Factors associated with outbreak of diphtheria in Kafanchan, Kaduna State, Nigeria: July-October 2023

The year 2023 witnessed the re-emergence of diphtheria in Nigeria. Kafanchan, Kaduna State, reported an unusual surge in cases and deaths. We investigated the outbreak to identify associated risk factors of the disease. We conducted an unmatched (1:2) case-control study. Case-patients were identified through the State linelist and traced to their residence. At the same time, controls were randomly selected from neighbors without symptoms or signs suggestive of diphtheria within the same community. Data was collected using an interviewer-administered structured questionnaire. Bivariate analysis was done to ascertain the odds ratio (OR), while multivariate logistic regression analysis was done to calculate the adjusted odds ratio (aOR). The confidence interval (CI) was set at 95%. A total of 91 case-patients and 182 controls were recruited. The median age of case-patients was 7 years (5-10 years). Forty (44%) of 91 case-patients were females. Sixty-four (70%) of 91 case-patients were from Kafanchan ward B, and the case fatality rate was 23%. Exposure to pentavalent vaccination was found to be associated with protection from diphtheria (aOR: 0.39, 95% CI: 0.20-0.77). Thirty-one (34.07%) of 91 case-patients had contact with someone with respiratory symptoms [OR = 37.2; 95% CI = 16.8-82.6; p <0.001]. Thirty-seven (40.66%) of 91 case-patients had contact with a confirmed case [OR = 25.1; 95% CI = 11.7-53.8; p < 0.001]. Twenty-three (25%) of 91 case-patients had never received the pentavalent vaccine, and the primary reason cited by caregivers was that they were unaware of any benefits of vaccination. The outbreak is attributable to suboptimal pentavalent vaccination coverage. Future outbreaks may be avoided or their impact reduced through improved risk communication and community engagement on the benefits of vaccination, strengthening routine immunization services, early warning surveillance, and prepositioning of diphtheria antitoxin (DAT) and antibiotics.