[Influenza virus surveillance in Tama, Tokyo--viral examinations in 1996/97, 1997/98, 1998/99, and 1999/2000 seasons].
During the 1996/97, 1997/98, 1998/99, and 1999/2000 seasons, isolations of influenza virus and/or confirmations of hemagglutinin gene of virus from the throat swab of patients in 9 medical institutions in Tama, Tokyo were carried out by RT-PCR and tissue culture with MDCK cells. In 1996/97 and 1997/98 seasons, type A (H3N2) was the predominant type of influenza virus, which was 85% in the 1996/97 and 97% in the 1997/98, but small-scale outbreaks with type B virus was also confirmed in the 1996/97 season (during the 8th and 10th week). On the other hand, in the other two seasons, 2 different kinds of types of virus were discovered, which was type A (H3N2) and type B in 1998/99 season, and H3N2 and H1N1 of type A virus in 1999/2000 season. In the 1998/99 season, type A (H3N2) prevailed in the first half, and type B gradually replaced type A (H3N2) after the 5th week in 1999, whereas 2 different kinds of type A in the 1999/2000 mixed during the outbreak. From the presented data, the difference of mode by age groups and year could be explained. Namely, most specimens and positive cases in 1996/97 and 1997/98 seasons were those from low age groups (fifteen years of age and below). In 1998/99 and 1999/2000 seasons, the number of specimens from high age groups (sixteen years of age or over) accounted for above 50%, and about 70% of type A (H3N2)-positive cases. Contrary, the frequency of type B virus in 1998/99 season and type A (H1N1) in 1999/2000 season was higher in the low age groups than the high ones.
Ogata
K
K
Tama Branch Laboratory, Tokyo Metropolitan Research Laboratory of Public Health.
Kato
R
R
Hayashi
Y
Y
Ito
T
T
Yamada
S
S
D006387:Hemagglutination, Viral / Q000235:genetics; D006801:Humans; D009980:Influenza A virus / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D007564:Japan / Q000453:epidemiology; D011159:Population Surveillance; D012621:Seasons