Psychological stress of emergency medical staff after the largest mass murder incident in post‐World War II era

Abstract Background A mass‐casualty incident occurred on July 26, 2016, at Tsukui Yamayuri‐en, which is a welfare facility for people with intellectual disabilities. Nineteen residents with intellectual disabilities were killed, and 26 other residents and staff members were injured. Kitasato University Hospital Emergency and Disaster Medical Center treated many patients in serious condition at the site and in the hospital. Aims The authors investigated the symptom severity and distributions of posttraumatic stress disorder (PTSD) among the emergency medical staff in charge. The subjects of this study were the staff members, mostly working at the Emergency and Disaster Medical Center, who treated the people injured in the incident. Methods We conducted a questionnaire survey using Impact of Event Scale‐Revised (IES‐R) on 104 staff members, and 79 responded. Results The IES‐R scores of nurses were significantly higher than those of doctors. There was no significant difference in the scores between male and female staff members, and there was no correlation between the score of each IES‐R subscale and age. Conclusion Results suggest that mental care should be provided to emergency medical staff, especially nurses who treat trauma patients involved in disasters and heinous crimes.

sudden mass murder incidents and large-scale disasters may experience CIS.
It is important to consider the CIS of emergency and disaster relief workers who rescue or provide medical care to victims of large-scale disasters or mass-casualty crimes and who hold major responsibilities. They often suffer from posttraumatic stress disorder (PTSD), which continues for a long duration.
There are few reports on the stress experienced by their mental health of medical and emergency medical staff providing medical care at the scenes of large-scale disasters or mass-casualty incidents.
Investigating the level of psychological stress of emergency medical staff, however, is important for them to be able to maintain their good mental health. We investigated the stress and mental health of the medical and emergency medical staff involved in treating the victims of the above incident.

| Subjects
The subjects of this study were the staff of Kitasato University Hospital working at the Emergency and Disaster Medical Center, who treated the people injured in the murder incident that occurred at Tsukui Yamayuri-en care facility on July 26, 2016.
The center is located in Sagamihara City in the northern part of Kanagawa Prefecture, Japan, and is the only third-level emergency hospital in the city. As an emergency hospital, the center covers a total population of more than 1.5 million people. We conducted a questionnaire survey of 104 staff members, and 79(76.0%)re-

| Measures
The Japanese translated version of Impact of Event Scale-Revised (IES-R-J) was used in the survey. IES-R is a self-report questionnaire developed by Weiss and Marmar 2 for the purpose of assessing PTSD symptoms. IES-R consists of 22 items divided into three subscales, namely intrusive recollections (hereafter, intrusion), avoidance, and hyperarousal, which are three major PTSD symptoms 2,3 The subjects were asked to rate the severity of symptoms over the past week on a five-point scale (0-4) for each of the 22 items. Those with an IES-R total score of 25 or higher (0-88 points) are considered likely to develop PTSD 3,4

| Statistical analysis
Background characteristics such as gender and license type (for classifying the subjects as physicians, nurses and others) of the subject were summarized. Furthermore, age and the IES-R scores for each subscale were analyzed. Data were analyzed by tests for unmatched pairs using statistical significance tests. To compare the difference for unmatched pairs, the score of each IES-R subscale was compared between genders using the Mann-Whitney U test. The Kruskal-Wallis test was used in the comparison of the score of each IES-R subscale between license types and the Mann-Whitney U test for multiple comparisons. The relationship between the age and the score of each IES-R subscale was analyzed using Spearman's rank correlation coefficient.
For the interpretation of results, the significance probability for each analysis was corrected by the Bonferroni method as a multiple adjustment method. The statistical analyses were performed using SPSS 22.0 (IBM SPSS Inc2013).

| Background characteristics
The background characteristics of the subjects are shown in Table 1.
The total score of all IES-R subscales and the score of each IES-R subscale for genders and license types are shown in Table 3. The mean IES-R total scores for males and females were 3.4 ± 7.5 and 2.8 ± 6.7, respectively. The mean IES-R total scores for the subjects grouped by license type were 1.0 ± 2.7 for physicians, 6.0 ± 9.0 for nurses, and 3.5 ± 8.0 for others. Among them, one nurse and one person in the group with other license types were identified as highrisk individuals on the basis of their IES-R scores. In the grouping according to license type, the mean subscores for intrusion, which is a subscale of IES-R, were 0.3 ± 0.9 for physicians, 2.

| Comparison of IES-R score between genders and groups by license type
The IES-R total scores for genders and license types are shown in Table 4. There was no significant difference in the IES-R total score between males and females (Z = −0.07, P = .943). The main effect was recognized in the IES-R total score for license type (χ 2 = 7.35, P = .025), and multiple comparisons showed that the IES-R total score of nurses was significantly higher than that of physicians (Z = −2.68, P = .007). In all subscales, there was no significant difference between genders, and no main effect between groups by license type was observed. On the contrary, there was no correlation between the score of each IES-R subscale and age (Table 5).

| Psychological stress of emergency medical staff
There was no significant gender difference in the IES-R total score.
In general, the risk of developing PTSD is higher in females than in males 5,6 however, a report showed that there is no significant gender difference in the risk of developing PTSD after natural disasters and accidents and that the risk tends to be low in both males and females 7 Age is considered to be a factor affecting coping behavior. It has been suggested that the coping mechanism becomes rigid and loses its flexibility in dealing with stress with advancing age 8 In this study, however, there was no correlation between each IES-R score and age. Although young medical staff account for a high proportion of emergency medical staff, it is also important to provide mental care to older staff.
The IES-R scores of nurses were significantly higher than those  In multiple comparisons, the significance level set at two-tailed P < .017 was estimated by the Bonferroni method. Significant values are in boldface and underlined.
There was no significant difference between genders in the score of each subscale (Intrusion:

| LIMITATI ON S AND FUTURE CHALLENG E S
Care must be taken in interpreting the results of this study because it was conducted in a short period of time immediately after the Tsukui Yamayuri-en incident. Also, it should be taken into account that most of the emergency medical staff in this study provided medical care not at the site of the incident but within the facilities of the hospital.
It is necessary to examine in the future the late-onset emotional reactions to a shocking incident.

| CON CLUS IONS
The psychological stress experienced by the emergency medical staff who treated victims of the worst mass murder incident in post-World War II Japan was examined. The results suggest that providing mental care is important for the emergency medical staff, especially nurses, who treat patients in a serious condition and patients with trauma caused by disasters and crimes. The results show that care should be taken to support their mental health, especially in serious events.

ACK N OWLED G M ENT
We thank the staff of Kitasato University Hospital working at the Emergency and Disaster Medical Center.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest.

AUTH O R CO NTR I B UTI O N S
All authors contributed to data collection and analysis and revision of the manuscript. All authors have read and approved the final version.

I N FO R M E D CO N S E NT
All the subjects provided written informed consent after receiving a thorough explanation of the purpose and method of this study.

R EG I S TRY A N D TH E R EG I S TR ATI O N N O. O F TH E S TU DY/ TR I A L
Not applicable.

A N I M A L S TU D I E S
Not applicable.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data are not publicly available due to privacy and ethical restrictions. The raw data belonged to the present study cannot be made publicly available, because the disclosure of personal data was not included in the research protocol of the present study.