Since a number of heat-resistant Clostridium perfringens have often been harbored in the intestine of a normal healthy people: 1) It is necessary to confirm complete agreements in the sero-type of the isolates of incriminated foods and of patient feces, when we make a retrospective laboratory diagnosis on food poisoning cases in which Cl. perfringens have been suspected as a causal agent. 2) If we failed to obtain the incriminated food, it becomes more difficult to determine the causal agent. viz., it is required to prove that more than 90% of the patients is discharging the same sero-type of organism within their 3rd day of the illness, and more than 70% on their 7th day respectively.
During 1963-69, there were 9 cases of outbreak of food poisoning due to heat-resistant Cl. perfringens in Tokyo. These are summerized as follows;
Case 1: On 20-21st of September 1963, a large scale food poisoning occurred, affecting a total of 1, 491 out of 1, 968 employees (affection rate 75.8%) of the 38 companies, who took a lunch delivered by the same caterer. The patients complained of diarrhea and abdominal pain within 8-15 hours after the ingestion of the lunch. Boiled whale meat contained in the lunch was supposed to be the incriminated food, which had been allowed to stand at room temperature overnight after cooking. Hobbs' type 4 organism was isolated from the meat. On the other hand, on the 3rd day of the illness, Hobbs' type 1 and 4 were isolated from 293 of 379 feces of the patients. From the fact, as shown in Table 2, the outbreak was presumed to be combined infection with both of Hobbs' type 1 and 4 organisms.
Case 2: On 17-18th of July 1964, 183 out of 242 persons (75.6%) who had eaten pickled horse-mackerel for their lunch at the employees' canteen, complained of diarrhea and abdominal pain. Ninety-nine of 183 feces (71.0%) of the patients, collected on the 7th day of the illness, were positive Hobbs' type 5 organisms. It was then diagnosed as a food poisoning case due to the heat-resistant Cl. perfringens Hobbs' type 5, although the incriminated food was not available.
Case 3: On 3-4th of September 1964, 165 out of 232 persons (71.1%) who took “Inarisushi” one of the Japanese meal for their lunch at the employees' canteen, complained of diarrhea and abdominal pain. Average incubation period was 12.5 hours, and heat-resistant organism Hobbs' type 13 was isolated from 35 of 39 patients (89.7%) on the 3rd day of the illness. Then, it was suspected to be a food poisoning case due to the heat-resistant Cl. perfringens Hobbs' type 13.
Case 4: On 28-30th of April 1966, a total of 657 out of 892 persons (73.7%) of 49 companies, who took Scotch egg for their lunch, which was delivered by the same caterer, complained of diarrhea (86.1%) and abdominal pain (66.1) within 5-30 hours after the ingestion of the lunch. Twenty-two point two per cent of the patient complained of their dullness, but few nausea and vomiting. Hobbs' type 2 (2.8×106) and 4 organism (2.4×106) were detected from 1 gram of scotch egg. Detection rate of the organisms from the patients were 92.7% on the 1-3rd day of the illness. Among the 1, 765 strains of the isolates, 375 strains (21.2%) were typed into Hobbs' type 2, and 1, 133 strains (64.2%) into Hobbs' type 4 respectively. Accordingly, the outbreak would be due to combined infection with Hobbs' type 2 and 4 organisms.
Case 5: On 29th of April 1967, a food poisoning occurred at a certain inn in Kanagawa prefecture, affecting 152 out of 244 persons (62.3%) who had happen to stay at that inn, manifested a typical symptoms of the food poisoning, although failed to point out the incriminated food. Hobbs' type 1 organism was isolated from the feces of all 8 patients on the 4th day of the illness and presumably the cause of the outbreak.
