An outbreak of SRSV food poisoning suspected from antibody rise of patients in ELISA with empty particles of SRSV as antigen - Miyazaki
(IASR 1999; 20: 267-268)

On January 7, 1999, an outbreak of food-poisoning occurred among those who stayed at a "ryokan" hostel in Miyazaki Prefecture. Investigation by the local health center revealed that implicated meal was lunch box, which was prepared by kitchen A on January 5, however, food item was not confirmed. Number of exposed reached 412, most of them were high school and college students, and 241 developed illness. Average incubation period was 34.1 hours and major symptoms are vomiting (74%, average 4.5 times), diarrhea (68%, average 3 times), abdominal pain (61%), fever (59%, maximum 38C), and headache (54%).

Because of season occurred and symptoms of the patients, viral food-poisoning was suspected initially. Moreover, an employee of kitchen A presented similar symptoms since the mid-night of January 4, and the investigator confirmed that he joined cooking. In order to detect virus particle by electron microscope (EM) and to measure antibody titer by ELISA, 10 stool specimens and 22 acute phase sera from the patients, as well as 5 sera and 3 stool samples from the employees were collected. Convarescent sera were collected 2 weeks later.

Norwalk-like virus was detected by EM from 7 of 10 patients' stool samples, and SRSV was attributed to the food-poisoning. Whereas, virus particle was not observed from the employees' samples.

Paired-serum samples were collected from 5 patients and 5 employees for ELISA. ELISA kit was provided by Katsuro Natori, the Virology 2, NIID. Two kinds of anti-SRSV Virus-like particle (VLP) [rCV16 (genogroup I) and r97K47 (genogroup II)] were used as antigen. Antibody titer was measured by instructions of attached annual. Sera were diluted 1:200, 1:800, and 1:3,200 and dropped onto the fixed antigens. Horseradish peroxidase-labeled anti-human immunogloblin goat IgG was used for the secondary antibody, and o-phenylenediamine (OPD) dihydrochloride was used for substance. Results of 4 patients and 3 employees are displayed in Figure. Antibody titer against both antigens, especially r97K47, was increased.

When food-poisoning due to SRSV is suspected, we request the investigators to collect serum, as well as stool, from patients and food handlers. Collected paired-serum was examined by immunoelectron microscopy, however, we have often experienced that unhomologous virus particle prevents successful results. It is easy to measure antibody titer by ELISA, and results are more objective than EM. We concluded ELISA is a useful method.

Reported by Seigo Yamamoto, Kazuhiro Kizoe, and Syuji Yoshino, Miyazaki Prefecutural Institute for Public Health and Environment.

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