Abstract
In order to investigate the inapparent infection of poliovirus, isolation of the virus from feces and neutralization tests (NT) were carried out on fifty healthy infants and children who were randomly selected from general population in Arakawa and Shinagawa area, Tokyo, and forty one healthy infants and children of two nurseries in Tokyo from May to Oct. of 1957. The feces for the virus isolation were collected from those infants and children once a month during that period. The NT antibodies was examined on two serum samples taken in May and October, during which poliovirus infection might be prevalent. The results were as follows:
1) Poliovirus and the other enteroviruses were isolated from 12% of 183 fecal specimens collected in Arakawa and Shinagawa areas, and 38% of them were poliovirus and 8.1% the enteroviruses. 5.9%, of 17 sera collected from the children in Arakawa area and 33.3%, of 9 sera collected from the children in Shinagawa area showed positive conversion of the NT antibody against poliovirus between May and October.
2) These investigations indicatedd that 21.1%, of 38 infants and children from general population of Tokyo who were successivelly observed during six months, suffering from the inapparent infection with poliovirus, namely, the inapparent infection rate of poliovirus was 21.1% of healthy infants and children under 2 years of age in Arakawa and Shinagawa areas during 6 months of the summer of 1957. Since the population under 2 years of age in Arakawa and Shinagawa areas was 27, 128, and four had developed paralytic poliomyelitis during the same period, it was calculated that a patient with paralysis was probably surrounded by 1431 individuals of the inapparent infection.
3) The age distributions of the inapparent infection rate were 21.4% from 6m to 11m old, 25% from 1y to 2y old, but that of children elder them 2 years old was not clear.
4) In K and H nurseries the inapparent infections were found in 93.3 and 100 percent of 15 and 17 infants respectively. It reveales quite high infection, rate of poliovirus in such groups as nursery or household, if the virus is once introduced.
5) The high incidence of infection with ECHO type 6 and ECHO type 7 were observed in K and H nursery respectively about the same time to the poliovirus episode. The age distribution of NT antibodies against ECHO type 7 virus isolated from H nursery were tested in 71 sera collected in Tokyo; the results indicated that the rate of antibody positives was lower than that of polio NT antibodies even in higher age groups.
