Sequelae of Sarin Toxicity at One and Three Years After Exposure in Matsumoto , Japan

In order to clarify the later sequelae of sarin poisoning that occurred in Matsumoto City, Japan, on June 27, 1994, a cohort study was conducted on all persons (2052 Japanese people) inhabiting an area 1050 meters from north to south and 850 meters from east to west with the sarin re lease site in the center. Respondents numbered 1237 and 836 people when surveys were conducted at one and three years after the sarin incident, respectively. Numbers of persons with symptoms of sarin toxicity were compared between sarin victims and non-victims. Of the respondents, 58 and 46 people had symptoms associated with sarin such as fatigue, asthenia, shoulder stiffness, asthenopia and blurred vision at both points of the survey, respectively. The prevalences were low; some complained of insomnia, had bad dreams, difficulty in smoking, husky voice, slight fever and palpitation. The victims who had symptoms one year after the incident had a lower erythrocyte cholinesterase activity than did those who did not have symptoms at the early stage; such persons lived in an area with a 500 meter long axis north east from the sarin release site. The three-year cohort study clearly showed that the odds ratios of almost all of the symptoms were high in the sarin-exposed group, suggesting a positive relationship between symptoms and grades of exposure to sarin. These results suggest that symptoms reported by many victims of the sarin incident are thought to be sequelae related to sarin exposure J Epidemiol, 1999 ; 9 : 337-343


Sequelae
of Sarin Toxicity at One and Three Years After Exposure in Matsumoto, Japan Tamie Nakajima 1, Setsuko Ohta 2, Yoshimitsu Fukushima 1, and Nobuo Yanagisawa 3,* In order to clarify the later sequelae of sarin poisoning that occurred in Matsumoto City, Japan, on June 27, 1994, a cohort study was conducted on all persons (2052 Japanese people) inhabiting an area 1050 meters from north to south and 850 meters from east to west with the sarin re lease site in the center.Respondents numbered 1237 and 836 people when surveys were conducted at one and three years after the sarin incident, respectively.Numbers of persons with symptoms of sarin toxicity were compared between sarin victims and non-victims.
Of the respondents, 58 and 46 people had symptoms associated with sarin such as fatigue, asthenia, shoulder stiffness, asthenopia and blurred vision at both points of the survey, respectively.
The prevalences were low; some complained of insomnia, had bad dreams, difficulty in smoking, husky voice, slight fever and palpitation.The victims who had symptoms one year after the incident had a lower erythrocyte cholinesterase activity than did those who did not have symptoms at the early stage; such persons lived in an area with a 500 meter long axis north east from the sarin release site.The three-year cohort study clearly showed that the odds ratios of almost all of the symptoms were high in the sarin-exposed group, suggesting a positive relationship between symptoms and grades of exposure to sarin.
These results suggest that symptoms reported by many victims of the sarin incident are thought to be sequelae related to sarin exposure J Epidemiol, 1999 ; 9 : 337-343 cohort study, Matsumoto sarin incident, sequelae of sarin toxicity, subjective symptoms On the night of June 27, 1994, about 12 liters of sarin were released in Matsumoto City, Japan by terrorists using a heater and fan and a remodeled truck 13).Based on our previous survey, the victims were estimated to number approximately 600 inhabitants, including seven who had died (five men, and two women) 3) In the early stage after the sarin attack, the victims had mainly muscarinic-related symptoms and some nicotinic ones, such being closely related with lowered activity of erythrocyte cholinesterase s.Almost all these symptoms disappeared within one year after the incident.However, many symptoms persisted 3).
In an attempt to clarify whether the symptoms reported one year after the sarin incident were sequelae of the single exposure to sarin, we surveyed inhnabitants living in the area where sarin had been released.We examined the relationship between the persisting symptoms and the severity endured immediately after the sarin attack.Differences in prevalence of symptoms between subjects exposed to sarin and those not so exposed were also investigated.

Background
In attempts to clarify symptoms and complaints of sarin victims, five questionnaire-related surveys (three weeks, four months, one, two and three years after the sarin incident) were conducted by us.The results from the first two surveys have been reported elsewhere 3).Health examinations were also conducted after each survey for persons who wanted to consult clinical doctors, including neneurologists, internists and ophthal-der and address, 2) whether they were given a diagnosis of satin toxicity or had muscarinic and/or nicotinic symptoms reported elsewhere3) immediately after the satin exposure, and 3) whether they felt these symptoms between a month and a year after the sarin incident, that is, whether they had delayed symptoms due to sarin exposure; for subjects who responded 'yes's to the second and the third questions , 1) questions regarding hospitalizations and consultations with doctors after the satin attack, and 2) 13 questions on symptoms felt within a recent month (Table 1), as constructed according to findings at the survey done four months after the incident.The questionnaire was distributed to all subjects and collected by the leader of each town district.When subjects moved to another place, the questionnaire was sent to the victims by mail and they were asked to return their replies by mail.In Japan, the address of inhabitants was registered in the regional administrative office so that addresses of the inhabitants who had moved elsewhere could be traced by the regional office.60.3 percent (1237 subjects, 616 men, 609 women, 12 unknown) filled out the questionnaire.

Survey at about three years after the satin exposure
To determine if symptoms reported by the victims of sarin at one year after the attack were related to satin exposure, we Table 1.Prevalence of symptoms subjectively described one year after satin exposure.
Figures and those in the parentheses represent those with some symptoms and the percentages, respectively.Another four inhabitants also complained of experiencing these symptoms but they did not report satin-related symptoms immediately after the satin incident.a Singnificant differences were noted between the group admitted and out patients b Singnificant differences were noted between the group out and non patients c Singnificant differences were noted among the group admitted, out and non patients d Sneezing , Sore throat, dysesthesia of extremities, cough, rhinorrhea,difficulty in writing and reading *p<0 .05,**p<0.01,***p<0.001asked questions of symptoms felt within a recent month (2000 persons excluding 52 rescuers) living in the area at about three years after the incident (February, 1997).Health status of the rescuers was investigated by an occupational doctor three years after the incident; no rescuer experienced symptoms associated with sarin 6).The questionnaire consisted of four sections, for all subjects: 1) questions related to name, age, gender and address; 2) whether they felt the symptoms listed in Table 1, as prepared according to findings in the survey conducted at one or two years after the incident; 3) whether they were given a diagnosis of sarin toxicity or had muscarinic and/or nicotinic symptoms immediately after the sarin incident; 4) questions regarding hospitalization and consultation with doctors after the exposure to sarin.The respondents numbered 41.8% (394 men, 429 women, 13 unknown).In this survey, people who responded 'yes' to the third question were designated as a victim group (167 people, 36.1% of the victims immediately after the incident; the mean *SD of age, 44.4* 19.8), and those who did not as the non-victim group (669 people, 54.5% of the non-victim immediately after the incident; 54.2 * 21.5).Of the victims, 27 people (67.5% of the diagnosed victims immediately after the incident) were hospitalized, 109 (69.9%) consulted doctors, and 31 (11.3%) did not consult a doctor immediately after the poisoning.
Along these two surveys as well as another two (surveys at three weeks and two years after the sarin incident), free health checks and laboratory examinations were encouraged following the questionnaire surveys on inhabitants who lived in the area exposed to sarin.In the health check after the first survey, 152 people were admitted, and in the health check after one and three years' surveys, 72 and 31 were admitted, respectively.The results were described elsewhere4) Of the those admitted in the survey at one year after the sarin incident, 93 were admitted for a first health examination and erythrocyte (R-AchE ) and serum acetyl cholinesterase (S-AChE-) activity were measured.

Statistical analysis
All of the data were analyzed using the SPSS-X (SPSS Inc , Chicago) program on HITAC M240H (Hitachi, Tokyo).To determine the severity of the sarin intoxication, the victims were grouped into three based on findings in the survey at one year: the victims requiring hospitalization (admitted patient group); the victims who consulted doctors but did not require hospitalization (outpatient group); and others who had symptoms but did not consult a doctor (non-patient group).There were significant differences in the mean number of symptoms immediately after sarin exposure among the three groups3).The significance of the prevalence of symptoms reported one year after sarin exposure among the medical consultations was tested by the chi-square test.The difference in R-and S-AchE activity at an early stage of intoxication between people who had and did not have symptoms at a year was tested by Oneway ANOVA.In the survey after three years, differences in the prevalence of symptoms between two groups (victim and nonvictim groups), and that of people who had and did not have each symptom during the surveys were evaluated by chisquare test.In all cases using the chi-square test, Fisher's exact test was introduced if the number in one group was too small.The odds ratio of symptoms in the victim group was also calculated before and after standardizes age.

RESULTS
Of the subjects who filled out the questionnaires (1237) , sa rin victims were 318 people, and non-victims were 919 people.Of the victims, 58 (28 men, 30 women) reported symptoms associated with sarin at one year after the exposure (Table 1).The mean age of these symptomatic victims was 45.9 * 19.0, the same as that (48.5 * 20.1) of those with resolved symptoms (260 people).No difference was seen in these subjects with regards to the effects and gender.Of these subjects, 11 people were admitted as patients, at the acute stages, 26 were outpatients, and 17 people were non-patients.The remaining four victims did not state their medication after sarin exposure.There were significant differences in the percentage of symptomatic subjects among admitted patients (27.5% of those immediately after the sarin incident 4), outpatients (16.7%) and non-patients (6.2%) one year after the sarin incident (p<0.05).
The most prominent symptoms reported were asthenopia, followed by fatigue, blurred vision, asthenia and shoulder stiffness.Some victims complained of insomnia, husky voice, bad dreams, palpitations, narrowing of visual field, difficulty in smoking and slight fever, albeit the frequency in victim number being low.
Of the admitted patient group, all subjects experienced fatigue and asthenopia, more than 60% asthenia and blurred vision.These symptoms were also stated by many outpatients and non-patients.Complaints of having bad dreams, difficulty in smoking, slight fever and palpitations were not complained of by subjects who did not consult a doctor .Severity-dependent difference was noted in the percentage of symptom of fatigue.Significant differences in the percentages of symptoms of blurred vision and difficulty in smoking were seen between admitted and outpatient groups, but not between outpatient and non-patient groups.
Table 2 shows E-and S-AChE activity at the early stage for victims who had and did not have symptoms one year after the sarin exposure.No differences were seen in S-AChE activity between those with and without each symptom .The activity in people who had some symptoms one year after was significantly lower than those who did not.E-AChE activity of those who felt fatigue, asthenia and asthenopia was significantly aFigures represent numbers of subjects who had (yes) and did not have (no) symptoms.bF igures represent the mean±SD, or the value when the numbers were under three.* , **, ***Significant differences were noted between subjects who had and did not have symptoms at 0.05, 0.01 and 0.001, respectively.lower than those who did not.Because the number of symptoms was low, and comparisons were not feasible, the E-AChE activity in all victims who had difficulty in smoking and two of three people who had a slight fever was low (0.5 U).There were no differences in the mean age of the people who had and did not have each symptom.
Locations of subjects who had some symptoms one year after sarin exposure were mapped by postal code, and percentages of the symptomatic subjects in each block were calculated (Fig 1).The percentage was greatest in the block where sarin was deliberately released, followed by the blocks north and north east.Almost all these victims were located in an elliptical area (within the shadow in Fig 1 ) with a 400 meter long axis north east of the site.
Table 3 shows differences in percentages of symptoms between non-victim and victims, and the odds ratios at three years after the sarin incident.The percentage of victims with one or more symptoms was 27.5% (21 men and 25 women), which was significantly higher than that of non-victim (5.4%, 36 people); gender and age differences were nil.Of the victims with some symptoms (46 people) three years after the incident, 40 (87%) complained of asthenopia, and 25 (54.3%),18 (39.1%),15 (32.6%), 14 (30.4%)complained of fatigue, blurred vision, shoulder stiffness and asthnia or headache, respectively.The percentage of these symptoms was significantly greater in the victims than in the non-victims.The percentage of victims having slight fever was also greater in the former than in the latter.In agreement with these findings, the odds ratios of these symptoms, given exposure to sarin, were also greater.No differences were noted in the symptoms of those with bad dreams, insomnia, narrowing of the visual field, difficulty in smoking, husky voice and palpitation between  Figures and those in the parentheses represent numbers who had symptoms and the percentages, respectively non-victims and victims.Odds ratios for each symptoms after standardized age did not differ from those mentioned above (data not shown).
The prevalence of victims with symptoms both one and three years after satin incident (Victims A in Table 3) was also compared to those of non-victims.Significant differences were seen in the prevalence of symptomatic subjects or those with the symptoms of blurred vision and asthenopia etween victims A and non-victims.Odds ratios for symptomatic victims or victims with blurred vision and asthenopia were also greater in the victims than in non-victims.

DISCUSSION
There had been little or no information about later sequelae of acute satin exposure to citizens in a residential area.As a report for late sequelae of satin intoxication, only one person accidentally exposed to satin was followed up to 6 months; temporary effects of depression, fatigue, insomnia, irritability, nervousness, and impairment of memory were experienced and he died suddenly 18 months after the exposure following acute myocardial infarction.Subtle central nervous system effects are often present four weeks after the exposure, but complete recovery usually occurs unless severe anoxia has caused residual brain damage *.
In studies on the Matsumoto satin attack, we could not set controls; subjects who did not feel sarin-related symptoms were designated as non-victims, and used as internal controls in the survey at three years after the incident.In addition, background prevalence of the sarin-related symptoms was unclear.Nevertheless, symptoms of asthenopia, fatigue, astheni a, blurred vision, headache and slight fever, which were noted at one and three years after the satin incident, are thought to be later sequelae of the exposure, for the following reasons: 1) these complaints broke out dose-dependently, as showing the findings that the victims who had symptoms at one and three years after the incident were exposed to relatively high levels of satin because as they were in close proximity to the site where the satin was released; that the more severe satin victims were found immediately after satin exposure, the greater the symptoms remained, because the majority of such persons required hospitalization and/or those who had lower R-AChE activity at the early stage of the intoxication, 2) the prevalence of these symptoms was significantly greater in the victim group than in the non-victim group, 3) some of these complaints might be persisting symptoms due to satin exposure, and 4) the odds ratios of these symptoms in the satinexposed group were clearly high.However, there could be information bias of an overestimated risk of later sequelae in the victim group because of over-recall of each symptom.The risk might be underestimated because of a lower questionnaire compliance in the victim group (35.5% vs 52.5% in non-victim group).However, this may be offset by the higher recovery in the admitted (67.5% vs 11.3% in non-patient group) and outpatient groups (69.9%).
In additional surveys plus clinical investigations, seven of 31 people admitted were diagnosed to have sequelae: four showed epileptic electroencephalographical changes; three had arrtyth-

Figure 1
Figure 1.Geographical distribution of symptomatic victims of sarin exposure in Matsumoto City.Each figure represents the percentage.•oe,Sarin released site.The majority (80%) of victims were present in an area within the darkened area.

Table 2 .
The relationship between cholinesterase activity four weeks after sarin exposure and symptoms one year after the sarin incident.