1985 Volume 52 Issue 6 Pages 700-707
Seroepidemiology of diphtheria in Chiang Mai, North Thailand through 1977 to 1982 and development of the antitoxin in the blood of children immunized with the toxoid were studied. Antitoxin titers of 763 sera with unknown immunization history and of 1, 059 sera with known immunization history were determined by using the microneutralization-cell culture method.
Among persons with unknown immunization history, the percentage of the antitoxinpositive in 10-14 years old subjects in 1979 was higher, as compared with the same age group in 1977, while that in 20 or more years old subjects in 1977 and 1980 were lower than in 1979. Percentage of the antitoxin-positive sera increased according to age. Geometric mean titer of the antitoxin-positive sera in 15-19 year-old subjects was higher in 1979 than in 1977, and higher also than in 5-9 year-old subjects in 1979.
All of the children being immunized in accordance with strict regulations of the Comprehensive Child Care Clinic, Chiang Mai University had the positive antibody. In experiments with this group, a significant increase in the antitoxin titer was observed one month after the booster immunization, and a gradual decrease of the antitoxin titer was observed through 1 to 37-71 months after the last booster immunization in the group of 5-9 years old. Decline of the titer was not observed in the group of 10-17 years old through 16 100 months after the last booster immunization, and the geometric mean titers of this group were 0.580 or more IU/ml.
In Wat Kau Khum school in the suburbs of Chiang Mai, one shot of the immunization produced the seroconversion in 88.2% of the children, and the geometric mean anti-toxin titer of the antibody-positive sera was 4.491 IU/m/ after the one shot.
