Epidemiological study of sarin poisoning in Matsumoto City, Japan.

On the night of June 27, 1994, about 12 liters of sarin were released by terrorists in Matsumoto City, Japan. In order to investigate the epidemic, community-based questionnaire surveys were conducted. The subjects were all inhabitants (2052 people) living and staying in an area of 1050 meters from north to south and 850 meters from east to west including the sarin release site. Participants included 1743 people who answered the questionnaire at the first survey; those with symptoms were contacted for follow-up at four months and one year after the episode. The number of sarin victims were 471 persons. Muscarinic signs were common to all victims; nicotinic signs were only seen in severely affected victims. The geographical distribution of sarin victims was closely related to the direction of the wind. Three weeks after the intoxication, 129 victims still had some symptoms such as dysesthesia of the extremities. At that time, many victims had begun to experience asthenopia, which was even more frequent at four months. Although victims who felt sarin-related symptoms had decreased by a year, some still had symptoms such as asthenopia. Sarin released in a suburban area affected approximately 500 inhabitants living nearby; some still had symptoms a year after the intoxication.

On the night of June 27, 1994, about 12 liters of sarin were released by terrorists in Matsumoto City, Japan. In order to investigate the epidemic, community-based questionnaire surveys were conducted.
The subjects were all inhabitants (2052 people) living and staying in an area of 1050 meters from north to south and 850 meters from east to west including the sarin release site. Participants included 1743 people who answered the questionnaire at the first survey; those with symptoms were contacted for follow-up at four months and one year after the episode.
The number of sarin victims were 471 persons. Muscarinic signs were common to all victims; nicotinic signs were only seen in severely affected victims. The geographical distribution of sarin victims was closely related to the direction of the wind. Three weeks after the intoxication, 129 victims still had some symptoms such as dysesthesia of the extremities. At that time, many victims had begun to experience asthenopia, which was even more frequent at four months. Although victims who felt sarin-related symptoms had decreased by a year, some still had symptoms such as asthenopia.
Sarin released in a suburban area affected approximately 500 inhabitants living nearby; some still had symptoms a year after the intoxication. J Epidemiol, 1998; 8 : 33-41.
sarin, mass poisoning, symptoms Sarin (isopropyl methylphosphonofluoridate), an organophosphate nerve agent, is highly toxic and is considered to be a lethal chemical warfare agent. When dispersed as a vapor, it is readily absorbed through the respiratory tract or any body surface1). The intoxicating manifestations of exposure include all those that can be expected from the inhibition of acetylcholinesterase (AChE) resulting in acetylcholine excess 2).
Hitherto, many sarin exposure experiments have been conducted using laboratory animals [3][4][5][6][7][8]. A few human cases of sarin poisoning have also been reported; these were military accidents 9,10) or experimentally investigated sarin miosis using volunteers11, 12). There is no report of mass poisoning with sarin in a suburban area. On the night of June 27, 1994, about 12 liters of sarin were released by terrorists using a heater and fan in Matsumoto City, Japan (according to a police office report), causing harm to many inhabitants in the surrounding areas, including seven deaths (five men, and two women). The identification of the toxic vapor was made from air or water samples collected near the sarin release site by gas chromatograph-mass spectrometer at the Nagano Research Institute for Health and Pollution 13) A second attack with sarin vapor later occurred in the Tokyo subway on March 20, 1995 14,15).
In order to clarify the details of the epidemic of the sarin poisoning in Matsumoto, we surveyed inhabitants of the area where the sarin was released. We determined the time of onset, geographic location, and evolution of symptoms in those affected by the exposure.

MATERIALS AND METHODS
Condition of release of toxic substance Twelve liters of sarin were released by terrorists using a heater and fan from a truck between 22:40 and 22:50 on 27th, June, 1994 (according to a police office report). The weather at that time was rainy at 20.51C with a 0.6-1.7 meter per second wind from the southwest and 93 % humidity.

Subjects
In order to clarify the characteristics of sarin victims and the observed effects, three questionnaire surveys were conducted by the Health Research Subcommittee of the Medical Committee for the Toxic Gas Intoxication of the Matsumoto City Regional Comprehensive Medical Council. In each survey, informed consent was obtained from all subjects: the purpose of the survey was also included in the questionnaire. In a preliminary survey by interview, we confirmed that the sarin victims were distributed within an area of 1050 meters from south to north and 850 meters from east to west, consisting of nine town districts. The subjects of this study were all inhabitants (2052 people) who lived or stayed in the area, between the 27th and 28th of June, 1994 in Matsumoto City, Japan. In Japan, the addresses of all the inhabitants are registered at the regional office. As the district was a residential areas and there were no hotels or lodging facilities, it was estimated that there were no or very small number of victims, if any, who were excluded from this study. All inhabitants in Japan can consult doctors using medical insurance with minimal or free of charge.

The first survey
The first survey was conducted three weeks after the deliberate release of sarin. The questionnaire consisted of five items as follows: questions about personal information such as name, age, sex and address; 23 questions on symptoms (sneezing, rhinorrhea, nasal voice, sore throat, coughing, dyspnea , darkness of visual field, narrowing of visual field, flickering of vision, ocular pain, increase of lacrimation, blurriness of vision, diplopia, headache, nausea, vomiting, dizziness, dysesthesia of the extremities, muscle cramp, gait disturbance, paresis of perioral muscle, dysphagia and fatigue) that subjects experienced immediately after sarin intoxication and those remaining three weeks after the intoxication; questions regarding hospitalizaions and consultations with doctors; questions about when and where they experienced the symptoms; and questions concerni ng their location in their house and whether windows were o pen. The questionnaire was distributed to all subjects and recovered by the leader of each town district according to the notification of Matsumoto City Office. The questions were completed by the inhabitants at their homes. When subjects could not answer by themselves (e.g. infants), the questions were answered by another member of the family. The recovery of the questionnaire was 84.9 percent (1743 subjects, 847 men, 877 women and 19 sex non-specified), and the addresses of these respondents were registered.

The Second Survey
Four months after the release of sarin, we conducted a second survey of the health status of those victims who still had symptoms associated with the vapor three weeks after the episode (129 persons). The questionnaire consisted of only two sections: questions about personal information; 23 questions as shown in the first survey plus 8 additional questions (insomnia, difficulty in reading and writing, asthenopia, palpitation, shoulder stiffness, feeling of heaviness in the head, husky voice and slight fever). These additional items were those complained of by sarin victims at three weeks after the episode. The questionnaires were sent to the victims and returned by mail; 105 people (18 people of the group hospitalized, 61 who consulted doctors, and 26 who did not) responded (81.4 percent of the injured victims who had subjective symptoms at three weeks) .

The third survey
A year after the deliberate release of sarin, we again surveyed all victims (45 persons) who had reported symptoms four months after the episode. The questionnaire consisted of two sections: questions about personal information such as name, age, sex and address; 13 questions on symptoms (headache, fatigue, feeling of heaviness in the head, insomnia, shoulder stiffness, asthenopia, difficulty in reading and writing, blurriness of vision, husky voice, slight fever , palpitation, difficulty smoking and having bad dreams), which were constructed according to those reported at the second survey. The questionnaires were sent to the victims and returned by mail; all the people responded.
Along with the three surveys, health checks and laboratory examinations including erythrocyte AChE activity were encouraged without charge at four weeks after the episode for inhabitants who lived in the setting area; for inhabitants who showed lowered erythrocyte AChE activity at this time , the measurement was followed up until four months after the episode. The results were described elsewhere 16,'

Statistical analysis
All of the data were analyzed at the Department of Hygiene , Shinshu University School of Medicine using the SPSS-X (SPSS Inc, Chicago) program on Hitachi (Tokyo) HITAC M240H at the Computer Center of Shinshu University . The victims were divided into three groups according to their after exposure to sarin and the recovery b, Additional symptoms reported by some, but not included in the questionnaire Symptoms excluded in the questionnaire * ** *** , Significant differences were noted between the groups hospitalized and those who consulted doctors, or between groups who consulted doctors and those who did not at p<0.05. P<0.01 and p<0.001, respectively .
where satin was released (min Fig 2), 76 % of all inhabitants experienced some symptoms. All of the seven persons who died, and 68 % of the hospitalized victims were also in this same block.
The majority (80 %) of all victims were located in an elliptical area (within the shadow in Fig 2) with a 400 meter long axis north east of the site. Other victims were distributed outside of the elliptical area, but all of them experienced only min-imal symptoms not requiring medical consultation.
All satin victims were located in an area estimated to be 800 meters from south to north and 570 meters from west to east. A satin victim who consulted a doctor was located at an area 500 meters west of the site where satin was released.
The places where victims were exposed to satin were also investigated in the first questionnaire survey. Over 80 % of the victims were exposed inside of their houses, and of these vic-  after the sarin intoxication.

DISCUSSION
From our survey, the prevalence of satin poisoning was estimated to be 27.0 %. At the time when the sarin was released, it was rainy with a 0.6-1.7 meter per second wind from the southwest in the area. The majority of the victims were concentrated in an elliptical area with a 400 meter long axis north east from the site where the sarin was released, suggesting that the geographical distribution was closely related to the wind direction. Within the elliptical area, the air in the block where the sarin was released was severely polluted as shown by the large number of victims who died or were hospitalized.
It is interesting that the onset of the symptoms attributable to sarin occurred with two peaks in number during the first 12 hours. The first peak was immediately after the sarin was released; this group had a high percentage of severely affected victims. The second peak appeared 8 hours later, after many inhabitants began to leave their homes in the morning; this group predominantly experienced mild symptoms. The victims in the second peak were situated both inside and outside of the highly polluted elliptical area (in Fig 2), suggesting that low levels of sarin vapor inducing mild intoxication still occurred both near the release site and polluted areas wider than the area with immediate intoxication. Indeed, samples taken at 11:00 in the morning found sarin in the air inside of the nearest house north of the release site, and also in the water samples from a pond outside's). Since most people were sleeping between 24:00 and 6:00, those with symptoms might be simply small extremities. In rodents, sarin is thought not to cause neuropathy except after sublethal repeated exposure22-24). Our data showing that dysesthesia in the extremities was most prominent at three weeks suggests that sarin has an effect on the peripheral nervous system. However, this symptom was not seen four months after intoxication, and none of these victims showed any abnormality in nerve conduction studies (data not shown). The complaint of asthenopia occurred in victims with lowered erythrocyte AChE activity at three weeks after the intoxication. It is noteworthy that the frequency of this complaint further increased at four months after the intoxication and was still present after one year, although erythrocyte AChE activity returned to normal in all victims studied (data not shown). In addition, among victims still having symptoms a year after the intoxication, more than 50 % felt symptoms such as fatigue, asthenia, and blurriness of vision, and 40 % felt shoulder stiffness. The severer the symptoms sarin victims experienced after the sarin intoxication, the greater the symptoms they retained. The mean age of these victims was not different from those whose symptoms had resolved, suggesting that further followup study including people without symptoms should be done to evaluate whether the symptoms reported a year after the intoxication are a later sequelae of acute exposure to sarin. Since some victims requiring hospitalization still had bad dreams, slight fever and symptoms of palpitation, these should also be followed.
In the present survey, people whose symptoms were solved at early stage were not included afterward. Therefore, the numbers of people who had symptoms four months and a year after sarin incident might be estimated low. Although the validity of results might be pointed because of the nature of questionnaire, that was partially covered by the measurement of AChE activity.