Epidemiological and Serological Study of Re-emerging Diphtheria in Dansai District, Loei Province, Thailand, June to October 2012

Abstract

In July 2012, two fatal cases of diphtheria were reported from Dansai District of Loei Province, where had been free from diphtheria for a decade. An investigation was conducted to confirm the etiology, identify source of the outbreak and measure the prevalence of antibody to diphtheria toxin among the population. Medical records were reviewed. Active case finding and throat swab screening were done in all villages. Throat swab samples were sent for culture. Corynebacterium diphtheriae isolates were sent for toxin testing and a subset for multi-locus sequence typing (MLST). A serological survey of diphtheria antibody was done in 132 respondents in two villages. A total of 37 cases and 26 carriers were found. Total 18 (48.6%) cases were children. Two fatal cases (5.4%) were adults. All 16 (61.5%) children carriers had received the recommended doses of DTP or dT from the EPI program in the past. In the serological survey, 39.4% (52/132) had protective antibody, including 68.8% (11/16) of children and 35.3% (41/116) of adults. About 79% of people who had protective level received at least one dose of diphtheria toxoid. With MLST, three new subtypes were identified, including ST243, ST244 and ST245. Dansai outbreak was confirmed with the emergence of new pathogenic strains. A low proportion of sera (39.4%) had protective antibody level. A booster dose of diphtheria and tetanus toxoid should be considered.