Seroepidemiological survey of diphtheria in Thailand and the effect of a triple vaccine (DTP)

Abstract

Sera from 2, 013 persons aged 0-75 years including cord bloods were collected at different areas in Thailand by the Society for Medical Research in South-East Asia, Nippon Medical School in 1977-1981. These sera were examined by the micro cell culture method for determi-nation of diphtheria antitoxin titer using Vero cells.1) Except Chiang Mai '80-'81, diphtheria antitoxin (> 0.02IU/ml) were found in 81.2% of cord bloods, 67.1, 05 of children at the age of 1-12 months old, 37.9% of 1-2 years old, 55.3 % of 3-4 years old, 58.8% of 5-9 years old, 71.5-78.1, 06 of 10-19 years old, and 90.1% of older than 20 years.2) Geometrical mean titers of the antitoxin-positive sera were 0.153IU/ml in cord bloods, 0.140-0.141IU/ml at 0-9 years old, 0.193IU/ml at 10-14 years old, 0.180IU/ml at 15-19 years old, and 0.151 IU/ml at older than 20 years.3) In 68 paired serum samples from mothers and newborns (cord bloods), the antitoxin titer corresponded well each other. Antitoxin level of newborns were retained up to the age of 6 months.4) Considering the age related antitoxin status of different areas, it was recognized that diphtheria had become common in northern part of Thailand since 1978, and reached the outbreak in Chiang Mai, 1980.5) Antitoxin status by age were somewhat different in different geografical areas. People in Raming Tea Plantation and a Musur village in Chiang Mai Province had low diphtheria antitoxin level.6) Antitoxin positive rate and geometrical mean titer of antitoxin-positive sera in Chiang Mai '80-'81 were apparently higher than either of other areas or Chiang Mai '77-'79. This high antitoxin level could be explained by the diphtheria-toxoid immunization and the diphtheria outbreak in Chiang Mai, 1980.7) Surveys of diphtheria antitoxin in 143 serum samples from children aged 0-14 years showed that the immunization schedule by the Comprehensive Child Care Clinic, Chiang Mai University was efficient to confer the diphtheria immunity. Two shots of the primary immunization increased the antitoxin-positive rate from 16.7% (2/12) to 71.496 (5/7) of newborns. The primary plus the first booster immunization evoked higher than 0.02IU/ml of the antitoxin in 100% of the children. The geometrical mean titer of antitoxin was 6.912IU/ml after one month, and 0.540-1.144IU/ml after 11-64 months of the last booster immunization. Geometrical mean titer of antitoxin after 11 months or more of the first booster (0.438IU/ml) was lower than those after 11 months or more of the second (0.912IU/ml) and the third (2.318IU/ml) booster immunization.8) One hundred and two school-children aged 8-14 years without any record of the imm-unization with diphtheria toxoid in the suburbs of Chiang Mai received one shot of the toxoid during the epidemic of diphtheria in 1980. After one month, 88.2% of the children had the antitoxin in their sera and the geometrical mean titer of the antitoxin was 4.491IU/ml, which decreased to 1.057IU/ml after one year.