At 1 year, 54 of 318 victims (17 percent) still reported being symptomatic. More than 80 percent of victims lived closest to the site of sarin release. There were no age or gender differences between those whose acute symptoms either persisted or resolved. The most common symptoms were asthenopia11 (38/54), fatigue (35/54), blurred vision (30/54), shoulder stiffness (19/54), and asthenia12 (18/54). At 3 years, 27.5 percent of 167 victims reported being symptomatic, compared with 5.4 percent of controls. The odds ratios were highest for fatigue, headache, and visual disturbances (asthenopia, blurred vision, and narrowing of visual field) (Table 5.5). The limitations of the study were low response rate at 3 years (41.8 percent) and possible recall bias (Nakajima et al., 1999). It must also be pointed out that the controls were not necessarily unexposed; they likely were a mixed population of unexposed and low-level exposed individuals.
The Matsumoto experience shows that direct exposure to sarin, particularly at intermediate to high levels, is associated with the acute cholinergic syndrome. In the majority of sarin victims in Matsumoto, clinical signs and symptoms of acute sarin poisoning disappeared within a matter of days or weeks if victims survived the acute effects of respiratory failure and convulsions. Follow-up population-based studies of sarin victims in Matsumoto show that significant chronic symptoms from sarin exposure persist and include visual disturbance (asthenopia, blurred vision), fatigue or asthenia, and headache. These chronic symptoms appear to be dose dependent, given the geographic exposure data and documented clinical and laboratory findings. These follow-up studies, however, lack a well-defined control population.
On the morning of March 20, 1995, terrorists simultaneously released diluted sarin vapor into three convergent lines of the Tokyo subway system (Yokoyama et al., 1998c). About 5,000 people sought medical evaluation, 1,000 of whom were symptomatic and 12 of whom died (Woodall, 1997). The hospital in closest proximity to the attacks, St. Luke’s International Hospital, treated the largest group of patients (n = 641) (Okumura et al., 1996; Ohbu et al., 1997). Medical staff assessed most of these patients (83 percent) as having an intermediate level of exposure based on miosis (the most common symptom), blurred vision, and headache. Seventeen percent of the patients were presumed to have had high-level exposure. This patient group, which was admitted to the hospital, had more severe cholinergic signs and symptoms including marked miosis, weakness, difficulty breathing, fasciculations, convulsions, and >20 percent depression of cholinesterase activity in the blood. Most of these patients were given standard treatment for acute sarin intoxication (atropine, pralidoxime chloride, and diazepam). Five patients were critically ill with cardiac arrest, res-