A diphtheria outbreak in Johor Bahru, Malaysia: Public health investigation and response

Abstract

Introduction: Diphtheria is an acute infectious disease caused by Corynebacterium diphtheriae. Although the incidence of diphtheria worldwide has rapidly declined following the largely successful diphtheria toxoid-based vaccines, concerns persist for those who were unvaccinated or incompletely vaccinated. In this report, we describe a recent diphtheria outbreak in Malaysia involving four confirmed diphtheria cases. Methodology: The outbreak investigation efforts and epidemiological characteristics of a diphtheria outbreak in Malaysia are described. For all suspected cases, swabs were taken and sent for isolation of Corynebacterium diphtheriae and confirmation of toxigenic strains. Results: The index case was a two-year-old child living with his family in a welfare home. Following contact tracing efforts and investigation for suspected cases, seven samples came back as culture positive for Corynebacterium diphtheriae. Confirmation of toxigenic strains was performed using PCR and Elek’s test, which showed 100% correlation in positivity for four of the samples. All four confirmed cases were below 18 years of age, and three of them did not have complete vaccination history (two unvaccinated, one unknown). The index case eventually succumbed due to severe diphtheria with multiorgan failure while all the other cases were discharged healthy. Conclusions: In Malaysia, despite good vaccination coverage, sporadic diphtheria outbreaks still occur. The rising trend of cases reported over the recent years underscores the need to remain vigilant. Addressing pockets of unvaccinated children and potential waning immunity levels in the population remains pivotal.