6% of workers showed severe (PCL-S ≥ 44) symptoms indicating probable PTSD ([@bib0005]) but recovered in the subsequent period (recovery trajectory), 3% experienced persistent severe PTSD symptoms (chronic trajectory), and 4% followed a fluctuating chronic course with ranges of moderate to severe symptoms (fluctuating trajectory). However, because our study lacked data for the period immediately after the disaster or the first year after the disaster, names of the trajectories are based on patterns observed during the study period (14--54 months after the GEJE) and careful interpretation is therefore necessary. For example, participants whose trajectory was classified as "resistance" may not have been resilient immediately after the disaster.

In accordance with previous studies ([@bib0014]; [@bib0047]; [@bib0064]), our work revealed diversity in the courses of PTSD symptoms experienced by local disaster recovery workers who responded to the major disaster. Furthermore, the trajectories observed in this study---the majority of participants were resistant or subsyndromal throughout the study period; some participants had chronic symptoms; and some showed recovery over time---are similar to those in people after other types of traumatic events, such as military personnel ([@bib0048]), survivors of the severe acute respiratory syndrome (SARS) epidemic ([@bib0007]), and cancer survivors ([@bib0031]). However, the trajectory pattern differed in several ways from the four typical trajectory patterns (i.e., resilience, recovery, chronicity, and delayed onset) described by Galatzer-Levy et al. ([@bib0016]). First, our trajectory lacked a delayed onset pattern and instead showed a fluctuating pattern. This difference may be because of variations in the duration of the study periods and characteristics of the study samples. Approximately a third of the studies included in a review by Galatzer-Levy et al. were conducted over a period of several months to 2 years, periods that were much shorter than that in our study. We speculate that if our study had been completed at 30 months after the GEJE (i.e., at Wave 2), most of the participants with fluctuating patterns in our study might have been regarded as demonstrating delayed onset pattern. Another possibility is potential selection bias resulting from the limited number of participants completing all of the waves. When we analyzed the data of the participants who completed the assessments of all four waves, the trajectory pattern was different from that of the participants who completed the assessments of the first wave and any of the following three waves. We present the trajectory of the participants who completed all four waves in Supplementary Figure 1 as well as fit information and comparison of demographics in Supplementary Tables 3 and 4. In this trajectory, "Trajectory 1" resembles the delayed onset pattern.

Another difference observed was the shape of the chronic trajectory of this study, which showed a small amount of recovery above the threshold level of probable PTSD between waves 1 and 2. We speculate that this small recovery may have been due to the characteristics of our participants, who were workers that were able to keep working from the onset of the disaster and for more than several years, so it is that the workers who were deteriorating or maintaining a greater degree of symptoms could not participate in the survey because of resignation or taking temporary leave.

Similarly, to the present analysis, studies of the events surrounding the WTC disaster examined the trajectories of PTSD symptoms for disaster recovery workers. However, the present study differs from those on the WTC in several ways, including the type of disaster, characteristics of the participants, and duration of the follow-up period. Our study targeted non-traditional disaster workers including local government employee and medical workers who continued their involvement in recovery work following the GEJE for 5 years, whereas the WTC studies elucidated the trajectories of first responders (i.e., police) and non-traditional responders (e.g., reconstruction workers) who responded to the terrorist attack and were followed up for 8 -- 12 years ([@bib0014]; [@bib0047]; [@bib0064]).

In spite of above-mentioned differences, some similarities in the patterns of progression for PTSD symptoms determined in this and the WTC studies existed. The majority of participants remained stable and showed resistance throughout the study period; a group of participants continued to experience chronic severe symptoms; and some workers exhibited delays in the deterioration or recovery of their symptoms. These patterns seem to be consistent with common post-traumatic stress reaction pathways ([@bib0016]; [@bib0046]) for survivors and workers affected by large-scale traumatic events.

However, up to 20% -- 30% of non-traditional workers who were involved in the WTC disaster showed chronic or delayed courses of deterioration ([@bib0014]; [@bib0047]) compared with 7% of the subjects identified in this study who followed chronic or fluctuating trajectories. This might be partially explained by the difference in the type of disaster. The risk of PTSD is reportedly higher following disasters caused by humans or technology, such as terror attacks ([@bib0018]), and the risk of delayed deterioration is higher after intentional ([@bib0051]) rather than natural disasters. Additionally, preparedness for a disaster, which usually reduces the risk of PTSD ([@bib0045]), may have been relatively higher among people in the coastal area of Miyagi prefecture, because the areas were repeatedly subjected to tsunamis at intervals of several decades ([@bib0052]). Past experience of tsunamis may have served as a buffer and lessened the impact of the GEJE ([@bib0045]).

Cultural ([@bib0032]) and race/ethnic ([@bib0049]) differences may have moderated the effects on mental health following the traumatic events and altered the trajectory of the PTSD symptoms. The relative low prevalence of probable PTSD observed in this study coincides with that reported in previous reports targeting survivors and the disaster responders of the GEJE ([@bib0034]). This trend may partly stem from the attitudes or mentality of Japanese people when confronted with extreme adversity, such as "gaman" (patiently persevering in tough times, absorbing losses, and maintaining internal control) and "shouganai" (the belief that the problem cannot be helped) ([@bib0019]). International media remarked on the self-restraint of Japanese people in the immediate aftermath of the GEJE: instead of chaos, such as theft or lootings, people calmly waited in line for water and food ([@bib0020]). However, many of these survivors may have expressed traumatic stress in the form of somatic or behavioral symptoms rather than in the form of emotional symptoms associated with PTSD ([@bib0019]). Because this issue was beyond the scope of our study, a wide variety of trauma-related symptoms must be surveyed to elucidate the cultural and race/ethnic differences in response to a large-scale disaster. An alternative speculation is that a lesson that has been passed down in the coastal areas devastated by GEJE exists,"tsunami tendenko" (escape from tsunami by yourself), which calls for a quick evacuation from a tsunami to higher ground without waiting for others. This inherited lesson shared by community members may have fostered mutual trust in advance and reduced feelings of self-reproach after the tsunami disaster ([@bib0066]).

Because the number of participants classified into the chronic or fluctuating trajectory was relatively small in this study, the analysis of relationships between personal and workplace factors to each trajectory were limited, and they should be interpreted carefully. Overall, compared to the participants who followed a resistant trajectory, those who followed trajectories with more severe PTSD symptoms exhibited more workplace risk factors including disaster-related work, lack of communication, or lack of rest, as well as personal risk factors directly associated with the disaster including displacement, loss of family or near-death experience, and pre-disaster treatment for physical or mental illness. These findings imply that multiple disaster-related workplace and personal stressors or pre-disaster risk factors may affect the trajectories of PTSD symptoms for local disaster recovery workers. The relationships among risk factors and higher symptom trajectories (i.e., chronic and fluctuating) have not been straightforward; for example, "pre-disaster treatment for mental illness" was related not only to the chronic and fluctuating trajectories but also to the recovery trajectory; "mainly disaster-related work" was related to the subsyndromal and recovery trajectories but not with the chronic and fluctuating trajectories. These seemingly inconsistent findings may stem from a lack of statistical power because of the small sample size. Future studies using larger samples will be necessary to elucidate the factors related to chronic or delayed dysfunctional trajectories, as well as those associated with resistance or recovery trajectories. The cross-sectional interaction of these factors and their longitudinal effects also need to be investigated. Sustained monitoring of risk factors from ordinary times and health surveys at fixed intervals post-disaster must be incorporated as psychological intervention policy for local disaster workers.

Our findings showed that both workplace and personal factors affected longitudinal PTSD symptoms, which may result in several significant implications. These findings indicate the importance of both improving overall working conditions and providing individual support for workers with higher exposure to risk factors related to disaster. Continuation of increased amount of work from immediately after a disaster may prevent maintenance of workers' mental/physical health or recovery from personal losses they suffered. Intervention targeting these workers may include measures to encourage taking adequate rest and maintaining interpersonal communications with colleagues (e.g., developing educational programs or leaflets to inform workers of the psychological response after a disaster and stress management techniques as well as to educate supervisory employees about the importance of controlling the disaster-related workload or staff rotation to prevent burn-out) ([@bib0056]). The importance of rest and good relationships with coworkers has been reported by local government officials responding to the Sichuan earthquake in China in 2008 as well ([@bib0062]).

Although Japan is frequently confronted with major natural disasters such as earthquakes, typhoons, and volcanic eruptions almost every year, relatively few studies concerning PTSD exist, and to the best of our knowledge, this is the first study to investigate trajectories of PTSD symptoms among Japanese disaster recovery workers. Previous studies reported relatively low PTSD prevalences ([@bib0034]) of 0% ([@bib0015]), 3% ([@bib0050]), and 16% ([@bib0027]) among first responders and of 0% ([@bib0057]) and 9% ([@bib0028]) in direct victims, which is much lower than the prevalences reported from Western countries, which range from 10% -- 20% among first responders and 30% -- 40% among direct victims ([@bib0018]). However, in the case of the Fukushima nuclear disasters (nuclear power plant explosion and a nuclear meltdown that occurred at the Fukushima Daiichi nuclear powerplant, triggered by the tsunami following the GEJE), 30% of workers responding to the Fukushima Daiichi nuclear powerplant ([@bib0054]) and 22% of municipality workers in the town of Fukushima [@bib68], from which all of the residents were temporally forced to evacuate, were considered as exhibiting probable PTSD. Overall, the percentage of probable PTSD (PCL-S ≥ 44) in our study was relatively lower than that of WTC workers and workers responding to the Fukushima nuclear disasters. However, the rates of probable PTSD remained persistent throughout waves 2, 3, and 4 (4.6%, 4.8%, and 5.3%, respectively), and further, 7% of the participants were classified into the chronic and fluctuating trajectories. Since the 12-month prevalence of PTSD in Japan in ordinary times is lower at 0.5% ([@bib0029]), it is important that mental health professionals and policy makers understand the persistence of the elevated risk of PTSD among local workers responding to major natural disasters over a prolonged period.

Limitations {#sec0014}
===========

Several limitations must be noted. First, there may have been a potential selection bias because the number of participants who participated in all of the surveys was small (n = 274, 29.2% of the participants at wave 1). Second, the participants in this study were limited to one region of the extensive disaster area, and participants included in the analysis were required to answer a survey at least twice. Therefore, generalizability to other workers who responded to the GEJE might be limited. Third, we used self-administered questionnaires to measure PTSD symptoms and did not conduct a psychiatric diagnostic interview to confirm the results of the questionnaires. A future study should consider using a clinician-administered structured interview. Fourth, the psychiatric consequence of disaster are not limited to PTSD symptoms and may be expressed as other symptoms such as depression, anxiety, substance abuse, and various physical disorders ([@bib0065]). Overall psychiatric and physical evaluations are necessary when providing care to disaster workers. Fifth, because our study to elucidate the factors related to a chronic or dysfunctional trajectory was relatively small, future studies should prospectively evaluate factors affecting mental health consequences, including past traumatic experiences or stressful life events prior to the survey, in a larger number of participants. Sixth, although post-disaster data on working conditions (i.e., lack of rest and lack of communication) were evaluated dichotomously ("yes"/"no"), quantitative analysis such as comparison of pre-disaster and post-disaster working hours could have elucidated more precisely how working conditions changed after the disaster. At the workplaces of disaster responders, sustained monitoring during ordinary times may help clinicians detect risk factors longitudinally and enable rapid psychological intervention for those at risk. Seventh, our first survey was conducted 14 months after the GEJE, which limited identification of the first year trajectories. The GEJE was so powerful that more than 5,000 aftershocks occurred in the following year, and local government and disaster base hospitals of the affected areas were overwhelmed by their duties; therefore, health surveys of the workers were considered to be a low priority, so we were not able to conduct the survey in the first year.

Conclusion {#sec0015}
==========

This study elucidated the diversity in progression of PTSD symptoms among local disaster recovery workers who responded to the GEJE. Although the majority of workers remained stable throughout the study period and showed minimal to mild symptoms, there were several groups of workers who exhibited severe, chronic, and/or fluctuating symptoms. These trajectories for PTSD symptoms seem to be related to multifaceted factors including the effects of workplace and personal experiences associated with the disaster. Our participants, who played dual roles as disaster survivors and support providers, confronted a diverse range of stressors over an extended period of time following the disaster. Because continuous disaster-related and life stressors following disasters are known to influence mental health conditions and functional outcomes ([@bib0009]; [@bib0017]), the multifactorial nature of disaster-based stress must be considered in order to provide care for people experiencing work-related stress or personal experience of a disaster. Future studies are necessary to develop measures to improve mental health care for local workers over a prolonged period.

Author contributions {#sec0016}
====================

AS, IU, WS, HM, KM concept and designed the study. AS, IU, KM collected data. AS and KM performed the statistical analysis. AS and KM drafted the manuscript. All authors contributed in interpretation of the data and revision of the manuscript. All authors read and approved the final manuscript.**Figure legends**

Competing Delcaration of Interest
=================================

The authors declare no conflict of interest.

Appendix. Supplementary materials {#sec0018}
=================================

Image, application 1 Image, application 2 Image, application 3 Image, application 4 Image, application 5

The authors wish to express deepest condolences to the victims of this disaster, and thank all the participants, the staff at each workplace, and the staff at the Miyagi Disaster Mental Health Care Center. The authors would also like to thank Dr. Yuriko Suzuki of the National Center of Neurology and Psychiatry for the advice on the study design and the use of PCL-S. This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Health, Labour and Welfare (H24-seishin-ippan-002-hukkou) and JSPS KAKENHI (grant number JP17K19786).

Supplementary material associated with this article can be found, in the online version, at [doi:10.1016/j.jad.2020.05.152](https://doi.org/10.1016/j.jad.2020.05.152){#interref0001}.

[^1]: Notes. PTSD, post-traumatic stress disorder; PCL-S, PTSD checklist-specific version.

[^2]: Total score of PCL-S ranges from 17 to 85. A cutoff score was set at ≥44 to indicate probable PTSD.

[^3]: Data missing for five participants

[^4]: Data missing for one participant

[^5]: Data missing for four participants

[^6]: Data missing for one participant

[^7]: Data missing for three participants

[^8]: Notes. AIC, Akaike information criterion; BIC, Bayesian information criterion; SSA-BIC, sample-size adjusted BIC; Estimated log Bayes factor = 2 × \[(SSA-BIC of the current model) -- (SSA-BIC of the previous model)\], values greater than 10 are interpreted as very strong evidence for a better fit; Entropy = average of the posterior group membership; Groups 1 to 6 shows the n (%) values of the participants assigned to each group according to the highest posterior group membership.

[^9]: Notes. PTSD, post-traumatic stress disorder; PCL-S, PTSD checklist-specific version. Total score of PCL-S ranges from 17 to 85; ASR, adjusted standardized residual, pos-hoc comparison for χ^2^ test, values greater or lesser than ±2.0 are considered to be significantly higher or lower than chance.

[^10]: Workplace factors were assessed at Wave 1 (14months), except for Pre-disaster treatment for physical illness and Pre-disaster treatment for mental illness which were collected at Wave 2 (30 months) and 3 (43months).

[^11]: Mainly disaster-related work in the subsyndromal (3.0), and recovery (3.3) trajectories had positive ASRs, indicating that the participants included in the subsyndromal and recovery trajectories had factors significantly greater than chance. The resistance trajectory (−5.3) had a negative ASR, indicating that the participants included in the resistance trajectory had factors significantly less than chance.

[^12]: Lack of communication in the chronic (2.1), fluctuating (3.3), and recovery (2.1) trajectories had a positive ASR and in the resistance (−4.6) trajectory negative ASR.

[^13]: Lack of rest in the chronic (3.8), recovery (3.2) and subsyndromal (2.8) had positive ASRs and in the resistance (−5.8) trajectory had a negative ASR.

[^14]: Displacement in the chronic (3.1) trajectory had a positive ASR and in the resistance (−2.8) trajectory had a negative ASR.

[^15]: Dead or missing family members in the chronic (3.0) trajectory had a positive ASR and in the resistance (−2.0) trajectory had a negative ASR.

[^16]: Near-death experience in the chronic (2.4) and recovery (3.1) trajectories had positive ASRs and in the resistance (−4.5) trajectory had a negative ASR.

[^17]: Pre-disaster treatment for physical illness in the chronic (4.3) and subsyndromal (2.1) trajectories had positive ASRs and in the resistance (−3.9) trajectory had a negative ASR.

[^18]: Pre-disaster treatment for mental illness in the chronic (3.1), fluctuating (2.9), and recovery (2.3) trajectories had positive ASRs and in the resistance (−3.6) trajectory had a negative ASR.

[^19]: All the groups were significantly different (Bonferroni correction, p \< 0.05/10 = 0.005).

[^20]: All the groups were significantly different, except those for chronic and fluctuating (Bonferroni correction, p \< 0.05/10 = 0.005).

[^21]: All the groups were significantly different (Bonferroni correction, p \< 0.05/10 = 0.005).

[^22]: All the groups were significantly different, except those for chronic and fluctuating and for recovery and subsyndromal (Bonferroni correction, p \< 0.05/10 = 0.005).
