Jpn.J.Infect.Dis., 52,1999
Laboratory and Epidemiology Communications
An Outbreak of Pharyngitis Caused by Food-Borne Group A Streptococcus
Masakodo Matsumoto, Yoshio Miwa, Hironori Matsui, Makoto Saito, Michio Ohta1 and Yutaka Miyazaki*
Aichi Prefectural Institute of Public Health, 7-6 Nagare, Tsuji-Machi, Kita-Ku, Nagoya 462-8576 and 1Department of Bacteriology, Nagoya University School of Medicine, 65 Tsurumai-Cho, Showa-Ku, Nagoya 466-8575, Aichi, Japan
Communicated by Yutaka Miyazaki
(Accepted June 16, 1999)
The present report discusses an outbreak of food poisoning caused by Group A Streptococci. A company in Aichi Prefecture with 303 employees held a sports meeting in May 1996. A total of 255 employees participated in the meeting. At noon, the participants were served lunch, which had been preparared by a restaurant and brought to the meeting place three hours earlier. Most participants took lunch at the meeting place but others brought the food home. In total, 244 individuals fell ill: 192 were employees who participated in the sports meeting and 52 were their family members. Among the patients, 236 actually ingested the food, but eight other patients did not. Here, an additional sencondary spread was suspected.
The symptoms are summarized in Table 1. Eighty percent of the patients had symptoms of pharyngitis and ten percent those of food poisoning, such as diarrhea, nausea, and vomiting. The date of the disease onset could be determined in 189 patients; 6 (8.5%) developed a symptom in the afternoon of the same day, 100 (52.9%) on the following day, 66 (34.9%) two days later, 6 (8.5%) three days later, and one (0.05%) four days later. The disease onset thus followed a curve with the single peak at day one, which suggested a single causal event in this outbreak.
From pharyngeal washes from four patients among five who were examined, group A Streptococci of T1 serotype were isolated by culturing in the N-O medium (1). Comparison of serum ASO (Anti-Streptolysin O) and ASK (Anti-Streptokinase) levels on day 6 and day 16 revealed a significant rise in four patients (Table 2).
The remains of the lunches were examined for bacteria four days after the event. They were not well-preserved, however. Though Salmonellae and Vibrios were not detected, 105 -107 CFU /g group AStreptococci were isolated from the boiled eggs, fried boiled fish-pastes, fried chickens, and boiled seaweed rice (Wakame-Gohan) (Table 3); Staphylococci , Escherichia coli and other bacteria were present also in large qunatities. However, the bacterial counts indicated here may not reflect the amount of bacteria ingested by the patients, as the food was not well-preserved.
Pulsed-field gel electrophoresis (PFGE) of the SmaI-digested chromosomal DNA (2) revealed the identical pattern for all of the Streptococci isolates.
The evidence from the laboratory as well as epidemiological evidence strongly suggested the outbreak was caused by ingestion of cooked foods which were contaminated by Group A Streptococci (serotype T1). However, it was not determined how the food had been contaminated by the bacteria. Pharyngeal washes from ten employees of the restaurant, including four employees who prepared the suspected lunches, were examined for the Group A Streptococci one month after the event. All employees tested negative for the bacteria. Though Group A Streptococci- indued food poisoning is rare, several such outbreaks have been reported in Japan, such as those in Fukuoka and Ibaragi Prefectures (3,4). More research will be needed for clarifying the route of infection and persistence of the bacteria in cooked foods.
We thank the staff of the regional health office for the epidemiological information and Dr. H. Igarashi, Kokusaigakuin Saitama Junior College, for his advice.
REFERENCES
*Corresponding author : FAX:+81-52-913-3641, E-mail:joho-ph@pref.aichi.jp
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