An influenza Epidemic among Institutionalized Children at the Time of Replacement from A(H3N2)to A(H1N1): Observation of 32 Cases Including 3 Cases of Probable Simultaneous Infection with A(H1N1) and A(H3N2)

An influenza epidemic occurred in Fukuoka, southern part of Japan in January, 1978 in which both influenza virus A(H1N1) and A (H3N2) were isolated. Thirty-two institutionalized children with influenza were studied at the time of this shift from A (H3N2) to A (H1N1). Fourteen virus strains were isolated. Thirteen strains belonged to influenza virus A (H1N1) (A/USSR/92/77-like strain) and one a mixed strain of A (H1N1) and A (H3N2) (A/Texas/77-like strain). The hemagglutination inhibition (H1)tests of paired sera indicated that of the 32 Children, 27 Showed a significant increasein HI antibody titers for influenza virus A (H1N1). 2 for A (H3N2) and the remaining 3, including the case from which the mixed virus strain was isolated, for both A (H1N1) and A (H3N2). These offers 3 cases were thought to be probably infected simulataneously with both influenza virus A (H1N1) and A (H3N2). Clinical manifestations due to influenza virus A (H1N1) were moderate and the 3 cases of probable simultaneous infection with both influenza virus A (H1N1) and A (H3N2) did not show two clinical episodes but rather a single episode with clinical manifestations similar to the cases with single virus infection.