Participants were recruited from among the DMAT members deployed to the disaster area between March 11 and 22, 2011 following the earthquake. DMAT members are physicians, nurses, and operational coordination staff (medical or clerical staff who are neither physicians nor nurses) who are dispatched as a specially trained mobile medical team to conduct emergency medical relief activities during the acute phase of a large-scale disaster and in the event there are large numbers of injured or sick casualties. The inclusion criteria were 1) aged 18 years or older, 2) a native Japanese speaker or non-native speaker with Japanese conversational abilities, and 3) physically and psychologically capable of understanding and providing consent for study participation.
This study was conducted as part of the clinical trial “Attenuating posttraumatic distress with omega-3 polyunsaturated fatty acids among disaster medical assistance team members after the Great East Japan Earthquake”. The detailed study procedures have been reported elsewhere . Briefly, a written guide to the study was posted by the DMAT Office on the Emergency Medical Information System website, and affiliated hospitals with DMAT members were notified of the posting by their local municipalities. Survey packets were then mailed on April 2 to all DMAT members who had been deployed to the disaster area. Those willing to participate signed and returned the enclosed consent form by mail or fax to the DMAT Office by the closing date of April 12.
Participants were surveyed using a self-report questionnaire that we prepared and operationalized the question in a binary (yes/no) way for this study. They provided information on the following items, in addition to those variables identified as risk factors for PTSD in previous research [3, 4]: past history of psychiatric illness, period of deployment, stress prior to deployment, injury during deployment, experience of saving a child during deployment, experience of contact with corpses, concern over radiation exposure, and duration of time spent watching earthquake news reports. To evaluate past history of psychiatric illness, participants answered the question, “Have you ever received any treatment for your mental health problem?”. To evaluate stress prior to deployment, participants answered the question, “Did you feel stressed just prior to deployment?”. To evaluate concern over radiation exposure, participants answered the question, “Were you concerned over radiation exposure during the deployment?”. In regard to alcohol drinking, we prepared the following question “Do you drink alcohol?” and the answers “I have never drank”, “I currently refrain from drinking” and “I drink”. We defined “current drinker” as those respondents that chose the third answer “I drink”.
To evaluate psychological distress, respondents completed the Kessler 6 (K6) scale [5, 6], the Center for Epidemiologic Studies Depression Scale (CES-D) [7, 8], the Peritraumatic Distress Inventory (PDI) [9, 10], and the Impact of Event Scale-Revised (IES-R) [11, 12]. The K6 was designated to screen psychiatric disorders and mood and anxiety disorders. An adequate cutoff score on the K6 for serious mental illness with a score of less than 60 in the global assessment of functioning is 0–12 vs. 13 or more . The cutoff score on the CES-D for depression is considered to be 16 or more . The PDI assesses quantification of fear and sense of helplessness in the period during and immediately after a traumatic experience, and the cutoff score on the PDI for subsequent PTSD is 23 or more . The IES-R evaluates PTSD symptoms and is the most widely used measure internationally in all forms of disaster-area research. Reliability and validity for each of these scales has been confirmed in the Japanese population [6, 8, 10, 12]. Cronbach’s alpha for the K6, CES-D, PDI, and IES-R in this sample was .89, .85, .83, and .94, respectively.
This study protected the rights and welfare of the participants in the spirit of ethical guidelines outlined in the Declaration of Helsinki, and further respected the ethical principles of the Ministry of Health, Labour, and Welfare of Japan. The research plan (No. 2010–32) was deliberated upon and approved by the Ethics Committee of the National Disaster Medical Center on April 1, 2011. After providing a complete description of the study, written informed consent was obtained from all participants involved in the present study.
Participants were assigned to 1 of 2 groups according to the presence or absence of concern over radiation exposure. Inter-group comparisons of the dependent variables, including K6, CES-D, PDI, and IES-R scores, were performed using an analysis of variance (ANOVA) after stratifying for sex. An analysis of covariance (ANCOVA) was then performed to examine the specific effect of concern over radiation exposure with age, occupation, disaster operation experience, duration of time spent watching earthquake news, and past history of psychiatric illness as covariates. Statistical significance was set at p < 0.05 and all statistical analysis was performed using SPSS version 17 (SPSS Inc., Tokyo, Japan).