Isolation of influenza virus C from influenza cases in 1999/2000 season - Saitama
(IASR 2000; 21: 146-147)

In Saitama Prefecture, A/H1 and A/H3 are primary influenza subtypes for the 1999/2000 season. In total 293 influenza viruses A, including 185 A /H1 and 108 A/H3, are isolated in Saitama Prefecture. During this season, influenza C is isolated from 2 geographically apart specimens.

Case 1: On January 24, 2000, one year old boy developed 38.5C fever, cough, runny nose, and fatigue. Gargling fluid was collected on the same day. He presented fever for 2 days and he was recovered. He had no history of getting out of his hometown. Although influenza epidemic reached a peak in the town, neither of his parents and grand parents presented any symptoms. He was given influenza vaccine twice in the end of November and early December.

Case 2: On February 28, 2000, 4 years old girl developed 40C fever, cough, runny nose. Gargling fluid was collected on the following day. She presented those symptoms for 5-6 days, and she was recovered. Her brother and some of her friends in kindergarten presented similar symptoms, but specimen was not collected. She was not vaccinated. Two specimens were inoculated on several tissue culture, and a week later weak cytopathic effect (CPE) was observed on MDCK cell. Chicken red blood cell (RBC) was agglutinated (1:4~8), but agglutination was not observed with guinea pig RBC. The isolates were continuously cultured by MDCK cell, and on the third day agglutination titer increased 1:32~64. Results of CPE and RBC agglutination (chicken RBC positive, guinea pig RBC negative) suggested influenza C pattern. Influenza A was ruled out by negative result of Directigen A test. Clear NS gene, which is known in influenza C, was amplified by reverse transcriptase polymerase chain reaction (RT-PCR). The isolates were identified as C/Ann Arbor/1/50 by hemagglutination inhibition test carried out at the Virus Research Center, the Sendai National Hospital.

Number of influenza C isolate is extremely few, comparing those of influenza A and B. In Japan influenza C is isolated sporadically throughout of a year. However, it is reported that the virus implicates outbreak at nursery and 3 months long local epidemic.

Reported by Shinichi Shimada, Michiyo Shinohara, Kazue Uchida, Yukari Segawa, and Yoji Hoshino, Dept. of Infectious Diseases, Saitama Institute of Public Health;Kuniaki Suzuki, Suzuki Children's Clinic;Katsumi Arai, Dept. of Pediatrics, Chichibu City Hospital.

Correspondence; Shinichi Shimada;
Fax: +81-48-840-1041

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